Review Article

Arch. Dis. Childh., 1967, 42, 341.

Sugar MalabsorptionDue to Deficiencies of Disaccharidase Activities and of

Monosaccharide TransportA. HOLZEL

From the Department of Child Health, University of Manchester

In many societies including our own, carbo-hydrates play a major part in the total calorie supply.According to the National Food survey figures(Greaves and Hollingsworth, 1964), the averagedaily diet of adults contains nearly 350 g. of thisconstituent. Diets of course vary with eatinghabits and social class, but the dietary carbohydratesare largely ingested as poly-, oligo-, and disaccha-rides. In the very young, however, the carbo-hydrate intake may consist almost entirely ofdisaccharides, though this phase is now gettingprogressively shorter. As the rapid decrease inbreast-feeding has been followed by the earlyintroduction of cereals into the cow's milk formulae,even the infant of only a few weeks of age has alsoto digest polysaccharides.The percentage of calories derived from carbo-

hydrate increases from 40% in infancy to well over50% later in life. The polysaccharides, starch andglycogen, are hydrolysed by salivary and pancreaticamylase to maltose and small quantities of isomal-tose and glucose. The common disaccharides inour food are lactose and sucrose. The amount oflactose depends on the milk intake, as this is its mainsource. The human intestinal mucosa has there-fore the task of absorbing large quantities of thedisaccharides, maltose, isomaltose, sucrose, andlactose. For a long time surprisingly little attentionwas paid to this important absorptive function of thesmall intestine, but during recent years physiologists,biochemists, and paediatricians have discoveredmuch of interest, and clinical observations haverevealed a number of disorders associated withsugar malabsorption.

Physiology of Disaccharide AbsorptionUntil a few years ago it had been accepted that

hydrolysis of the disaccharides into their componentmonosaccharides had to precede their absorptionand entry into the further stages of metabolism, andthat the disaccharidases, lactase, sucrase, and

maltase, were secreted by unspecified cells of theintestinal mucosa into the lumen of the gut wherethe hydrolytic process took place. But studies inman during the past decade (Borgstrom, Dahlqvist,Lundh, and Sjovall, 1957; Dahlqvist and Borgstrom,1961) demonstrated that disaccharidase activity inthe intestinal lumen was extremely limited and didnot account for the amount of carbohydrateabsorbed. They further indicated that the majorityof disaccharides were absorbed unhydrolysed andsplit intracellularly, a fact that accorded well withexperimental findings (Cajori, 1933; Fridhandlerand Quastel, 1955).The problem of localization of the sugar-splitting

enzymes was brought nearer its solution by Millerand Crane (1961), who were able to separate thebrush-border from the rest of the intestinal mucosaof the hamster, and found that the whole of theenzyme activity of the mucosa was accounted for bythis layer. (-galactosidase (lactase) activity hadbeen localized in the microsomes of the rat intestinalmucosa by Doell and Kretchmer (1962), whileDahlqvist and Brun (1962), employing histochemi-cal methods for the recognition of invertase andtrehalase in various animal tissues, associated theiractivity with cytoplasmic granules. As yet there isno definite information concerning the possiblerelationship of the elements of fine structure of themicrovillus with its absorptive and digestivefunctions. However, two related fractions havebeen obtained by density gradient centrifugation oftris-disrupted brush-borders from hamster intesti-nal mucosa, and have been identified as the micro-villus cores and their surrounding membranouscoats (Overton, Eichholz, and Crane, 1965;Eichholz and Crane, 1965).

Specificity of human intestinal disacchari-dases. The belief that each enzyme has itscorresponding specific substrate has been modifiedin so far as experimental and practical experience

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has shown that synthetic sugars which have thesame glycosidic linkage as naturally occurringproducts will be split by the same enzyme.The following human intestinal disaccharidases

have been identified by heat inactivation experi-ments (Dahlqvist, 1962; Dahlqvist, Auricchio,Semenza, and Prader, 1963), gel-filtration onSephadex and chromatography (Auricchio, Semenza,and Rubino, 1965c; Semenza, Auricchio, andRubino, 1965a). The maltases or ao-glycosidaseshydrolyse maltose, isomaltose, sucrose, and palati-nose. Trehalase exerts its activity on trehalose, arare disaccharide that occurs in certain mushrooms.The 3-glycosidase lactase (P-galactosidase) attackscellobiose, in addition to lactose. Cellobiose is adisaccharide resulting from the digestion ofcellulose, which consists of two molecules ofglucose with a 1-4 3 linkage similar to that whichjoins the glucose and galactose molecules inlactose (Fig. 1). Although cellobiose plays little

, galoctosi dase

* *I * a~~* 0 *4 * **

0 00

Lactose Cellobiose

FIG. 1.-f-galactosidase hydrolyses two disaccharidesof different molecular composition but with the same

glycosidic linkage.

part in human nutrition, since cellulose cannot behydrolysed in the small intestine, the sugar can beused as an additional substrate to verify lactaseactivity. The presence of two intestinal lactaseswas demonstrated by Heilskov (1956) for the calf,and for the rat and rabbit by Doell and Kretchmer(1962), who found one lactase associated with theparticulate fraction which hydrolyses two substrates,namely lactose and ortho-nitrophenyl-3-galactoside,while the soluble enzyme splits only the latter.Since ortho-nitrophenyl-3-galactoside is an artificialcompound, the true function of the second enzymeis unknown. Two lactases have also been postula-ted for the human intestinal mucosa (Semenza et al.,1965a). These authors have been able to show thatthe two 3-galactosidases in the mucosa of thehuman jejunum and ileum are not the result of anartefact, and that the ratio of cellobiase activityremains constant in relation to that of each of thelactases, further indicating that cellobiase andlactase activity are due to the same enzyme molecule.With regard to the multiplicity of human maltases,Dahlqvist (1964a) and Auricchio et al. (1965c) come

to slightly different conclusions, and thus to some-what differing nomenclature. Dahlqvist recognizesfour maltases, while Auricchio and colleaguesseparate five (Table I).

TABLE IClassification of Maltases

Dahlqvist (1964a) Auricchio et al. (1965c)

Enzyme Substrate EnzymeMaltase Ia Isomaltose Maltase 5(isomaltase palatinase) Palatinose (isomaltase palatinase)

MaltoseMaltase Ib Sucrose Maltase 3 (sucrase)

(sucrase: invertase) Maltose Maltase 4Maltase II Maltose Maltase 2Maltase III Maltose Maltase I

Maltase 5 (in the latter classification) hydrolysesmaltose, isomaltose, and palatinose, a synthetic sugarconsisting of one molecule glucose and one moleculefructose in 1-6o0 linkage. Since palatinose andisomaltose have the same glycosidic bond, they aresplit by the same disaccharidase (Fig. 2). Palatinosecan therefore be used to demonstrate isomaltaseactivity (Auricchio, Prader, Murset, and Witt, 1961)when isomaltose is in short supply (Fig. 2).

MALTASESInvertase Isomaltose

* ff<2* 0 0 S

* 0 0 :** * 4

* 0 0 * 0 0 0 0* 0 0 6 0 6 0 0Sucrose somaltose Polotinose Maltose

FIG. 2.-Isomaltase hydrolyses in addition to isomaltosepalatinose, a synthetic disaccharide.

Distribution of disaccharidases along thesmall intestine. Comparison of a number ofpublished animal and human investigations revealsthe presence of species differences. In the rat,lactose activity is stronger in the middle part of thesmall intestine than in its proximal or distal regions,maltase activity is uniformly distributed, whilesucrase (invertase) and isomaltase are strongest inthe proximal areas. In the adult pig, the trehalase,lactase, and cellobiase activities are strongest in theproximal part, while the maltases are most active inthe distal part (Dahlqvist, 1964a). In adult man,according to Auricchio, Rubino, and Miirset (1965a),enzyme assays on mucosal specimens obtained byperoral intestinal biopsy indicate that sucrase,isomaltase, and lactase are less active in the first partthan in the remainder of the duodenum; in theupper jejunum and the last segments of the ileum

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Sugar Malabsorptiondisaccharidase activities are of the same order ofmagnitude. Taking the rate of absorption as ameasure of disaccharidase activity, Gray andIngelfinger (1965) found, with the aid of infusionexperiments, that sucrose absorption was abouttwice as rapid in the human jejunum as in the ileum.Ingested sucrose was almost completely absorbed inthe jejunum. In a study of 7 normal adults, 6 menand 1 woman, Newcomer and McGill (1966)carried out 6 to 13 peroral mucosal biopsies in eachsubject at various levels of the small intestine fromthe first part of the duodenum until well into theileum. Lactase, sucrase, and maltase activities weredetermined; disaccharidase activity was low in theduodenum and ileum, while peak activity was foundat variable points in the jejunum and proximal ileum.

Foetal and neonatal intestinal disacchari-dase activity. The prenatal and postnatal develop-ment of disaccharidase activities is of importancenot only for academic reasons, but also in connexionwith the practical management of the very smallpremature infants. Lactosuria in the prematurebaby was recognized and explained half a centuryago by the absence of lactase activity (Langstein andMeyer, 1914), the enzyme being functional in thefull-term infant. An investigation of 32 humanembryos, foetuses, and newborn infants (Auricchioet al., 1965a) revealed that the enzyme activities weredistributed uniformly throughout the small intestineexcept in the duodenum and terminal ileum, whereonly trehalase remained high. All glycosidaseswere present by the third month of intrauterine life.All a-disaccharidases (namely the maltases andsucrase) reached a maximum during the sixth orseventh month of intrauterine life while the 3-glycosidases, lactase and cellobiase, developed moreslowly before birth and reached their peak at term.Premature infants had a low level of lactase activitywhich, however, rose rapidly in the postnatal periodindependent of milk intake. Dahlqvist and Lind-berg (1966), who studied human foetuses between11 and 23 weeks of intrauterine life, found invertaseand isomaltase activities fully developed before the11th week, trehalase between the 11th and 23rdweek, while the maltases that act only on a maltosesubstrate could not be detected.

Foetal meconium had a high enzyme activity,probably originating from desquamated mucosalcells, but the meconium obtained shortly after birthfrom term infants was devoid of disaccharidases.Alkaline phosphatase, which seems to be morestable, was extremely active.

In some mammals such as rats, pigs, and cows,lactase activity is highest in the newborn and

decreases gradually to its lowest level in the adultspecimen. In other animals such as mice, rabbits,and guinea-pigs, the P-galactosidase activity maydecrease at different rates in the jejunum and ileum(Koldovsky, Heringova, Jirsova, Chytil, andHoskova, 1966) according to the pH. In rats andpigs, sucrase (invertase) activity is not evident atbirth, but develops later. Injections of hydrocorti-sone into young rats caused invertase activity in thesmall intestine to appear at an earlier stage thannormal (Doell and Kretchmer, 1964). This wasfurther supported by immunochemical studies witha fluorescent antibody technique (Doell, Rosen, andKretchmer, 1965). In man, lactase activity remainsat a high level provided it is not altered by externalfactors.

Sugar TransportAssuming the disaccharide-splitting enzymes to

be intracellular, the means by which sugars enterthe mucosal cells is still obscure. This could be bydiffusion, if for instance rapid hydrolysis of thedisaccharide within the cell maintained a gradientbetween it and the intraluminal medium. Forglucose and galactose there also exists an activecarrier system. Actively transported sugars, i.e.those transported against a concentration gradient,possess certain structural features in common, apyranose ring, an oxygen bridge between Cl andC5, and a free -OH group at C2.A further essential requisite is the presence of

sodium ions on the membrane of the mucosal cell.Substitution of lithium, magnesium, or choline forsodium prevents active transport. The drivingforce is regarded as a form of biological pump, withadenosine triphosphate (ATP) providing the im-mediate energy source. Ouabain, phlorizin, and2: 4-dinitrophenol inhibit the absorption of glucoseand galactose. It has been suggested that ouabainacts by virtue of its property of disturbing tissueelectrolyte metabolism (Davenport, 1966).

Littman and Hammond (1965) have proposedthat sugars enter the intestinal cell by means of aternary sugar-Na-carrier complex. This carrierwould possess two specific binding sites, one for thesubstrate and one for Na+. The rate of sugartransport seems to be dependent on the differencebetween intracellular and extracellular Na concen-trations, and the driving force is derived from theNa concentration gradient, which is maintained byan ouabain-sensitive mechanism. Czaky's hypo-thesis, however, suggests that it is the energy yieldingsystem which requires intracellular Na for itsactivation and which is inhibited by the cardiacglycosides. The pump part is then an ATP-

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adenosine triphosphatase-sodium complex with aspecific carrier for sugar. According to Semenza,Tosi, Vallotton-Delachaux, and Mulhaupt (1964),human intestinal sucrase is also activated by Na,and a mechanism similar to that of glucose absorp-tion might be responsible for the transport ofsucrose.

Actively transported sugars move far faster than asugar such as fructose which crosses the cellmembrane by diffusion.

Disturbances of the transport mechanism haverecently been implicated in the pathogenesis ofserious metabolic disorders in infancy.

Deficient Lactase ActivityAmong the disaccharidase deficiencies, diminished

or absent, lactase activity is the most important.The congenital and probably hereditary type is rarein childhood, but the acquired type has been foundassociated with a large number of unrelated gastro-intestinal disorders. Lactase seems to be by far themost sensitive of sugar-splitting enzymes in thebrush-border of the small intestinal mucosa.Maybe because of its spatial localization it is bothmore easily damaged than the other disaccharidases,and takes longer to recover function if the injury isreversible.

Congenital alactasia (hypolactasia). Thefirst observation of primary, congenital, and mostlikely hereditary, deficient lactose absorption in twosibs was made by Holzel, Schwarz, and Sutcliffe(1959), who introduced the lactose tolerance test ascircumstantial evidence for lactase activity; follow-ing a lactose loading dose the rise of the bloodglucose level was small compared with that after aglucose-galactose load. 18 cases have subsequentlybeen recorded, of which 15 have been boys and 3girls (Weijers, van de Kamer, Dicke, and Ijsseling,1961; Holzel, 1962, 1965; Thornton, Burkinshaw,and Kawerau, 1962; Davidson, Sobel, Kugler, andPrader, 1964; Durand and La medica, 1962;Lifshitz, 1966; Launiala, Kuitunen, and Visakorpi,1966).Familial incidence and genetic factors. Three

pairs of sibs were found with the condition, butthere have been no cases with consanguineousparents.

Clinical picture. Diarrhoea, as in all the disac-charidase malabsorptions, is the main feature, andstarts within a few days after birth as soon as milkfeeding is well established. Since the lactose con-tent of the food is the factor determining the severityof the alimentary tract manifestations, these are

likely to be more severe in the infant at the breast oron cow's milk formulae enriched with lactose.Deficient hydrolysis of the sugar leads to itsretention in the gut and to an influx of largequantities of water to balance the increase inosmotic pressure.

Bacterial fermentation of the unabsorbed lactoseproduces appreciable quantities of short-chain fattyacids, which account for the low pH of the soursmelling, frothy, loose, or watery stools. Intestinalcolics and extensive excoriation of the buttocks addto the clinical features to form a fairly characteristicpicture.

Since the patients with primary lactase deficiency(hypolactasia or alactasia) are young infants, in onlya few cases has the diagnosis been supported byestimation of 3-galactosidase activity in peroralbiopsy specimens of intestinal mucosa (Davidsonet al., 1964; Lifshitz, 1966; Launiala et al., 1966).

Lactase deficiency in the adult. A syndromenot unlike that seen in young infants with deficientlactase activity was first described in adults byHaemmerli, Kistler, Ammann, Auricchio, andPrader (1963), Haemmerli, Kistler, Ammann,Marthaler, Semenza, Auricchio, and Prader (1965),and Auricchio, Rubino, Landolt, Semenza, andPrader (1963b). They recognized that lactosemalabsorption was the basis of the clinicalmanifestations of milk intolerance previouslydiagnosed in a number of patients who, two hoursafter milk ingestion, developed abdominal colic,flatulence, and watery diarrhoea. Removal oflactose from the diet brought them rapid relief.Enzyme studies of intestinal biopsy specimensproved the absence of lactase activity in an otherwisemorphologically normal mucosa. These observa-tions have been confirmed by Cuatrecasas, Lock-wood, and Caldwell (1965), Dunphy, Littman,Hammond, Forstner, Dahlqvist, and Crane (1965),Peternel (1965), and McMichael, Webb, andDawson (1965).

It has been pointed out, however, that not alladults with deficient lactase activity had clinicalmanifestations when given lactose. Nor did itsremoval alleviate symptoms in other patients whodespite normal lactase could not take milk withoutdiscomfort. Since signs of milk intolerance hadnot been evident during early childhood, it waspostulated that the lactase-deficient patients hadacquired the defect later in life. There are,however, few observations that would allow arational interpretation of pathogenetic factorsoccurring in older children or adults. A largenumber of diseases of the alimentary tract have now

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Sugar Malabsorptionbeen found to be accompanied by reduced orimpaired disaccharidase activity, but in general thesehave been associated with inflammatory or trophicchanges in the intestinal mucosa, usually reversiblewith improvement of the primary condition. Adecrease in lactase activity from birth to the end ofthe suckling period, and continuing to a low levelin the adult, has been observed in various animals, i.e.the pig, calf, rabbit, and rat, and to some extent in thecat and dog. This, however, does not apply to thehuman species (see above), nor is there any supportfor the concept that feeding large amounts oflactose may lead to an increase of lactase activity, asreported in rats (Girardet, 1965; Cuatrecasas et al.,1965). Genetic aspects have therefore been scru-tinized more closely and their significance stressed.

Racial factors. Of the 41 American Negroesstudied by Cuatrecasas et al. (1965), 30 were lactosenon-absorbers. This high incidence of lactasedeficiency in the American Negro induced Cook andKajubi (1966) to examine its tribal distribution inUganda. They found lactase deficiency to becommon in Baganda children and adults, and alsoamong members of other Bantu tribes. Patientswith Hamitic ancestry from Rwanda and Ankole hadmuch higher levels of activity. Tribal cultures andhabits may have been influenced by lactase levels,since the Hamites studied were cattle owners andlived mainly on milk, whereas the Baganda are anagricultural society who lived mainly on a vegetablediet. The incidence of lactase deficiency in theAmerican Negro was further studied by Bayless andRosenzweig (1966) with 40 healthy, well-nourishedvolunteers. 7000 of the Negroes had low levels ofactivity, compared with 5% of the Caucasians.McMichael et al. (1965, 1966), referring to apersonal communication by Moskoutis regardingthe great frequency of lactase deficiency amongGreeks, point out that 15 out of 17 Greek Cypriotsliving in London whose lactose tolerance was testedalso had lactase deficiency. The experience ofJeejeebhoy, Desai, and Verghese (1964) withpatients suffering from sprue indicates that deficientlactase activity is not uncommon in the Indianpopulation, though this relates to special circum-stances. Its occurrence as a post-gastrectomycomplication transcends racial limits and has mainlybeen reported in Caucasians (Hooft, van Hauwaert,de Laey, and Adriaenssens, 1963; Plotkin andIsselbacher, 1964).

Familial lactose intolerance. Discussions ofthe published material on lactose malabsorptionoften make reference to a syndrome first described

by Durand in 1958 under the title of 'Lattosuriaidiopathica in una paziente con diarrea cronica edacidosi'. He published the biochemical data of thecase in greater detail in 1959. The two paperscontain the case history of a 13-month-old girl ofconsanguineous parents who had recurrent episodesof diarrhoea from the first few days of life, accom-panied by a heavy lactosuria, minor degrees ofproteinuria, renal acidosis, failure to thrive, andeventual death at the age of 15 months. Necropsyshowed an atrophic enteritis with degenerativeatrophic changes in adrenals, liver, and convolutedtubules in the kidney. Among other explanationsDurand suggested the possibility of an intestinallactase deficiency as the cause of the disease.Darling, Mortensen, and S0ndergaard (1960)published records of two related infants sufferingfrom diarrhoea, vomiting, and failure to thrive,associated with lactosuria and aminoaciduria, withdeath at a few weeks of age. Short periods oflactose-free diet had led to the disappearance of themellituria, but did not seem to influence the courseappreciably. A case of congenital lactose intoler-ance in a 2-year-old child with lactosuria, renalacidosis, increase in blood urea, vomiting, andfailure to thrive, was recognized by Fois, Vedovini,and Marinello (1961): recovery followed a lactose-free regimen. Congenital lactosuria occurring as afamilial fatal disease in 3 sibs (Jeune, Charrat,Cotte, Fournier, and Hermier, 1960) illustrates itsgravity. A lactose-free diet ensured recovery in anumber of cases (Fois et al., 1961; Inall andBurkinshaw, 1960; Holzel, Mereu, and Thomson,1962).

It has been suggested that this disorder is a moresevere form of deficient lactase activity and lactosemalabsorption, but our studies lead to the view thatcongenital (familial) lactose intolerance is an entirelydifferent clinical and pathological entity, with aseparate pathogenesis, pathophysiology, and progno-sis. There may be some similarity in symptomato-logy, since a temporary reduction of lactase activitymay be part of some process interfering with themore general absorptive functions and an increasedpermeability of the small intestinal mucosa. Theassociated sucrosuria, glucosuria, and steatorrhoeaare in keeping with such a view. The gastro-intestinal manifestations are mainly vomiting andonly to a lesser extent diarrhoea; renal involvementcan be deduced from the presence of acidosis,aminoaciduria, mellituria, and a rise in blood urea.Haemorrhagic complications are not unusual in theuntreated patient whose condition is precarious.The disease is self-limiting, and tolerance for

lactose may return 6-18 months after the onset.

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Too early resumption of milk feeding may end incatastrophe.The reasons for regarding 'familial lactose intol-

erance' as a separate entity are: (1) difference inclinical pattern; (2) the presence of lactosuria whichis absent in even the severe forms of deficientlactase activity; (3) the satisfactory rise in bloodglucose levels following lactose-loading doses duringthe active phase of the disease (Darling et al., 1960;Fois et al., 1961; Holzel et al., 1962); (4) the returnto normal lactose absorption after brief periods oflactose-free diet, with exacerbation of lactoseintolerance if lactose feeding continues; (5) theself-limiting nature of the disorder, hardly compa-tible with a hereditary enzyme defect; and (6)lactase activity demonstrated to be normal afterrecovery (Holzel, 1967).

Primary Sucrase-Isomaltase DeficiencyThe description by Weijers et al. (1961) of a

diarrhoeal disorder in children due to sucrosemalabsorption was soon followed by others.Prader, Auricchio, and Murset (1961), Delaitre,Fonty, Varlet, and Fourrier (1961), Auricchio et al.(1961), Auricchio, Dahlqvist, Miirset, and Prader(1962), and Auricchio, Dahlqvist, Murset, andPrader (1963a), Auricchio, Rubino, Prader, Rey, Jos,Freza], and Davidson (1965b) demonstrated thesimultaneous occurrence of isomaltase deficiency intheir patients, and this was confirmed by investigatorsin different parts of the globe (Anderson, Messer,Townley, and Freeman, 1963; Rey, Frezal, Jos,Bauche, and Lamy, 1963; Burgess, Levin,Mahalanabis, and Tonge, 1964; Launiala,Perheentupa, Visakorpi, and Hallman, 1964; Nordioand La medica, 1964; Sonntag, Brill, Troyer, Welsh,Semenza, and Prader, 1964; Townley, Khaw, andShwachman, 1965; Semenza, Auricchio, Rubino,Prader, and Welsh, 1965b).

In recent reviews of the condition, the number ofpublished cases has been given as 40 by Townley(1966), while Prader and Auricchio (1965) know of63 cases, 34 male and 29 female, among them only5 adults.

Genetics. The mode of inheritance has yet tobe established. A dominant trait was initiallysuggested (Auricchio et al., 1961), but a recessivedisorder seems probable, since there are at least 10records of affected sibs and 2 of consanguineousparents (Prader and Auricchio, 1965). One of thedifficulties in establishing the recessive nature of thecondition is the recognition of the heterozygote.Kerry and Townley (1965) decided to use thequantitative assay of disaccharidase in small bowelbiopsy specimens for the detection of the carrier of

the abnormal gene. Four families, each with achild suffering from sucrose-isomaltose absorption,were submitted to peroral intestinal biopsies, andthe values of the disaccharidase assay were comparedwith those obtained in a group of normal adults andchildren. All the parents of the affected childrenhad intestinal sucrase and isomaltase levels belowthe average found in the control group. When thelevels of the enzymes were expressed as ratios tolactose they differed significantly from the controlgroup. The authors therefore concluded thatsucrase-isomaltase deficiency was a recessively-transmitted disorder.A special problem in this hereditary condition is

the constant association of two enzyme defects.According to Dahlqvist (1962) the two activities areattributable to separate enzymes. To reconcile theavailable facts with the 'one gene one enzymehypothesis', is somewhat puzzling. However, if itbe assumed that one defective structural elementmay possess two active side chains for differentsubstrates this would readily explain the data(Launiala et al., 1964).

Clinical features. Diarrhoea, the most con-stant symptom in all the sugar malabsorptionsyndromes, follows the introduction of sucrose andstarch into the infant's diet. In the breast-fedinfant this is likely to be at a later date than in thebottle-fed one. Though many of the commerciallyprepared baby foods contain only lactose, starch isnow being offered at an increasingly early age. Thepersistence of the fermentative diarrhoea is accom-panied by a failure to thrive, which is never asmarked as in the cases with lactase deficiency.Some patients manifest also minor degrees ofsteatorrhoea (Nordio, La medica, and Vignolo, 1961;Anderson et al., 1963; Francois, Frederich, Vicens-Calvet, Bertrand, and Ruitton-Ugliengo, 1963; Reyet al., 1963; Gorouben, Bedu, Le balle, Grumbach,Yonger, Weill, and Kaplan, 1963; Burgess et al.,1964; Lifshitz and Holman, 1964). Spontaneousimprovement has been known to occur (Auricchioet al., 1961), but in the vast majority of patientsdietary adjustment, such as the replacement ofsucrose and starch by glucose, is enough to bringabout lasting improvement.

Diagnosis of Disaccharidase DeficienciesThis should be considered whenever there is a

history of diarrhoea, with onset in early infancy.Marked malnutrition will only be encountered in themore severe forms and is more likely to be the resultof lactase deficiency than of defective sucrase andisomaltase activity. The frothy appearance of the

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Sugar Malabsorptionstools and their sour smell may arouse the firstsuspicion of such a disorder.

Faecal pH. The faecal pH can be used as ascreening test, but is not very reliable since it mayalso be lowered in infective forms of gastro-enteritis, and may occasionally be normal. In serialstool examination on several adult patients withhypolactasia, McMichael et al. (1965) found that thepH fluctuated, and that not even after lactoseadministration was a low value registered. Valueswere similar to those found in 14 control patients,and in no patient was a random pH of less than 5 - 7recorded. However, in infants on cows' milk feedsthe stool has a pH between 6 * 5 and 7 * 5, while in thefermentative diarrhoeas it is below 6 and sometimescloser to 5.

Lactic acid in faeces. Since the fall in pH isthe result of the formation of large quantities of lowmolecular weight organic acids, the estimation oflactic acid has been recommended as a useful test.Lactic acid can be determined by enzymatic orchemical methods; a simple technique has beendeveloped by Clarke and Podmore (1966).Although increase in lactic acid excretion may

occur in other forms of diarrhoea, and cannot there-fore be regarded as specific, a healthy child on anormal diet rarely excretes more than 35 mg. lacticacid per 24 hours. By contrast, in a fermentativediarrhoea several grammes may be excreted in thecourse of 24 hours (Weijers and van de Kamer,1964), and the finding of more than 50 mg. lacticacid in a random sample of 100 g. faeces can betaken to indicate excess fermentation.

Determination of the total content of low molecu-lar weight volatile fatty acids (Weijers and van derKamer, 1964) provides no more reliable evidencethan the tests mentioned; no increase was found inlactase-deficient adults (McMichael et al., 1965).

Sugar-loading tests. If carried out in theabsence of diarrhoea, these tests are extremely usefulin the assessment of disaccharidase activity. Therecommended dose of sugar administered orally is2 g./kg. body weight or 50 g./m.2 body surface area.It makes little difference which of the two standardsone accepts, provided it is maintained. It seemsadvisable to precede the test for a few days with adiet rich in carbohydrates. Since absorption isinfluenced by a variety of factors besides disacchari-dase activity, as for instance the rate of gastricemptying, the standard use of a 10% solution of therequired sugar is probably wise (Girardet, 1965).In some adults slow gastric emptying may lead to a

flat lactose tolerance curve, and Kern and Struthers(1966) found that in these cases the intraduodenaladministration of 30 g. lactose in 300 ml. water in30 minutes caused a normal rise of blood glucose.Peternel (1965), in evaluating the oral lactosetolerance test as a screening test, found a goodcorrelation between an increase in blood glucosegreater than 20 mg./100 ml. above the fasting level,with normal lactase activity. Girardet and Richte-rich (1962) failed to obtain a rise in glucose bloodlevels in some healthy adults after lactose loading,and this may occasionally happen. In our experi-ence, lactose tolerance tests can be usefully employediftheir results are reproducible. To a large measure,this applies also to other disaccharide loading tests,in particular to sucrose tolerance tests. An increaseof blood glucose of more than 30 mg./100 ml. abovefasting level at any point of the tolerance curve maybe regarded as an indication ofnormal disaccharidaseactivity, values that do not exceed 20 mg. usuallydenoting impaired absorption. An increase of20-30 mg./100 ml. above fasting level is of doubtfulsignificance.

It is important to carry out control tests with thecorresponding component monosaccharides mixedin equal parts to eliminate disturbances with similarsymptomatology but different pathogenesis, such asthe glucose-galactose malabsorption syndromes, orconditions associated with a gross general reductionof small intestinal absorptive capacity. Congenitalmonosaccharide malabsorption has not been reportedin adults and the control tests have therefore lesssignificance. Fat balance studies, xylose excretion,etc. have to be employed to excJude disaccharidasedeficiencies secondary to other causes of mal-absorption (Anderson, 1966).

Sugar excretion in the urine. Excluding theminute quantities that occur physiologically, this isnot raised in the primary disaccharidase deficiencies,but is present to an appreciable degree in lactoseintolerance (see above). The faeces, however, maycontain increased amounts of the disaccharide or,under special bacteriological conditions, also themonosaccharides. Chromatographic demonstrationof the sugars in the faeces and urine may prove avaluable diagnostic aid. Application of the 'clini-test' to the liquid part of the motions was suggestedas a helpful screening procedure in cases suspectedof disaccharide malabsorption by Burke, Kerry, andAnderson (1965).

Radiological diagnosis. Recently an attempthas been made to exploit radiography in the recogni-tion of sugar malabsorption, by utilizing a suspen-

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sion of micropaque barium sulphate with 25 g. oflactose or other sugars, according to the suspectedenzyme deficiency. Laws and Neale (1966) foundcharacteristic changes: the small intestine appeareddistended by dilute contrast medium; peristalsiswas very active, the contrast medium reaching thetransverse or descending colon within an hour;while the haustral pattern was strikingly prominent.

Quantitative biochemical assay of disaccharidasesin peroral biopsy specimens of intestinal mucosa isregarded as the most reliable diagnostic means.The technique, difficulties, and limitations of peroralbiopsy have been very fully discussed by Anderson(1966). Since only a tiny fraction of intestinalmucosa is examined, one may obtain entirelymisleading information, particularly in disacchari-dase deficiencies secondary to diseases of the smallgut. In conditions where the proximal part is moreheavily involved than the distal, one may be facedwith the conflicting results of tolerance tests andenzyme assay, namely that disaccharide absorptionmay be taking place even in the seemingly completeabsence of the sugar-splitting enzymes. Alterna-tively, a variety of agents may temporarily inhibitenzyme activity, but the resulting sugar malabsorp-tion may be only one minor consequence of anunderlying gross inflammatory process.

Prader and Auricchio (1965) give the followingfigures for the disaccharidase activities in themucosa of the jejunum of the adult obtained bybiopsy (Table II). The enzyme activity is expres-sed in units per g. protein; each unit splits onemicromole substrate per minute.

TABLE IIDisaccharide Activity in Jejunal Mucosa inNormal Adults (Prader and Auricchio, 1965)

Enzyme Activity (units/g. protein)Disaccharidase

Mean Range

Maltase .593 310-1120Sucrase .173 70-325Isomaltase .159 65-268Lactase .107 39-258Cellobiase .14 9-21

These authors also point out that though there isgreat variation in the absolute values of disacchari-dase activity, the ratios between the various enzymesare constant with the exception of lactase activity.Maltase activity is three to four times higher thansucrase or isomaltase, and the latter about three tofour times higher than lactase activity. Burke et al.(1965) gave the normal range of disaccharidaseactivity in jejunal mucosa in children (Table III).

TABLE IIIDisaccharide Activity (units/g. protein) in

Jejunal Mucosa in Normal Children(Burke et al., 1965)

Lactase Sucrase Isomaltase Maltase

IIRange 1 4-132 32-228 31-177 83-615Mean 49 95 89 260

Burgess et al. (1964) expressed the unit of enzymeactivity as equal to the hydrolysis in ,umole ofsubstrate/g. wet mucosa per minute; the values ob-tained in normal children are given in Table IV.Choosing the same standard, Holzel (1966) foundthe values ranging for lactase, 5-12; for maltase,34-70; and for sucrase, 7-21. Recently Messer andDahlqvist (1966) described a one-step ultramicromethod for the assay of intestinal disaccharidases,which is more suitable for the small quantities ofmucosa removed by peroral biopsy than the two-step method originally developed by Dahlqvist(1964a, b).

TABLE IVDisaccharide Activity (units/g. wet mucosa perminute) in Jejunal Mucosa in Normal Children

(Burgess et al., 1964)Lactase Maltase Sucrase

Range 7-12 43-90 12-20Mean 8 -7 62 -6 17 *4

Acquired Disaccharide MalabsorptionWith the knowledge that the disaccharidases were

located in the exposed position of the brush-borderof the mucosal epithelium, intensive investigationof all those disorders associated with structuralchanges of the intestinal mucosa for sugar mal-absorption has revealed a large number of secondarydisaccharidase deficiencies, both in children andadults. Lactase was far more commonly deficientthan other disaccharidases, particularly amongstadults. In children, reduced or absent activityrelated often to two or even three of the hydrolyticenzymes.

Secondary lactase deficiency in adults (Haemmerliet al., 1965) has been encountered following gastro-jejunostomy (Gryboski, Thayer, Gryboski, Gabriel-son, and Spiro, 1963), bowel resection (Kern,Struthers, and Attwood, 1963), and various otheraffections of the gut. Combined disaccharidasedeficiences were common in coeliac disease of theadult (Plotkin and Isselbacher, 1964). In children,

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Sugar Malabsorptionthe most striking form of deficient disaccharidaseactivity is associated with gluten-induced entero-pathy (Holzel, 1964; Shmerling, Auricchio, Rubino,Hadorn, and Prader, 1964; Nordio, La medica,Vignolo, and Berio, 1965; Arthur, Clayton, Cottom,Seakins, and Platt, 1966; Lubos, Gerrard, andBuchan, 1967). Our studies and those of otherworkers agree on the fact that during the florid phaseof the illness, when the surface structures of thesmall intestinal mucosa are considerably disor-ganized, disaccharide absorption is grossly impaired.Lactose tolerance is much more reduced than that ofother disaccharides, and malabsorption of this sugarpersists for much longer than that of the othercommon disaccharides. Patients with inadequatedietary control, and in relative well-being thoughwith some delay in growth, have been able toabsorb glucose at a normal rate but have shown flatdisaccharide tolerance curves. It seems, therefore,that disaccharide loading tests can be used as afurther tool in the assessment of absorptive recovery.The occurrence of crises has in some of our coeliacpatients been related to an increased intake oflactose. In one patient, enzyme assay of theintestinal mucosa specimen showed almost completeabsence of lactase activity. A lactose- and gluten-free diet led to elimination of the crises anduninterrupted progress towards recovery. The rou-tine imposition of lactose-, sucrose- and gluten-freediets (Arthur et al., 1966) on every child withcoeliac disease may place an unnecessarily heavyburden on hospital and home, but where a gluten-free diet alone does not achieve the desired result,removal of the disaccharides may hasten recovery.The disacchariduria in these patients (Arthur et al.,1966) is more likely an expression of the severity ofmucosal damage than an index of disaccharideintolerance (Prader, Shmerling, and Hadorn,1966).

Kwashiorkor. Protein-calorie malnutrition isanother disorder that includes in its symptomcomplex severe and often persisting diarrhoea.Bowie, Brinkman, and Hansen (1965) demonstratedthat children suffering from the condition couldabsorb monosaccharides satisfactorily, but seemedintolerant of disaccharides; exclusion from the dietresulted in control of the diarrhoea. Cook and Lee(1966), in an attempt to assess the degree of recoveryof disaccharidase activity, examined 7 Baganda and13 Bahutu children 4-10 years after diagnosis andtreatment of kwashiorkor. Lactase levels in 18biopsy specimens were low. Lactase deficiency wasconfirmed in 17 children by tolerance tests. Allother disaccharidases were within normal limits.

Giardiasis. Lactose malabsorption in heavyinfestation with Giardia intestinalis has been recor-ded by Durand (1964), Nordio, La medica, andVignolo (1963), and Holzel (1967). Depres-sion of lactase activity may occur as an isolatedphenomenon, or as part of the more general reduc-tion of disaccharidase activity. Mucosal biopsy inour cases showed only minor degrees of inflamma-tory reaction with no major alteration in the mucosalpattern. Eradication of the infection was followedby very slow recovery of enzyme function.

Gastro-enteritis. Intolerance to milk followinginfective forms of gastro-enteritis was known to thepaediatricians of the early decades of this century,but the protein and fat constituents were thenregarded as causing the damage. Sunshine andKretchmer (1964) and Burke et al. (1965) producedlaboratory evidence that dietary lactose was thenoxious factor in the persistent diarrhoea in these,cases.

Monosaccharide Malabsorption

It is not unknown for the same importantscientific observation to be made by independentscientific workers at the same time in different partsof the world. Preoccupation with similar topics ofresearch is a common feature in the Western nationsand probably more the result of modern means ofcommunication than of the influence of a geniusmundi.

It is nevertheless interesting to record thatLindquist, Meeuwisse, and Melin (1962) andLindquist and Meeuwisse (1962) in Swedenrecognized a new disorder of monosaccharidemalabsorption more or less simultaneously with theFrench authors, Laplane, Polonovsky, Etienne,Debray, Lods, and Pissarro (1962). It was rightlynamed glucose-galactose malabsorption by Lind-quist and his colleagues, who realized that basicallyit was probably due to some major disturbance ofthe absorptive mechanism, and they, as well as theFrench workers, assumed a congenital disturbanceof the active transfer mechanism. Since thenfurther cases have been published in Germany(Linneweh, Schauml6ffel, and Barthelmai, 1965),Australia (Anderson, Kerry, and Townley, 1965),U.S.A. (Schneider, Kinter, and Stirling, 1966;Marks, Norton, and Fordtran, 1966), and Belgium(Eggermont and Loeb, 1966). At least 11 well-documented cases prove the wide distribution ofthis inborn error of metabolism; familiarity with itsclinical manifestation will in due course lead to atrue assessment of its incidence.

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350 A. HolzelClinical picture. There is severe watery

diarrhoea starting in the first week of life, leading torapid and life-threatening dehydration. The faecescontain large quantities of sugars and lactic acid;the urine may also contain reducing substances insmall amounts. The gravity of the conditionvaries; it may cause death in the untreated, or if lesssevere may produce a severe marasmus accompaniedby chronic diarrhoea. The most telling feature isprobably the almost instantaneous cessation of theexplosive diarrhoea when oral feeds are stopped,only to start again if foods containing monosacchar-ides other than fructose or disaccharides are given,which by hydrolysis lead to the breakdown tomonosaccharides. Familial incidence was observedby Lindquist et al. (1962), Laplane et al. (1962), andAnderson et al. (1965). Routine laboratory in-vestigations of the faeces for pathogens are generallyunhelpful. Slight steatorrhoea was observed in onepatient only. A glucose or galactose loading testdid not produce an adequate rise in blood glucoselevels, in contrast to fructose which caused anincrease of both glucose and fructose in the blood.Dehydration was associated with disturbances ofelectrolyte and nitrogen balance. Peroral biopsyspecimen showed normal disaccharidase activity,and seemed structurally normal.

In view of the tolerance for fructose, with itsdifferent mode of absorption, it was a fair assump-tion that the active carrier system might be at fault,and a good deal ofevidence has been brought forwardin its support. Loading tests with 3-0-methylglu-cose (Anderson et al., 1965), a synthetic sugar withthe requisite configuration for active transport,showed failure of absorption. The application ofautoradiography to fresh specimens of intestinalmucosa with 14C-labelled galactose in a specialmedium, demonstrated the inability of the cells ofthe patient's mucosa to accumulate the galactose,while the uptake succeeded in the control specimen.Eggermont and Loeb (1966) tried to prove thatglucose-galactose malabsorption was the result of aderangement of the sodium-dependent activetransport. Meeuwisse and Dahlqvist (1966) ob-tained intestinal biopsy specimens from 2 patientswith this disorder. The mucosa appeared normalon light microscopy. On incubation of thespecimens with 14C-labelled glucose there was nogreater accumulation of the sugar in the tissue thanin the medium, while in control experimentsglucose in the mucosa was 4 times as high as that inthe medium. They are also of the opinion that thedefect is in the glucose-galactose specific carrier.In a special study with 14C-labelled sugars,Linneweh, Schauml6ffel, Graul, and Bode (1966)

succeeded in determining the residual enzymeactivity in their patient with monosaccharide mal-absorption; it was 7 6% for glucose and 4 6% forgalactose. Dietary treatment can be successfullycarried out with a formula consisting of casein, cornoil, and fructose, with adequate vitamin comple-ments. A rather ill-defined form ofmonosaccharidemalabsorption of a transitory nature in younginfants has recently been reported from Australia(Burke and Danks, 1966). Although these babieswere thoroughly investigated, the results did notallow any aetiological or pathogenetic conclusions.

The rapidly expanding knowledge of the enzy-matic mechanism involved in sugar absorption andits disturbances has by no means reached its limits,and no doubt further development will add to abetter understanding of the physiological processesinvolved.

REFERENcESAnderson, C. M. (1966). Intestinal malabsorption in childhood.

Arch. Dis. Childh., 41, 571.-, Kerry, K. R., and Townley, R. R. W. (1965). An inborn

defect of intestinal absorption of certain monosaccharides.ibid., 49, 1.

-, Messer, M., Townley, R. R. W., and Freeman, M. (1963).Intestinal sucrase and isomaltase deficiency in two siblings.Pediatrics, 31, 1003.

Arthur, A. B., Clayton, B., Cottom, D. G., Seakins, J. W. T., andPlatt, J. W. (1966). Importance of disaccharide intolerance inthe treatment of coeliac disease. Lancet, 1, 172.

Auricchio, S., Dahlqvist, A., Murset, G., and Prader, A. (1962).Intestinal isomaltase deficiency in patients with hereditarysucrose and starch intolerance. ibid., 1, 1303.

and- (1963a). Isomaltose intolerance causingdecreased ability to utilize dietary starch. J. Pediat., 62, 165.

-, Prader, A., Murset, G., and Witt, G. (1961). Saccharosein-toleranz. Durchfall infolge hereditiren Mangels an intestinalerSaccharaseaktivitat. Helv. paediat. Acta, 16, 483.

-, Rubino, A., Landolt, M., Semenza, G., and Prader, A. (1963b).Isolated intestinal lactase deficiency in the adult. Lancet, 2,324.

-,-, and Murset, G. (1965a). Intestinal glycosidase activitiesin the human embryo, foetus and newbom. Pediatrics, 35, 944.

-,,- , Prader, A., Rey, J., Jos, J., Frezal, J., and Davidson, M.(1965b). Intestinal glycosidase activities in congenital mal-absorption of disaccharides. J. Pediat., 66, 555.

-, Semenza, G., and Rubino, A. (1965c). Multiplicity of humanintestinal disaccharidases. II. Characterization ofthe individualmaltases. Biochim. biophys. Acta (Amst.), 96, 498.

Bayless, T. M., and Rosenzweig, N. S. (1966). Lactase deficiencyin Uganda. Lancet, 2, 225.

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Bowie, M. D., Brinkman, G. L., and Hansen, J. D. L. (1965).Acquired disaccharide intolerance in malnutrition. J. Pediat.,66, 1083.

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Burkinshaw, J. H. (1960). Lactosuria and sucrosuria with failureto thrive. Proc. roy. Soc. Med., 53, 318.

Cajori, F. A. (1933). The enzyme activity of dogs' intestinal juiceand its relation to intestinal digestion. Amer. J. Physiol., 104,659.

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mination of lactic acid in faeces in glycosidase deficiency.Clin. chim. Acta, 13, 725.

Cook, G. C., and Kajubi, S. K. (1966). Tribal incidence of lactasedeficiency in Uganda. Lancet, 1, 725.

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intestinal disaccharidases and hereditary disaccharide intoler-ance. The hydrolysis of sucrose, isomaltose, palatinose(isomaltulose) and a 1, 6-a-oligosaccharide (iso-malto-oligosaccharide) preparation. J. clin. Invest., 42, 556.

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Darling, S., Mortensen, O., and Smndergaard, G. (1960). Lactosuriaand amino-aciduria in infancy. A new inborn error of meta-bolism? Acta paediat. (Uppsala), 49, 281.

Davenport, H. W. (1966). Physiology of the Digestive Tract, 2nded. Year Book Medical Publishers, Chicago.

Davidson, M., Sobel, E. H., Kugler, M. M., and Prader, A. (1964).Intestinal lactase deficiency of presumed congenital origin intwo older children (Abstr.). Gastroenterology, 46, 737.

Delaitre, R., Fonty, Varlet, and Fourrier (1961). Diarrh6echronique chez un nourrisson par intolerance au saccharose.Arch. franc. Pidiat., 18, 1202.

Doell, R. G., and Kretchmer, N. (1962). Studies of small intestineduring development. I. Distribution and activity of j3-galactosidase. Biochim. biophys. Acta (Amst.), 62, 353.

-, and- (1964). Intestinal invertase: precocious develop-ment of activity after injection of hydrocortisone. Science,143, 42.

-, Rosen, G., and Kretchmer, N. (1965). Immunochemicalstudies of intestinal disaccharidases during normal and pre-cocious development. Proc. nat. Acad. Sci. (Wash.), 54, 1268.

Dunphy, J. V., Littman, A., Hammond, J. B., Forstner, A.,Dahlqvist, A., and Crane, R. K. (1965). Intestinal lactasedeficit in adults. Gastroenterology, 49, 12.

Durand, P. (1958). Lattosuria idiopatica in una paziente condiarrea cronica ed acidosi. Minerva pediat., 10, 706.

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Defective Carbohydrate Digestion and Absorption, ed. P. Durand,p. 105. I1 Pensiero Scientifico, Rome.

-, and La medica, J. M. (1962). Disaccharide intolerance.Helv. paediat. Acta, 17, 395.

Eggermont, E., and Loeb, H. (1966). Glucose-galactose intoler-ance. Lancet, 2, 343.

Eichholz, A., and Crane, R. K. (1965). Studies on the organizationof the brush border in intestinal epithelial cells. I. Trisdisruption of isolated hamster brush borders and densitygradient separation of fractions. J. Cell. Biol., 26, 687.

Fois, A., Vedovini, F., and Marinello, E. (1961). Intoleranzacongenita al lattoso. Minerva pediat., 13, 297.

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Fridhandler, L., and Quastel, J. H. (1955). Absorption of sugarsfrom isolated surviving intestine. Arch. Biochem., 56, 412.

Girardet, P. (1965). Absorption et Malabsorption du Lactose.H. Huber, Berne and Stuttgart.

-, and Richterich, R. (1962). A propos de l'alactasie congenitaleet des courbes de surcharge au lactose. Ann. paediat. (Basel),198, 127.

Gorouben, J. C., Bedu, J., Le balle, J. C., Grumbach, R., Yonger,J., Weill, J., and Kaplan, M. (1963). L'intolerance ausaccharose. Etude clinique et biologique de 5 cas. Arch.franc. Pediat., 20, 253.

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Greaves, J. P., and Hollingsworth, D. F. (1964). Changes in thepattern of carbohydrate consumption in Britain. Proc. Nutr.Soc., 23, 136.

Gryboski, J. D., Thayer, W. R., Jr., Gryboski, W. A., Gabrielson,I. W., and Spiro, H. W. (1963). A defect in disaccharidemetabolism after gastrojejunostomy. New Engl. J. Med., 268,78.

Haemmerli, U. P., Kistler, H. J., Ammann, R., Auricchio, S., andPrader, A. (1963). Lactasemangel der Dusmdarmmucosa alsUrsache gewisser Formen erworbener Milchintoleranz beimErwachsenen. Helv. med. Acta, 30, 693.

Marthaler, T., Semenza, G., Auricchio, S., andPrader, A. (1965). Acquired milk intolerance in the adultcaused by lactose malabsorption due to a selective deficiency ofintestinal lactase activity. Amer. J. Med., 38, 7.

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Holzel, A. (1962). Alactasia. In Erbliche Stoffwechselkrankheiten:Genetic Defects of Biologically Active Proteins, ed. P. Linneweh,p. 219. Urban & Schwarzenberg, Munich.- (1964). Nutritional consequences of altered carbohydrate

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relation to diarrhoea. Pediat. Clin. N. Amer., 12, 635.(1966). Disaccharide malabsorption and disaccharide

intolerance in childhood. In Postgraduate Gastro-enterology,ed. T. J. Thomson and I. E. Gillespie, p. 68. Bailliere,Tindall & Cassell, London.(1967). Disorders of carbohydrate metabolism. J. roy. Coll.Phycns (Lond.), 1, 177.(1967). Disaccharide intolerances. Symposium on disordersof carbohydrate metabolism. Proc. of Society for the Study ofInborn Errors of Metabolism. In the press.

-, Mereu, T., and Thomson, M. L. (1962). Severe lactoseintolerance in infancy. Lancet, 2, 1346., Schwarz, V., and Sutcliffe, K. W. (1959). Defective lactoseabsorption causing malnutrition in infancy. ibid., 1, 1126.

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Lindquist, B., and Meeuwisse, G. W. (1962). Chronic diarrhoeacaused by monosaccharide malabsorption. Acta paediat.(Uppsala), 51, 674., -, and Melin, K. (1962). Glucose-galactose malabsorp-tion. Lancet, 2, 666.

Linneweh, F., Schaumloffel, E., and Barthelmai, W. (1965).Angeborene Glukose- und Galaktose-Malabsorption. Klin.Wschr., 43, 405.-,-, Graul, E. H., and Bode, H. H. (1966). OYber dieRestaktivitat defekter Enzyme bei hereditarer Mono- undDisaccharid-Malabsorption. Schweiz. med. Wschr., 96, 424.

Littman, A., and Hammond, J. B. (1965). Diarrhea in adultscaused by deficiency in intestinal disaccharidases. Gastro-enterology, 48, 237.

Lubos, M. C., Gerrard, J. W., and Buchan, D. J. (1967). Disac-charidase activities in milk-sensitive and celiac patients. 7.Pediat., 70, 325.

McMichael, H. B., Webb, J., and Dawson, A. M. (1965). Lactasedeficiency in adults: a cause of "functional" diarrhoea. Lancet,1, 717., -, and - (1966). Jejunal disaccharidases and someobservations on the cause of lactase deficiency. Brit. med. J7.,2, 1037.

Marks, J. F., Norton, J. B., and Fordtran, J. S. (1966). Glucose-galactose malabsorption. J. Pediat., 69, 225.

Meeuwisse, G., and Dahlqvist, A. (1966). Glucose-galactosemalabsorption. Lancet, 2, 858.

Messer, M., and Dahlqvist, A. (1966). A one-step ultramicromethod for the assay of intestinal disaccharidases. Analyt.Biochem., 14, 376.

Miller, D., and Crane, R. K. (1961). The digestive function of theepithelium of the small intestine. I. An intracellular locus ofdisaccharide and sugar phosphate ester hydrolysis. Biochim.biophys. Acta (Amst.), 52, 281.

Newcomer, A. D., and McGill, D. B. (1966). Distribution ofdisaccharidase activity in the small bowel of normal andlactase-deficient subjects. Gastroenterology, 51, 481.

Nordio, S., and La medica, G. M. (1964). In Disorders Due toIntestinal Defective Carbohydrate Digestion and Absorption,ed. P. Durand, p. 142. Il Pensiero Scientifico, Rome.- , and Vignolo, L. (1961). Un caso di diarrea cronica

connatale da intolleranza a saccarosio ed alle destrine. Minervapediat., 13, 1766., -, and - (1963). Diarree croniche da intolleranzealimentari. Intolleranze ai carboidrati e sindrome celiaca.ibid., 15, 1425.- , -, and Berio, A. (1965). Six cases of lactose intoler-ance. Lactose intolerance and coeliac disease. Disaccharidasesactivity in the intestinal mucosa ascertained with the peroralbiopsy. Ann. paediat. (Basel), 204, 3.

Overton, J., Eichholz, A., and Crane, R. K. (1965). Studies on theorganization of the brush border in intestinal epithelial cells.II. Fine structure of fractions of Tris-disrupted hamsterbrush borders. J. cell Biol., 26, 693.

Peternel, W. W. (1965). Lactose tolerance in relation to intestinallactase activity. Gastroenterology, 48, 299.

Plotkin, G. R., and Isselbacher, K. J. (1964). Secondary disac-charidase deficiency in adult celiac disease (nontropical sprue)and other malabsorption states. New Engl. J. Med., 271, 1033.

Prader, A., and Auricchio, S. (1965). Defects of intestinal disac-charide absorption. Ann. Rev. Med., 16, 345.- , and Murset, G. (1961). Durchfall infolge hereditaren

Mangels an intestinaler Saccharaseakivitat (Saccaroseintoleranz).Schweiz. med. Wschr., 91, 465.

-, Shmerling, D. H., and Hadorn, B. (1966). Disaccharides andceliac disease. Lancet, 1, 435.

Rey, J., Frezal, J., Jos, J., Bauche, P., and Lamy, M. (1963)Diarrhee par trouble de l'hydrolyse intestinale du saccharose, dumaltose et de l'isomaltose. Arch. franc. Pediat., 20, 381.

Schneider, A. J., Kinter, W. B., and Stirling, C. E. (1966). Glucose-galactose malabsorption. New Engl. J. Med., 274, 305.

Semenza, G., Auricchio, S., and Rubino, A. (1965a). Multiplicityof human intestinal disaccharidases. I. Chromatographicseparation of maltases and of two lactases. Biochim. biophys.Acta (Amst.), 96, 487.

-, -, -, Prader, A., and Welsh, J. D. (1965b). Lack ofsome intestinal maltases in a human disease transmitted by asingle genetic factor. ibid., 105, 386.

-, Tosi, R., Vallotton-Delachaux, M. C., and Mulhaupt, E.(1964). Sodium activation of human intestinal sucrase and itspossible significance in the enzymic organization of brushdisorders. ibid., 89, 109.

Shmerling, D. H., Auricchio, S., Rubino, A., Hadom, B., andPrader, A. (1964). Der sekundire Mangel an intestinalerDisaccharidaseaktivitat bei der Coliakie. Quantitative Bestim-mung der Enzymaktivitat und klinische Beurteilung. Helv.paediat. Acta, 19, 507.

Sonntag, W. M., Brill, M. L., Troyer, W. G., Jr., Welsh, J. D.,Semenza, G., and Prader, A. (1964). Sucrose-isomaltosemalabsorption in an adult woman. Gastroenterology, 47, 18.

Sunshine, P., and Kretchmer, N. (1964). Studies of small intestineduring development. III. Infantile diarrhea associated withintolerance to disaccharides. Pediatrics, 34, 38.

Thornton, A. A., Burkinshaw, J. H., and Kawerau, E. (1962).Chronic diarrhoea relieved by lactose-free diet. Proc. roy.Soc. Med., 55, 979.

Townley, R. R. W. (1966). Disaccharidase deficiency in infancy andchildhood. Pediatrics, 38, 127.

-, Khaw, K. T., and Shwachman, H. (1965). Quantitativeassay of disaccharidase activities of small intestinal mucosalbiopsy specimens in infancy and childhood. ibid., 36, 911.

Weijers, H. A., and van de Kamer, J. H. (1964). Fermentativediarrhoeas. In Disorders Due to Intestinal Defective Carbo-hydrate Digestion and Absorption, ed. P. Durand, p. 59. Grune& Stratton, New York.

-, - , Dicke, W. K., and Ijsseling, J. (1961). Diarrhoeacaused by deficiency of sugar splitting enzymes. I. Actapaediat. (Uppsala), 50, 55.

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