Occupational and Environmental Medicine 1996;53:439-444

Mutation rates at the glycophorin A and HPRTloci in uranium miners exposed to radon progeny

E M Shanahan, D Peterson, D Roxby, J Quintana, A A Morley, A Woodward

AbstractObjectives-To find whether a relationexists between estimated levels of expo-sure to radon and its progeny and muta-tions in hypoxanthine phosphoribosyltransferase (HPRT) and glycophorin A ina cohort offormer uranium miners.Methods-A cohort study involving asample of miners from the Radium Hilluranium mine in South Australia, whichoperated from 1952 to 1961. Radiationexposures underground at Radium Hillwere estimated from historical radon gasmeasures with a job exposure matrix.Workers from the mine who workedexclusively above ground according tomine records were selected as controls. In1991-2 miners were interviewed and bloodtaken for measurement of somatic muta-tions. Mutation rates for HPRT and gly-cophorin A were estimated with standardassay techniques.Results-Homozygous mutations of gly-cophorin A were increased in under-ground miners (P = 0.0027) and themutation rate tended to rise with increas-ing exposure with the exception of thehighest exposure (> 10 working levelmonths). However, there was no associa-tion between place of work and either thehemizygous mutations of glycophorin Aor the HPRT mutation.Conclusions-There may be an associa-tion between glycophorin A mutationsand previous occupational exposure toionising radiation. However, not enoughis known at present to use these assays asbiomarkers for historical exposure inunderground mining cohorts.

(Occup Environ Med 1996;53:439-444)

Keywords: uranium miners; glycophorin A; HPRT;radon progeny

There is currently great interest in the role ofsomatic mutations as potential biomarkers forradiation exposure. Identification of biomark-ers may lead to: (a) more valid and preciseclassification of exposure to radiation inhumans; (b) a better understanding of radia-tion effects on incidence of disease at lowdoses (thereby allowing for more accuratestandard setting); (c) better screening tools forearly carcinogenic or precarcinogenic effects,with the potential for earlier intervention andimproved health outcomes in early carcino-

genic cases, or prevention strategies in precar-cinogenic cases; (d) improved understandingof the process of carcinogenesis in humans.'

According to some authors, the combina-tion of central effects and precision of mea-surement make genetically based radiationdosimetry a unique tool for cancer preven-tion.2 Others suggest that exposures to envi-ronmental mutagens are unlikely to besufficiently large to allow interpretation ofmutation rates in individual men to be mean-ingful. They argue that the main role of theseassays will be to facilitate the study of the bio-logical process of mutagenesis and carcinogen-esis.3 All agree that the assays require furtherstudy in a variety of populations.Two of the most promising mutation assays

seem to be the hypoxanthine phosphoribosyl-transferase (HPRT) assay and the glycophorinA (GPA) assay. The HPRT assay identifiesmutations at the X linked HPRT locus on thelymphocyte.45 A significant, dose dependentincrease in HPRT mutations was found in agroup of patients who received local irradia-tion for tumour treatment6 and also in a groupof men environmentally exposed to radon.7A study of atomic bomb survivors assayed 43years after exposure showed a small but signif-icant increase in HPRT mutation rates.8 9The GPA assay measures mutation rates of

the genes coding for the M or N blood groupantigens on the surface of red cells.Glycophorin A is the main glycoprotein foundin the red cell membrane. In the presence ofcertain mutagens, the gene code responsiblefor the production of glycophorin can mutatewith no selection disadvantage to the red cellproduced. The mutations are of two types,hemizygous (NO) and homozygous (NN).Like the HPRT assay the GPA assay has beenused in atomic bomb survivors to analysemutation rates.'O l1 These studies show a dosedependent increase in mutations 40 years afterexposure, which is strong evidence that themutational lesions are stably integrated intostem cells. In Chernobyl workers a similardose response was seen.'2 To our knowledge,there have been no previous reports of HPRTor GPA mutations in underground minerswhose environmental exposure to ionisingradiation is due principally to the short liveda emitting decay products of radon (radonprogeny).

Materials and methodsSTUDY POPULATIONThe Radium Hill mine was an underground

Department ofMedicine, FlindersMedical Centre,Bedford Park SA 5042,AustraliaE M ShanahanD RoxbyJ QuintanaA A MorleyDepartment ofHaematology, TheQueen ElizabethHospital, WoodvilleRd, Woodville SA 5011,AustraliaD PetersonWellington School ofMedicine, Universityof Otago, WellingtonSouth, New Zealandand formerly ofDepartment ofCommunity Medicine,University ofAdelaide,Adelaide 5000,AustraliaA WoodwardCorrespondence to:Dr E M Shanahan,Department of Medicine,Flinders Medical Centre,Bedford Park SA 5042,Australia.Accepted 21 February 1996

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uranium mine in the mid-north of SouthAustralia which supplied ore to the UnitedStates Atomic Energy Commission and theUnited Kingdom Government between 1954and 1961. Pay records held by the SouthAustralian Department of Mines indicate that2574 workers were employed over the life ofthe mine.13 The mine used the standard venti-lation techniques available for undergroundmines at the time and as a consequence, com-pared with most modern underground mines,its workers were exposed to relatively high lev-els of radon and its progeny (mean (range)exposure 8 (0-122) working level months(WLM)). Follow up of these workers to theend of 1987 showed that lung cancer deathrates were higher than expected comparedwith national mortality rates, and within thecohort lung cancer mortality increased withcumulative exposure to radon progeny.13A sample of the workers who participated in

the mortality follow up study were invited totake part in the current study and a total of253 men agreed. The men in this sample wereselected principally because of their proximityto the laboratory (it was necessary that theywere living in metropolitan Adelaide), as theassays required relatively rapid processingafter venesection. Also the subjects needed tobe fit enough to respond to questions concern-ing their occupational and medical histories,and willing to donate venous blood for theproject. In all, 92% of those contacted agreedto participate in the study. Reasons given for afailure to participate included too difficult (1),too old to participate (1), demented (2),unwilling to give blood (3), not there longenough (1), unwilling but no reason given (7),and refusal by a relative (2).

QUESTIONNAIREA questionnaire was given by trained inter-viewers to gather information on variableswhich were considered to be possible con-founders of the relation between radiationexposure and somatic mutation rates. The fac-tors considered included age, cigarette smok-ing, other radiation exposures, exposure toother potential mutagens, medical history,alcohol history, and hobbies. Sex was not con-sidered as all subjects were men.

EXPOSURE ESTIMATESRadiation exposure estimates were calculatedby converting measurements of concentrationsof radon to radon decay products with infor-mation available on mine ventilation. In all721 measurements of radon concentrationwere made in the mine between 1954 and1961. At the start of mining, there was onlynatural ventilation (estimated at 2 m'/s) whichwas boosted to 5 m3/s in mid-1954 with theinstallation of a Venturi fan. In March 1955, amain fan was installed, increasing the ventila-tion to about 45 m3/s. For the period January1954 to March 1955 the radon monitoringresults were averaged for each level of themine. A mean air residence time was calcu-lated from the mine void and ventilation rate.This was used to calculate the equilibrium fac-

tor to convert concentration of radon to con-centration of radon-I 1 decay product. Thusconcentrations of radon decay product wereestimated for each level of the mine.

After the main fan was installed, there weresufficient radon monitoring results to allow anestimate of the radon concentrations in threeregions of the mine (drives, stopes, and thearea of the main shaft), as well as the meanconcentration on each level. A mine ventila-tion model was developed with information oncontemporary practices and recollections ofthe workers from the mine. The ages of air indrives and stopes of other levels were esti-mated by interpolation, and concentrations ofradon decay product were estimated withequilibrium factors derived as above. Theresult of these calculations was a matrix show-ing for each year, the estimated concentrationsof radon decay products for each level and forstopes, drives, and main shaft regions on eachlevel.

Exposures of miners were estimated in thefollowing way. For each of the job categorieslisted in the employment records, an estimatewas made of the proportion of time that wouldbe spent in each of the three regions (shaft,drive, stope). Mining plans were then exam-ined to find in which years appreciable miningwas undertaken on each level. An estimate wasmade of the proportion of time that each cate-gory of worker would spend on each level ineach region. These proportions were multi-plied by the estimated concentrations of radondecay product for that level and region. Thesum of these products gave the mean concen-trations of radon decay product to which thatjob category was exposed in that year. Eachindividual worker's exposure was computedfrom the employment record. The duration ofemployment in each job category was calcu-lated and then multiplied by the appropriateconcentration of radon decay product fromthe exposure matrix. Zero exposure wasassigned to all surface work. Cumulative expo-sures then were computed by adding themen's exposures throughout their employmentperiod. Also, verbal estimates of time workedunderground by the men themselves were col-lected as an alternative estimate of exposure.

After the interview, 20 ml of venous bloodwas taken from the cubital fossa of each partic-ipant by a standard technique including atourniquet. The blood samples were labelled,placed in an insulated container (kept at roomtemperature), and transferred immediately forprocessing. To test for variation within eachman and to test assay reliability 34 participantshad their tests repeated on a separate occa-sion.

LABORATORY METHODSGlycophorin A assayDetection of variant erythrocytes was per-formed with the previously published BR6glycophorin A assay of Langlois et al. 14 The redcells were sphered immediately and wereanalysed the next day. Fluorescently labelledmonoclonal antibodies were used to see the Mand N antigens of the MN blood group. The

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3

2

a-cr0-Z 1

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Under Aboveground ground

Figure 1 HPRTmutation rates in

underground and aboveground workers.

o

HPRTAssayThe HPRT assay was performed on peripheralblood lymphocytes as described previously byMorley et al.'7 The method is based on theability of mutated lymphocytes, which aredeficient in HPRT, to be able to proliferate inthe presence of thioguanine.

I

I

Undergroundtotal

Abovegroundtotal

I

UndergroundNNAbovegroundNN

UndergroundNO

AbovegroundNO

Figure 2 GPA mutation rates in underground and aboveground workers.

number of NO and NN mutants in MN menwas assessed with a flow cytometer. The mon-oclonal antibodies used in the assay have beendescribed previously.'5 16 Flow cytometricanalysis of the labelled samples was performedon a FACScan single laser flow cytometer withthe consort-30 software analysis package(Becton Dickinson Immunocytometry Sys-tems, Mountain View, California).

Table 1 Mean (95% CI) mutation rates in underground and above ground workers atRadium Hill

Log GPA Log GPA Log GPALogHPRT (total) (NN) (NO)mutation rate mutation rate mutation rate mutation rate

Above ground workers 1-29 (n = 88) 1-39 (n = 46) 0-93 (n = 46) 1-13 (n = 46)(1-21 to 1-36) (1-28 to 1-49) (0-79 to 1-06) (1-02 to 1-22)

Underground workers 1-23 (n = 134) 1-48 (n = 79) 1-23 (n = 79) 0 911 (n = 79)(1-17 to 1-29) (1-39 to 1 55) (1-13 to 133) (0-83 to 0 98)

P value 0-223 0 11 0-0006 0 0011

Table 2 Mean (95% CI) mutation rates ofHPRT and GPA and exposure to radonprogeny at Radium Hill

Log GPA Log GPA Log GPAExposure Log HPRT (total) (NN) (NO)catagoty mutation rate mutation rate mutation rate mutation rate

<0-1WLM 1-29(n=88) 1-39(n=46) 093(n=46) 1 12(n=46)(1-22 to 1-36) (1-29 to 1-49) (0-79 to 1-06) (1-02 to 1-22)

0 1-5WLM 1-18 (n = 74) 1-41 (n = 46) 1 20 (n = 46) 0O81 (n = 46)(1-10 to 1-26) (1-31 to 1-52) (1-07 to 1-34) (0 71 to 0-91)

5-1-10 WLM 1-34 (n = 27) 1-65 (n = 13) 1 40 (n = 13) 1-15 (n = 13)(1-26 to 1-53) (1-46 to 1-85) (1 14 to 1-65) (0-97 to 1-33)

> 10 WLM 1-20 (n = 33) 1-50 (n = 20) 1 19 (n = 20) 0O98 (n = 20)(1-08 to 1-33) (1-33 to 1 65) (0-98 to 1.39) (0-83 to 1-12)

P value, test forlinear trend 0-74 0-16 0-08 0-94

STATISTICAL ANALYSISThe GPA results were reported as the numberof variant cells per million red blood cells. TheHPRT assay results were reported as a muta-tion frequency-that is, the number of clon-able cells in the presence of thioguaninedivided by the number of clonable cells in theabsence of thioguanine. The assay results werelogarithmically transformed before applicationof statistical analyses. Associations betweenmutation rates and estimated radiation expo-sures were investigated by analysis of variance.Orthogonal polynomial contrasts were used totest for a linear trend. The possibility of simplenon-linear models fitting the data was exam-ined, but none did. Adjustments were madefor potential confounders with linear regres-sion and analysis of covariance. The possibilityof examining radon exposure as a continuousvariable was examined, but this approach wasnot informative.

Statistical analyses were performed with theSAS/STAT software.'8 The linear regressionanalyses of the repeat blood samples were per-formed with the Instat (GraphPAD software)program.

ResultsWe first examined the relation between themutation rates in those workers exposed toradon (underground workers) versus those notexposed (above ground workers). Under-ground workers included all who workedunderground for some of their time at RadiumHill. Above ground workers included menwho only worked on the surface for their timeat Radium Hill.

Figure 1 shows the distribution of the datafor the HPRT assays in underground andabove ground workers. Figure 2 shows the dis-tribution of the glycophorin A assay data.

Table 1 shows the mean (95% confidenceinterval (95% CI)) mutation rates in under-ground and above ground workers at RadiumHill.

Table 2 shows the relation between HPRTand GPA mutation rates and cumulative expo-sure to radon progeny at Radium Hill, (mea-sured in WLM).

CONFOUNDING VARIABLESOf the workers 75% were either currentsmokers (37%) or ex-smokers (38%). Themean (SD) cigarette smoking dose (in ciga-rettes/day x years smoked) was 431 (479) forabove ground workers (n = 105) and 516(483) for underground workers (n = 143).The difference between cigarette smokingdoses between the two groups were not signifi-cant (P = 0-17).The mean age of the above ground workers

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Table 3 Estimated mean exposures to various confounders v work underground atRadium Hill and estimated dose stratified by WLAI

x rays toCigarette Time in lumbar CT Nuclear

Mean dose other mines region scans med scansage (pktly) (month) n n n

Worked underground:yes 62-4 515-7 71-8 3-3 0-8 0-2no 63-3 435 36 2 0-5 0-3

Exposure (WLM):<0-1 633 435 36 2 05 030-1-5 62 546-8 59 1 3-3 07 035-1-10 61 7 394-4 105 6 4-2 1-2 0-2> 10 64 558-6 752 2-7 04 0-2

was 63-3 years (n = 105), and that for under-ground workers was 62A4 years (n = 143).

Table 3 shows further information onpotential confounders.Few participants reported other potential

confounders such as other occupational expo-sures to radiation or medical conditionsinvolving radiotherapy or chemotherapy. Oneman had been treated with chemotherapy forcancer, two had received radiotherapy, and 17men stated that they had worked in jobs whichmay have resulted in other radiation exposure.

Multivariate analyses were performed toassess any potential combined contributionfrom confounders including: cigarette smok-ing, age, alcohol use, x ray films, other miningwork, or work where exposure may haveoccurred, medical conditions where exposuremay have occurred, other medical conditions,possible exposure to mutagenic substances innon-occupational environments, history ofblood transfusions, and presence at Maralinga(an atomic bomb testing site).As age and cigarette smoking are thought to

be the most important of these variables, ananalysis controlling for these two variables wasperformed (table 4). There was no significantchange in the relations of the variables versus

Table 4 Mutation rates in above and undergroundworkers, adjustedfor age and cigarette smoking (log meanmutation rates)

Mutation assay Above ground workers Underground workers

HPRTGPA (Tot)GPA (NN)GPA (NO)

1-281-380-921-12

1-23 (P = 0 29)1-47 (P = 0-19)1-23 (P = 0-0006)0-91 (P = 0-18)

Table 5 Mutation rates in above and undergroundworkers, adjustedfor potential confounders using analysisofcovariance (log mean mutation rates)

Mutation assay Above ground workers Underground workers

HPRTGPA (Tot)GPA (NN)GPA (NO)

1-141-461-051-04

1-06 (P = 0-13)1-61 (P= 007)1-39 (P = 0 0027)0-93 (P= 0-18)

Table 6 Comparison data on repeat assays

CorrelationAssay Samples n coefficient P value

HPRT 19 0-29 0-22GPA (Tot) 34 0-93 < 0-0001GPA (NN) 34 0-82 < 0-0001GPA (NO) 34 0-42 0-015

exposure. This is not surprising consideringthe similarities in the two groups in their ageand smoking histories.When the analysis was adjusted for all the

confounding variables the GPA (total) andGPA (NN) mutation frequencies were still sig-nificantly increased in underground workersbut the mean GPA (NO) frequency was notsignificantly different from that for the controlgroup (table 5).

ANALYSIS OF THE REPEATED SAMPLESRepeat assays (34 GPA and 19 HPRT) wereperformed on second blood samples collectedfrom a subsample of 34 participants. Table 6shows the results of the comparison of theseassays. The GPA assays were highly repro-ducible but the HPRT assays were not.

DiscussionThis study shows no clear relation betweenHPRT mutation rates and previous occupa-tional exposure to radon. However there is asignificant relation between mutation rates ofglycophorin A and the estimates of radonexposure. Higher total mutation rates for gly-cophorin A were found in underground work-ers than above ground workers. This pattern isdue chiefly to an increase in NN type muta-tions. There is a tendency for glycophorin Atotal mutations to increase with exposure upto the highest exposure category (>10 WLM).This trend is not significant and is mainly dueto the contribution of the homozygous type.

There is an increase in the homozygousmutation type with increasing dose, with aflattening at the highest exposure category(greater than 10 WLM).Adjustment for an extensive list of possible

confounders did not alter the results in anysubstantial way. It strengthened the evidenceof increased GPA total and NN mutation inunderground workers (table 5) and it alsocaused the NO mutation result to be no longernotably at odds with our hypothesis. This sug-gests that the unexpectedly negative result inthe unadjusted data (table 1) may have at leastin part been due to confounding factors.

There are several strengths in this particularstudy. Firstly, the work is human basedresearch performed on a cohort of workers inthe type of situation where such assays mayfind application in the future. Secondly, unlikemany other studies involving historical expo-sures, detailed estimates of personal exposureswere available. The exposure estimates havepreviously been correlated with increased ratesof lung cancer deaths in this cohort, whichincreases their credibility.'3 A further strengthof the study is the internal control group(above ground workers) which reduces thelikely influence of confounding factors. Themost important of the confounders is age, butother important variables include sex, cigarettesmoking, alcohol history, occupational histo-ries, and medical histories.The assays were all performed at a single

laboratory by staff well trained in theprocesses. The high correlation found in the

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repeat specimens in the glycophorin assays isfurther evidence of the quality of the labora-tory procedure. The repeat HPRT assays didnot show as close a correlation as the gly-cophorin assay, but this would be expectedfrom the statistics of the two assays. A typicalglycophorin assay scores three to 10 moremutational events than a typical HPRT assay,and this factor alone would lead to the coeffi-cient of variation for the HPRT assay being1-7-3-2 times that of the glycophorin assay.The ages of cohort members means there

will be opportunity in the short to mediumterm to relate disease outcome to mutationresults. This work could then contribute toour knowledge of biomarkers of effect. Therelatively low exposure to radon progeny atRadium Hill (compared with other uraniummines of the time) may limit the ability of thestudy to detect increased levels of mutations,but the circumstances of the Radium Hill min-ers relate more directly to modem day expo-sures than most previous cohorts ofunderground miners.The finding that the HPRT assay did not

detect an effect of radiation exposure is anapparent contradiction both to previous find-ings by other workers6-9 and to our presentfindings of an increase in glycophorin NNmutations. Factors in the present study whichmight explain failure to detect an effect are: alow absolute exposure at Radium Hill; a lowdose rate at Radium Hill; and the 30 yearswhich elapsed between exposure and study asthere is evidence that the HPRT mutations areselected against in vivo. 19 Our findings ofHPRT and glycophorin mutations are, in fact,internally consistent rather than contradictory.Glycophorin NN mutations, the type found tobe increased, are thought to result from chro-mosomal mechanisms such as mitotic recom-bination and such mechanisms are notdetectable by the HPRT assay as the HPRTlocus is situated on the X chromosome.Glycophorin NO mutations are thought to bedue to point mutation or deletion, the samemutational mechanisms as detected by theHPRT assay and they were likewise notdetectably increased. There are other possibili-ties. Obviously, there may not have been anassociation in reality or the association mayhave been so small as to be not detectable byour assay.The glycophorin mutations detected in cir-

culating erythrocytes must have reflectedmutational events in the stem cells of the bonemarrow. The mechanism by which the red cellprecursors are irradiated by inhaled radonprogeny is thought to be through absorptioninto the bloodstream.20 Radon and its progenyare relatively fat soluble and absorption intothe fat cells of the marrow is thought to be thepossible explanation for increases reported inrates of myeloid leukaemia in areas of highdomestic radon.21The application of biomarkers in occupa-

tional health practice faces considerable tech-nical, legal, and ethical difficulties. Biomarkersof effect are especially contentious when theoutcome is a malignancy (such as lung cancer)

which responds poorly to treatment. In thesecircumstances the use of somatic mutations in aclinical setting clearly may do more harm thangood unless it is possible to identify a sub-group of affected workers whose cancers areunusually susceptible to treatment. This studysuggests that there may be a relation betweenoccupational exposures to radon progeny andlong lasting increases in some somatic muta-tions. However, our current knowledge is farshort of providing a useful tool for screeningworkforces such as underground miners.Further work in this area will hopefully enlargeunderstanding of the biological effects of ionis-ing radiation and point the way towards betterestimates of the radiation doses received byworkers. The value of this work must be bal-anced against the psychological morbidity thatmay be imposed on people who are told thattheir mutation rates are high.

We thank Dr Phil Crouch from the SA Health Commission forthe calculation of the radiation exposure estimates, KristynWillson for her valuable statistical advice, Marg Lee for under-taking much of the field work, and Tania Siviour for her techni-cal assistance. The SA Mining and Quarrying Fund for partialfunding of this research.

1 Perera F. Molecular cancer epidemiology: a new toolin cancer prevention J Nad Cancer Inst 1987;78:887-98.

2 Mendelsohn ML. New approaches for biological monitor-ing of radiation workers. Health Phys 1990;59:23-8.

3 Morley AA. Human somatic mutations-where are wegoing? In: Mendelsohn M, Albertini RJ, eds. Mutationand the environment part C: somatic and hertiable mutation,adduction, and epidemiology. New York: Wiley-Liss,1990:1-5.

4 Albertini RJ, Castle KL, Borcherding WR. T-cell cloningto detect the mutant 6-thioguanine-resistant lymphocytespresent in human peripheral blood. Proc Nad Acad SciUSA 1982;79:6617-21.

5 Morley AA, Trainor KJ, Seshardri RS, Ryall RG.Measurement of in vivo mutations in human lympho-cytes. Nature 1983;302:155-6.

6 Messing K, Seifert AM, Bardley WEC. In vivo mutant fre-quency of patients exposed to ionizing radiation. 4thInternational Congress on Environmental Mutagenesis.Stockholm: 1985:65.

7 Bridges BA, Cole J, Arlett CF, Green MH, Waugh AP,Beare D, et al. Possible association between mutant fre-quency in peripheral lymphocytes and domestic radonconcentrations. Lancet 1991 ;337: 1187-9.

8 Hakoda M, Akiyama M, Kyoizumi S, Awa A, Yamikido M,Otake M. Increased somatic cell mutant frequency inatomic bomb survivors. Mutat Res 1988;201:38-48.

9 Akiyama M, Kyoizumi L, Hirai Y, Hakoda M, NakamuraN, Awa A. Studies on chromosome aberrations andHPRT mutations in lymphocytes and GPA mutations inerythrocytes of atomic bomb survivors. In: MendelsohnM, Albertini RJ, eds. Mutation and the environment, partC: hertiable mutation, addiction, and epidemiology. NewYork: Wiley Liss, 1990:68-80.

10 Langlois RG, Bigbee WL, Kyoizumi S, Bean M, AkiyamaM, Nakamura N. Jensen R. Evidence for increasedsomatic cell mutation of the glycophorin A locus inatomic bomb survivors. Science 1987;236:445-8.

11 Kyoizumi S. Nakamura N, Hakoda M, Awa AA, Bean MA,Jensen R, Akiayama M. Detection of somatic mutationsat the glycophorin A locus in erythrocytes of atomicbomb survivors using beam flow sorter. Cancer Res 1989;49:581-8.

12 Langlois RG, Bigbee WL, Jensen RH. The glycophorin Aassay for somatic cell mutations in humans. In:Mendelsohn M, Albertini RJ, eds. Mutation and theenvironment part C: somatic and hertiable mutation, adduc-tion, and epidemiology. New York: Wiley-Liss, 1990:47-56.

13 Woodward A, Roder D, McMichael AJ, Crouch P,Mylvaganam A. Radon daughter exposures at theRadium Hill uranium mine and lung cancer rates amongformer workers, 1952-87. Cancer Causes Control 1991;2:213-20.

14 Langlois RG, Nisbet BA, Bigbee WL, Ridinger DN, JensenRH. An improved flow cytometry assay for somaticmutations at the glycophorin A locus in humans.Cytometry 1990;11:513-21.

15 Bigbee WL, Vanderlaan M, Fong SS, Jensen RH.Monoclonal antibodies specific for the M- and N- formsof human glycophorin A. Mol Immunol 1983;20:

1353-62.16 Langlois RG, Bigbee WL, Jensen RH. Flow cytometric

characterization of normal and variant cells with mono-

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clonal antibodies specific for glycophorin. Am Jf Immunol1985;134:4009-17.

17 Morley AA, Trainor, KJ, Dempsey JL, Seshardri RS.Methods for study of mutations and mutagenesis inhuman lymphocytes. Mutat Res 1985;147:363-7.

18 SAS Institute. SASISTAT guide for personal computers, ver-sion 6. Cary, North Carolina: SAS Institute, 1987.

19 Dempsey JL, Morley AA, Seshardri RS, Emmerson B,Gordon R, Bhagat C. Detection of the carrier state for

an X-linked disorder, the Lesch-Nyhan syndrome, bythe use of lymphocyte cloning. Hum Genet 1983;64:288-90.

20 Richardson RB, Eatough JP, Henshaw DL, Dose to redbone marrow from natural radon and thoron exposure.BrJIRadiol 1991;64:608-24.

21 Henshaw DL, Eatough JP, Richardson RB, Radon as acausative factor in induction of myeloid leukaemia andother cancers. Lancet 1990;335:1008-12.

Occupational and Environmental Medicine and theelectronic age

OEM has an Email address which is100632.3615@compuserve.com. We wel-come contact by Email, including letters tothe editor. Some of our reviewers alreadysend us their reports by Email, helping tospeed up the peer review process.We are moving towards electronic pub-

lishing and for some months now we havebeen asking authors to send us their revisedpapers on disk as well as a hard copy. I amdelighted to report that nearly all ourauthors are managing to comply with this

request; far more than for other specialistjournals in the BMJ Publishing group.Oddly enough, the few authors who havenot sent us a disk version of their revisedpapers have been almost exclusively fromthe United Kingdom. I would be interestedin suggestions for why this might be.Perhaps United Kingdom based authorsread our correspondence and instructionsless assiduously? Watch for revisedInstructions to Authors.

The Editor

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