Xq28-Linked Noncompaction of the Left VentricularMyocardium: Prenatal Diagnosis and PathologicAnalysis of Affected Individuals

Steven B. Bleyl,1 Brian R. Mumford,1 Mary-Carole Brown-Harrison,2 Luciana T. Pagotto,2John C. Carey,2 Theodore J. Pysher,2,3 Kenneth Ward,1 and Thomas K. Chin2*1Department of Obstetrics and Gynecology, University of Utah School of Medicine, Salt Lake City2Department of Pediatrics, University of Utah School of Medicine, Salt Lake City3Department of Pathology, University of Utah School of Medicine, Salt Lake City

Isolated noncompaction of the left ventricu-lar myocardium (INVM) is characterized bythe presence of numerous prominent tra-beculations and deep intertrabecular re-cesses within the left ventricle, sometimesalso affecting the right ventricle and inter-ventricular septum. Familial occurrence ofthis disorder was described previously. Wepresent a family in which 6 affected indi-viduals demonstrated X-linked recessive in-heritance of this trait. Affected relativespresented postnatally with left ventricularfailure and arrhythmias, associated withthe pathognomonic echocardiographic find-ings of INVM. The usual findings of Barthsyndrome (neutropenia, growth retarda-tion, elevated urinary organic acids, lowcarnitine levels, and mitochondrial abnor-malities) were either absent or found incon-sistently. Fetal echocardiograms obtainedbetween 24–30 weeks of gestation in 3 of theaffected males showed a dilated left ven-tricle in one heart, but were not otherwisediagnostic of INVM in any of the cases. Fourof the affected individuals died during in-fancy, one is in cardiac failure at age 8months, and one is alive following cardiactransplant at age 9 months. The hearts frominfants who died or underwent transplanta-tion appeared, on gross examination, to beenlarged, with coarse, deep ventricular tra-beculations and prominent endocardial fi-broelastosis. Histologically, there wereloosely organized fascicles of myocytes insubepicardial and midmyocardial zones of

both ventricles, and the myocytes showedthin, often angulated fibers with prominentcentral clearing and reduced numbers offilaments. Markedly elongated mitochon-dria were present in some ventricular myo-cytes from one specimen, but this findingwas not reproducible. Genetic linkageanalysis has localized INVM to the Xq28 re-gion, where other myopathies with cardiacinvolvement have been located. Am. J. Med.Genet. 72:257–265, 1997. © 1997 Wiley-Liss, Inc.

KEY WORDS: X-linked cardiomyopathy;Barth syndrome; myotubular(centronuclear) myopathy;isolated noncompaction ofventricular myocardium; en-docardial fibroelastosis

INTRODUCTION

Cardiomyopathy without structural anomalies of theheart affects approximately 1 in 10,000 infants [Ferenzand Neill, 1992]. Over 20% of dilated cardiomyopathiesare familial [Dec and Fuster, 1994], and three familialmyopathies with cardiac involvement cluster in theXq28 region: Barth syndrome, Emery-Dreifuss muscu-lar dystrophy, and myotubular (centronuclear) myopa-thy (MTM).

Isolated noncompaction of the ventricular myocar-dium (INVM) is a unique cardiomyopathy character-ized by prominent trabeculations and deep intertra-becular recesses in the left ventricle, at times affectingthe right ventricle and interventricular septum as well.In contrast to ‘‘spongy myocardium,’’ INVM occurs inthe absence of other structural heart defects such asright or left ventricular outflow obstruction [Chin et al.,1990]. Previously we showed that patients with thisdisorder develop left ventricular dysfunction, and fre-quently have a clinical course complicated by ventricu-lar arrhythmias and systemic embolization. The patho-genesis of INVM is unknown, but we speculated that it

Steven B. Bleyl and Brian R. Mumford contributed equally tothis work.

*Correspondence to: Thomas K. Chin, M.D., Associate Profes-sor and Chief, Division of Cardiology, Department of Pediatrics,East Tennessee State University, P.O. Box 70578, Johnson City,TN 37614-0578.

Received 8 July 1996; Accepted 9 May 1997

American Journal of Medical Genetics 72:257–265 (1997)

© 1997 Wiley-Liss, Inc.

results from an arrest of normal myocardial develop-ment. Subsequent studies have shown that the preva-lence of INVM is 0.05% of all adult patients examinedwith transthoracic echocardiography [Ritter et al.,1997].

We present a family in whom 6 individuals hadINVM as an X-linked recessive trait. The hearts ob-tained from 4 relatives who died or underwent trans-plantation were evaluated using light and electron mi-croscopy. To determine if fetal echocardiography is use-ful in the prenatal diagnosis of INVM, and todetermine if INVM results from an arrest of normalmyocardial development, echocardiograms were ob-tained between 24–30 weeks of gestation in 3 relativeswho subsequently developed INVM.

Genetic linkage analysis has localized this disorderto the Xq28 region (Bleyl et al., manuscript in press),where three other myopathic disorders with cardiac in-volvement have been mapped. Clinical findings in ourpatients overlap with those found in Barth syndromeand those found in myotubular myopathy, but the mor-phologic changes of INVM appear to be unique. Wepresent the clinical and pathologic findings of this fam-ily and discuss the similarities and differences that ex-ist between our patients and the patients with othermyopathies in this region of the X chromosome.

CASE REPORTS

Figure 1 illustrates the pedigree of this family. Theclinical and pathological characteristics of the affectedpatients are summarized in Table I.

Individuals II-2 and II-3 died in a drowning accidentduring childhood. Individual II-4 died soon after birth;the cause of death was reported as ‘‘sclerema.’’ Indi-vidual III-13 died at age 7 days with sepsis and renalfailure. Individual III-15 was stillborn and had a nu-chal cord. Individuals I-1, II-5, II-9, and III-16 repre-sent obligate female carriers. All are asymptomatic.Only II-5 has had formal cardiac assessment, demon-strating normal physical and echocardiographic find-ings.

Case III-2

The propositus was born after an uncomplicatedterm gestation and delivery. Birth weight was 3,360 g(50th centile), length was 48.5 cm (10th centile), andhead circumference (OFC) was 34 cm (25th centile).Soon after birth the infant developed cyanosis with aninitial capillary pO2 of 28 Torr, pH of 7.24, and O2saturation of 45% on room air. A chest roentgenogramshowed marked cardiomegaly. The infant was trans-ported to a children’s hospital at age 16 hr in congestiveheart failure. On admission the infant became cyanoticwith agitation, heart rate was 170 beats/min, and res-pirations were 50 per/min. Blood pressure was 66/44Torr in the right arm, and equal in all four limbs. Car-diac examination showed a hyperdynamic precordiumwith an apical impulse. No murmurs were heard, butthere was an S3 gallop. The neurologic status was nor-mal, with good muscle tone. An electrocardiogram dem-onstrated right atrial enlargement and S-T segment

depression in precordial leads V1-V2. An echocardio-gram documented ventricular thickening and abnor-mally prominent trabeculations at the left ventricularapex. Ventricular function was depressed, with a frac-tional shortening of 7% (normal, ù30%). The infantwas treated with digitalis and furosemide. Heart ratedecreased to 90–100 beats/min, and ventricular func-tion normalized on hospital day 2. Fever and neutro-penia were present on hospital day 4, and antibiotictherapy was initiated, but blood, spinal fluid, and urinecultures were sterile. The infant was discharged at age10 days in stable condition, but died suddenly at age 21days during a crying episode.

At autopsy, the heart weighed 45 g (expected meanfor age, 23 g [Shulz and Giordano, 1962]), and the rightand left ventricular walls were thick (0.7 and 1.2 cm,respectively; expected means, 0.3 and 0.5 cm). The tri-cuspid and mitral valves were moderately dilated (4.2-and 4.5-cm circumference, respectively; expectedmeans, 3.8 and 3.2 cm), but the pulmonary and aorticvalves were of normal size (2.4 and 2.1 cm, respec-tively). Gross examination disclosed coarse trabecula-tions in both ventricles with extensive endocardial fi-broelastosis, and histologic changes similar to thoseseen in other cases (Fig. 2A). Patchy areas in the sub-epicardial or midmyocardial regions of both ventriclesshowed loosely organized, wavy to angulated fibersthat were thinner than normal, with a reduced contentof myofibrils and central cytoplasmic clearing (Fig. 2D).Periodic acid-Schiff staining of formalin-fixed tissueuncovered increased glycogen in subendocardial cells,but the clear areas in cells in other areas did not stain.The coronary vessels were unremarkable. The tissuesubmitted for electron microscopy was suboptimallypreserved, but showed mitochondria of normal size andshape. Organizing thrombi were noted in both ven-tricles, and emboli of similar age were present in somepulmonary arterioles. There were no hypertensivechanges in the pulmonary arterioles, abnormal periph-eral extensions of smooth muscle along vessels in thedistal lung, or abnormalities of the pulmonary veins orlymphatics.

Case III-5

This younger brother of the propositus (Fig. 3) wasthe product of an uncomplicated term pregnancy anddelivery. His birth weight was 2,951 g (25th centile),and he was described as being ‘‘floppy’’ by his mother.At age 5 weeks, he became limp and unresponsive aftera choking and gasping episode. In the emergency room,vital signs and oxygen saturations were normal inroom air, and his weight was 3,590 g (10th centile). Hewas pale but normally perfused. His lungs were clear,there were no murmurs, and pulses in all four limbswere equal. A chest roentgenogram showed moderatecardiomegaly with a globular silhouette, normal pul-monary flow, and clear lung fields. An electrocardio-gram showed a sinus rhythm, left atrial enlargement,and left ventricular hypertrophy. An echocardiogramdemonstrated left atrial enlargement, and a dilated,hypertrophied left ventricle with extensive trabecula-tions most prominent at the ventricular apex, diagnos-

258 Bleyl et al.

tic of INVM (Fig. 4). Left ventricular function was de-pressed, with a fractional shortening of 12%. He wastreated with digitalis, furosemide, and captopril, andleft ventricular fractional shortening improved to 22%4 days later. A holter monitor recording was normal.The white blood count was 4.7 × 103/mm3, and the ab-solute neutrophil count was 94/mm3. Urinalysis wasnormal, including ferric chloride, dinitrophenhydra-zine for keto acids, nitroprusside for cystine and homo-cystine, nitrosonaphthol for tyrosine, acid albumin andalcian blue for mucopolysaccharides, and amino acidand organic acid chromatography. Serum amino-acidlevels and plasma total and free carnitine levels werewithin normal limits.

The infant was stable until age 8 months when hewas taken to the emergency room in ventricular fibril-lation. He was intubated and converted to sinusrhythm with electrical cardioversion. His weight was5,110 g (<5th centile) and OFC was 43 cm (<5th cen-tile). He was treated with nitroprusside, dopamine,dobutamine, and lidocaine. He experienced one episodeof tachycardia on hospital day 4, but remained in sinusrhythm thereafter. Serial echocardiograms performedon days 1–4 showed an improvement in fractionalshortening from 9% to 20%. Prominent trabeculations

consistent with INVM were again noted in the left ven-tricle, but the right ventricle was normal. Head com-puted tomography and magnetic resonance imagingstudies were normal. Neurologic examination was nor-mal, but indicated delay in psychomotor development.Since the infant was too small for an implantable de-fibrillator, he was listed for cardiac transplantation.

The infant underwent cardiac transplantation at age9 months. The explanted heart weighed 60 g (expectedmean, 42 g), and the left ventricle was dilated withcoarse trabeculation and endocardial fibroelastosis.Histologically, the myocytes showed both hypertrophyand coarse vacuolization with loosely arranged fasci-cles, increased perivascular and interstitial spaces, andperinuclear clearing, though generally less than thatobserved in other cases of INVM. In some sections,moderately increased perinuclear glycogen and mark-edly elongated mitochondria were observed on electronmicrographs. Most mitochondria showed slight varia-tion in shape with rare branching and minimal vesicu-lation of cristae, but no obvious increase in number orsize. Proliferation of cristae, crystalline or amorphousinclusions, or enlarged dense bodies were not seen. Aright deltoid muscle biopsy performed at age 20 monthswas normal histologically and histochemically, and

Fig. 1. Pedigree.

TABLE I. Summary of Clinical and Pathologic Findings*

Clinical findings Case III-2 Case III-5 Case III-19 Case III-21 Case IV-3 Case IV-5

Age at presentation Birth 5 weeks 3.5 months 5 weeks 7 months 6 weeksAge at death 21 days Transplant 3.5 months 5 weeks 7 months Alive at 8 monthsCardiomegaly + + + + + +Cardiac failure/arrhythmias +/ND +/+ +/ND +/+ +/+ +/−Cardiac thrombi + − ND ND − −Neutropenia + + − − − −Muscle weakness − + − − − −Growth retardation ND + + + Premature +Developmental delay ND + ND ND + −Abnormal fetal echocardiogram ND + ND ND − −Pathological findingsHeart weighta 45 g (22 g) 60 g (42 g) ND 59.5 g (22 g) 104 g (40 g) NDDilatation/hypertrophy +/+ +/− +/+ +/+ +/+ NDCoarse trabeculation + + + + + NDEndocardial fibroelastosis + + + + + NDAbnormal myofibers + + + + + NDAbnormal mitochondria − + ND ND − ND

*ND, no data.aThe expected mean [Shulz and Giordano, 1962] is given in parentheses.

Xq28-Linked Cardiomyopathy 259

electron microscopy disclosed normal amounts of lipidand glycogen. Citrate synthase levels were twice thereference range. However, there was fatty replacementof the myofibrils, precluding definitive interpretation.Prospective and retrospective review of a fetal echocar-diogram obtained at 30 weeks of gestation showed mildleft ventricular dilation, but the characteristics ofINVM were not detectable.

A Denver developmental screening test performed atage 34 months showed that fine motor and languageskills were at the 24-month level, while gross motordevelopment was at the 10–11-month level. Weight,height, and OFC were all well below the 5th centile,and physical findings included temporal narrowing,narrow palate, and thin fingers, without other minoranomalies. Reflexes were 1+ bilaterally, with hypoto-nia and joint laxity (Fig. 3).

At last examination (age 54 months), weight andheight remained !5th centile, and motor and cognitivedevelopment was markedly delayed. The patient wasable to dress himself, but lacked the strength to fastenbuttons or snaps. He began crawling at 24 months andwalking at 36 months. He attends preschool, but re-quires physical and speech therapy.

Case III-19

This male infant, a maternal half-cousin once re-moved from the propositus, was the product of an un-complicated term pregnancy. Birth weight was 3,716 g(75th centile). He was the first born of twins. His dizy-gotic brother weighed 3,940 g (90th centile). He washospitalized at age 31

2months for tachypnea, listless-

ness, fever, and anorexia. On admission he weighedonly 4,338 g (<5th centile). His respiratory rate was80/min, he had a regular pulse of 160/min, and four-limb blood pressures were normal. Rales were presentover the left chest to auscultation, the heart was en-larged to percussion, and no murmurs were heard.Both radial and femoral pulses were weak. The liverwas palpable 3 cm below the right costal margin. Onchest roentgenogram, the heart was enlarged but therewas no pulmonary congestion. The electrocardiogramshowed left ventricular hypertrophy. Laboratory dataincluded hematocrit 34%, red blood cell count 4.3 ×106/mm3, white blood count 12.2 × 103/mm3 with 23%segmented forms, 69% lymphocytes, and 8% mono-cytes. The infant died during transport to a tertiarycare center.

Fig. 2. Histologic findings. A: Case III-2. Left ventricle showed deep intertrabecular sinusoids and prominent endocardial fibroelastosis with a rareadherent thrombus (arrow). Masson trichrome, original magnification ×10. B and C: Case IV-3. Sections from opposite sides of the ventricular septumshow a much greater degree of endocardial fibroelastosis on the left (B) than on the right (C). Hematoxylin and eosin, original magnification ×10. D: CaseIII-19. In transverse section (top), myocardial cells show prominent central clearing, while in longitudinal section (bottom) they are narrow and somewhatangulated, with a loss of filaments and perinuclear clear zones internally, and surrounded by an expanded intercellular space. Hematoxylin and eosin,original magnification ×100.

260 Bleyl et al.

A limited autopsy was performed, and histologicslides were available for review. No abnormalities werenoted in the lungs, liver, kidneys, or adrenal glands.Sections of the heart showed prominent trabeculations

with moderate to marked endocardial fibroelastosis,and loosely organized fascicles in subepicardial andmidmyocardial zones composed of thin pale fibers withprominent central clearing (Fig. 2D).

Case III-21

This male infant, a younger brother of case III-19,was the product of a normal full-term pregnancy. Birthweight was 3,248 g (50th centile). Initially, psychomo-tor development was normal. At 5 weeks he was hos-pitalized with listlessness, anorexia, tachypnea, andpallor. Fine rales were noted in the posterior lungbases, the heart was enlarged to percussion, and therewere no murmurs. A chest roentgenogram showed amassively enlarged, globular-shaped heart, and elec-trocardiogram demonstrated biventricular hypertro-phy. Results of complete blood count and urinalysiswere normal. Blood gases were normal on room air.The infant was started on digitalis, furosemide, 40%oxygen by hood, and antibiotics. Despite these mea-sures his condition deteriorated and he died after de-veloping ventricular fibrillation.

Autopsy showed an enlarged heart weighing 59.5 g(expected mean, 22 g), with biventricular hypertrophyand left ventricular endocardial fibroelastosis. Histo-logic study showed prominent trabeculations, looselyarranged fascicles with increased perivascular and in-terstitial space, reduced intracellular filaments, andprominent central clear areas. Infarction or ischemiclesions were not seen. Gross and histologic examina-tion of the lungs, spleen, pancreas, and kidneys werenormal. The liver was slightly enlarged, but histologi-cally normal. The thymus was small, and showed con-siderable involution, but was developmentally normal.Lymph nodes were also depleted, and there was pseu-dotubular change in the provisional adrenal cortex.

Fig. 3. Photograph of case III-5 postcardiac transplantation at age 34months.

Fig. 4. Echocardiography at time of presentation (case III-5). A: Apical four-chamber view demonstrating characteristic prominent trabeculations(large arrow), and deep intertrabecular recesses (small arrows) in the apex of the left ventricle (LV). B: Parasternal long-axis view on echocardiogram fromthe same patient, showing characteristic features of INVM.

Xq28-Linked Cardiomyopathy 261

Case IV-3

This infant, the nephew of cases III-19 and III-21,was born prematurely at 36 weeks of gestation weigh-ing 1,984 g (<10th centile). Prenatal (28 weeks) andearly postnatal echocardiograms were normal. At 7months the infant was admitted to the hospital in car-diogenic shock. For 1 month prior to admission the in-fant was noted to have cold limbs and became diapho-retic with feedings. Weight and length were <5th cen-tile. A chest roentgenogram showed an enlargedcardiac silhouette. Oxygen saturation was 77%. Theelectrocardiogram showed a ventricular ‘‘strain’’ pat-tern. The white blood count was 3.7 × 103/mm3 (abso-lute neutrophil count, 666/mm3). An echocardiogramdemonstrated severe ventricular dilation with mild mi-tral valve regurgitation, and a large pericardial effu-sion. The infant was taken to the operating room,where 75 ml of serosanguinous fluid were recoveredthrough a pericardial window. Viral and bacterial cul-tures of the pericardial fluid were negative. Results ofserum and urine amino-acid screens and plasma-freecarnitine were normal. CMV (IgG) and toxoplasma(IgM, IgG) studies were nonreactive. Karyotype was46XY. On hospital day 3, the infant underwent cardiaccatheterization anticipating cardiac transplantation.During the procedure, the infant died from intractableventricular arrhythmias.

On autopsy, the infant was 56 cm in length (50thcentile for 3 months) with a markedly enlarged heartweighing 104 g (expected mean weight for age, 40 g)with left ventricular hypertrophy (free wall, 1.4 cm;expected mean, 0.6–0.7 cm), coarse trabeculations, andendocardial fibroelastosis. Histologic study showedmarked endocardial fibroelastosis in the left ventricle,but only mild patchy changes in the right ventricle(Fig. 2b,c). Loosely organized fascicles with increasedperivascular and interstitial spaces were seen in thesubepicardial zone of the right ventricle, and in boththe subepicardial and midmyocardial zones of the leftventicle. Myocardial cells in these areas were thin andempty-appearing as a result of decreased fibrils andcentral clearing. Subendocardial cells were coarselyvacuolated. No such lesions were seen in skeletalmuscle of the gastrointestinal (GI) tract. The left lungand liver were moderately enlarged, the former show-ing septal edema and the latter, centrilobular conges-tion and moderately coarse vacuolization. The thymusshowed involution, but normal development. Gross andmicroscopic findings in lungs, kidney, spleen, thyroid,adrenal glands, GI tract, testis, pituitary gland, andbrain were normal. Electron microscopy performed oncardiac muscle showed swollen mitochondria with dis-torted cristae but no elongated forms. Glycogen storeswere normal.

Case IV-5

This infant is the brother of case IV-3. He was bornat term with a birth weight of 2,500 g and length of 48cm (50th and 10th centiles, respectively), following anuncomplicated pregnancy and delivery. A fetal echocar-diogram performed at 24 weeks of gestation (Fig. 5)was normal. The abnormally prominent ventricular

trabeculations and deep intertrabecular recesses seenpostnatally on echocardiograms in patients with INVMwere not apparent. However, with localization of INVMto the Xq28 region by linkage analysis, prospectiveevaluation of this infant using DNA markers predictedthe diagnosis of INVM.

The infant was hospitalized at age 6 weeks with Re-spiratory Syncytial Virus pneumonia. At that time,clinical examination showed congestive heart failure. Achest roentgenogram showed cardiomegaly, and anechocardiogram demonstrated the trabeculations andintertrabecular recesses diagnostic of INVM, depressedleft ventricular function (fractional shortening, 19%),and mitral insufficiency. In the past 6 months, the in-fant has improved on digitalis, lasix, and captopril. Heremains at or below the 5th centiles for age for heightand weight, and has evidence of persistent ventriculardysfunction on echocardiogram, but has had no evi-dence of ventricular arrhythmias or intracardiacthrombi.

DISCUSSIONIsolated Ventricular Noncompaction

We initially described the echocardiographic charac-teristics of isolated noncompaction of the ventricularmyocardium in 8 subjects aged 11 months to 22.5 years[Chin et al., 1990]. Diagnosis was based on the charac-teristic findings of numerous prominent trabeculationsand deep intertrabecular recesses predominantly af-fecting the left ventricular myocardium in the absenceof other strucurual cardiac anomalies. The recesses

Fig. 5. Representative four-chamber view from a fetal echocardiogramperformed at 24 weeks of gestation on case IV-5. The abnormally promi-nent ventricular trabeculations and deep intertrabecular recesses seen onechocardiograms at age 6 weeks in this patient with INVM were not ap-parent prenatally.

262 Bleyl et al.

were lined by endothelium with subjacent zones of fi-brous and elastic tissue. Patients also had associatedsystolic ventricular dysfunction, arrhythmias, minoranomalies, and systemic emboli. Familial recurrencewas noted in 4 males, i.e., 2 brothers and 2 maternalhalf-brothers. Ritter et al. [1997] presented prelimi-nary data reviewing 37,555 transthoracic Doppler-echocardiograms performed over a 9-year period. Sev-enteen subjects met the criteria for INVM (14 malesand 3 females). A familial cardiomyopathy was presentin 2 subjects (father and daughter).

Isolated noncompaction of the ventricular myocar-dium is a rare disorder which may represent a primaryarrest in endomyocardial morphogenesis during theembryonic period. In early embryos, the heart is a looseinterwoven meshwork of muscle fibers. The developingmyocardium gradually condenses, and the large spaceswithin the trabecular meshwork flatten or disappear.INVM appears to be a distinct entity which differs from‘‘spongy myocardium’’ as described in association withcongenital obstructive lesions, which cause pressureoverload of the ventricle [Jenni et al., 1986; Dusek etal., 1975].

Westwood et al. [1975] included a photograph of aheart with endocardial fibroelastosis in which there isprominent trabeculation of the myocardium. This maywell represent an earlier report of ventricular noncom-paction. Similarly, Steiner et al. [1996] may have de-scribed a patient with INVM. In our pedigree, INVMwas seen in all 4 affected patients in whom echocardi-ography was performed, and we conclude that the au-topsy findings in the other 2 infants are consistent withthat diagnosis. Because the isolated form of noncom-paction was described only recently [Chin et al., 1990],previous cases of X-linked INVM may not have beenrecognized. The consistency of morphologic findings inour patients makes this an important additional find-ing in X-linked cardiomyopathy.

Mitochondrial Abnormalities

Mitochondrial abnormalities were an inconsistentfinding in this family. In case III-5, mitochondria fromthe freshly explanted heart appeared in some sectionsto have a bizarre, serpentine appearance. These mito-chondria resembled those shown by Sheldon et al.[1976] in their study on fetal cardiac cells from lambson day 90 of gestation, further supporting the idea thatINVM may arise from an arrest in myocardial devel-opment. However, in case III-5 the cristae were stackedbut not proliferated. Furthermore, postmortem ultra-structural study of the heart in cases III-2 and IV-3showed considerable artifact, but neither the pleoco-nial features described in earlier reports nor the elon-gated forms seen in case III-5. Repeat electron micros-copy performed on frozen cardiac tissue from case III-5failed to show the same bizarre pleomorphism in mito-chondrial shape seen on the earlier study done at timeof transplantation. There may be several explanationsfor this, including the time elapsed between obtainingthe sample and fixation for electron microscopy, anddifferent metabolic states of the mitochondria. In addi-tion, the mitochondrial abnormalities in INVM may be

regional. DiMauro et al. [1985] suggested that definingmitochondrial myopathies by morphological criteria isinappropriate for several reasons. Morphological ab-normalities do not adequately distinguish between dif-ferent mitochondrial myopathies. In fact, multiple mi-tochondrial changes are often seen together in differentproportions within the same individual. Morphologicalchanges in mitochondria are not restricted to syn-dromes resulting from primary errors in mitochondrialfunction, and some patients with defined errors in mi-tochondrial metabolism lack mitochondrial abnormali-ties.

Prenatal Diagnosis of INVM

To determine if fetal echocardiography is useful inprenatal diagnosis of INVM, and to determine if INVMresults from an arrest of normal myocardial develop-ment, echocardiograms were obtained between 24–30weeks of gestation in 3 members of the family whosubsequently developed INVM. The left ventricle wasdilated in one fetal heart, but the studies were other-wise of no use in the prenatal diagnosis of INVM. Theabnormally prominent ventricular trabeculations anddeep intertrabecular recesses seen postnatally on echo-cardiograms in patients with INVM were not apparentprenatally. These findings suggest that fetal echocar-diography is not reliable for prenatal diagnosis ofINVM, and that the echocardiographic changes associ-ated with INVM either develop postnatally (implyingthat INVM does not result from developmental arrestof the myocardium), or are not visible on fetal echocar-diograms using the available technology. While fetalechocardiography may be useful when ventricular dys-function is present, it does not appear to be diagnosticfor INVM.

In contrast, evaluation of case IV-5 with DNA mark-ers from the Xq28 region predicted the diagnosis ofINVM in a family member who subsequently presentedwith INVM. It appears that DNA testing will allowprenatal diagnosis of INVM.

Xq28 Region Myopathies

Cardiomyopathies which cluster in the Xq28 regioninclude Emery-Dreifuss muscular dystrophy (EDMD),myotubular myopathy (MTM), and Barth syndrome.

Emery-Dreifuss muscular dystrophy (MIM 310300)is characterized by slowly progressing muscle contrac-tures, which tend to precede a humeroperoneal muscleweakness and wasting. Neurological abnormalities areusually absent, and onset tends to occur in late child-hood [Consalez et al., 1991; Yates et al., 1993]. Cardio-myopathy is manifested by conduction defects, withatrial standstill and heart block invaribly occurring bythe third decade of life. Atrophy of cardiac muscle cellsand extensive myocardial fibrosis are also seen. Re-cently a mutation in the STA gene (Xq28) which codesfor a serine-rich protein called ‘‘emerin’’ was describedin a study of 5 cases [Bione et al., 1994].

Myotubular myopathy (MIM 31040) was first de-scribed by Spiro et al. [1966] and is thought to repre-sent an arrest or delay in myocyte maturation. Musclefibers in this disorder show the characteristic fetal

Xq28-Linked Cardiomyopathy 263

morphology of myotubes with central nuclei, perinucle-ar halos, and myofibril deficit. Congestive heart fail-ure, aortic stenosis, ventricular hypertrophy, and ar-rhythmias have been described in this disorder. Neu-rological manifestations include ptosis, strabismus,hyporeflexia, ophthalmoplegia, and seizures. Musclefindings include extraocular, facial, and neck muscleweakness and congenital eventration of the dia-phragm. Secondary respiratory complications are com-mon and include respiratory distress and aspirationpneumonia. Other findings include a long thin face, ahigh-arched palate, weak cry, undescended testes, cav-ernous hemangioma of the liver, thoracolumbar defor-mities, and maternal polyhydramnios. Although onsetoccurs in childhood or adolescence in most cases, deathin utero or early infancy is not uncommon [Raju et al.,1977; Darnfors et al., 1990; Liechti-Gallati et al., 1991].This disorder may be inherited in autosomal-recessive,-dominant, and X-linked recessive forms, but the neo-natal X-linked form is the most common and severevariant [Keppen et al., 1987; Fidzianska et al., 1994].The gene for X-linked myotubular myopathy was iso-lated recently [Laporte et al., 1996].

Barth et al. [1983] characterized an X-linked reces-sive condition (Barth syndrome) in a Dutch family as-sociated with the triad of dilated cardiomyopathy, neu-tropenia, and skeletal myopathy (MIM 302060). Ultra-structural abnormalities were observed in neutrophils(myelocytic arrest), in cardiac muscle cells, and to alesser extent in skeletal myocytes (mitochondrial ab-normalities). Additional findings included early onsetwith death in infancy or early childhood, growth retar-dation, borderline plasma carnitine deficiency, lowmuscle carnitine, intermittent lactic acidemia, respira-tory chain abnormalities, and endocardial fibroelasto-sis. Significant neurological findings are usually ab-sent. Later, other investigators added to the spectrumof associated findings by reporting instances of el-evated urinary organic acids and myopathic facies [Inoet al., 1988; Kelley et al., 1991; Ades et al., 1993;Christodoulou et al., 1994]. Bolhuis et al. [1991] firstlocalized the genetic defect in Barth syndrome by link-age analysis to the Xq28 region. Ades et al. [1993] re-fined this localization as being distal to DXS374.Gedeon et al. [1995] presented a family in which sev-eral male infants died of a hypertrophic cardiomyopa-thy without short stature, skeletal myopathy, and neu-tropenia. A family history of unexplained male infantdeaths spanning four generations was also present. Ge-netic linkage analysis localized the disorder to theXq28 region distal to DXS296. Recently, mutations inthe G4.5 gene were found to cause Barth syndrome infour families [Bione et al., 1996]. The function of theG4.5 gene protein products, called taffazins, is un-known.

The affected patients we present here share somemanifestations with the other myopathies in the Xq28region summarized above. Consistent findings in oursubjects are those of endocardial fibroelastosis, cardiacdilation, or hypertrophy with prominent trabeculaeproducing the echocardiographic findings of isolatednoncompaction of the left ventricular myocardium, andloosely arranged fascicles of myocytes, especially in the

subepicardial regions and more prominent in the leftventricle. Ultrastructural abnormalities of the mito-chondria were inconsistently expressed.

ACKNOWLEDGMENTS

The authors thank the members of XLCM kindred1736 for their cooperation with this study. Thanks alsogo to Dr. Jan Byrne for providing clinical information,and to Dr. Julie Brown and Dr. Craig Zuppan for pro-viding information on pathology and electron micros-copy.

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