Journal ofMedical Genetics, 1984, 21, 173-177

Homozygosity for autosomal dominant MarfansyndromeJUAN CHEMKE*, RACHEL NISANI*, AMI FEIGLt, RIVKA GARTYt,MICHAEL COOPER', YEHUDIT BARASH+, AND DAN DUKSIN§

From the *Clinical Genetics Unit, tHeart Institute, and 4Department ofPediatrics B, Kaplan Hospital(affiliated to the Hebrew University and Hadassah School of Medicine); and §Department ofBiophysics, Weizmann Institute of Science, Rehovot, Israel.

SUMMARY Marfan syndrome is an autosomal dominant condition with varying phenotypicmanifestations. Affected persons are usually heterozygotes. A family is presented in which the genefor this syndrome is segregating in a large number of members. Two sibs suffered from unusuallysevere, identical, and fatal manifestations from birth, their parents having mild cardiovascularand somatic symptoms common in Marfan syndrome. Investigation of collagen biosynthesis infibroblasts revealed no abnormalities in fibronectin and procollagen I and III synthesis andsecretion or in the procollagen to collagen conversion. We suggest that these two sibs are examplesof homozygosity for the Marfan syndrome gene, based on the large number of affected members,the absence of additional consanguinity, manifestation of the syndrome in both parents, and theseverity of the disease in the two sibs.

Marfan syndrome is one of the more frequentautosomal syndromes. Its frequency has beenestimated at 4 to 6 in 100 000 births. Approximately15% of the cases are spontaneous mutations.1 Thereis great variability of the phenotypic manifestationsof the disease which may be explained in part byvariable penetrance of the gene or genetic hetero-geneity.2 As in most autosomal dominant diseases,affected subjects are usually heterozygous for themutant gene.We report a family in which the gene for Marfan

syndrome is segregating. In this kindred, a largenumber of persons have different manifestations ofthe disease. Two sibs are described in detail, withidentical uncommonly severe manifestations frombirth. These patients raise the possibility of homo-zygosity for the Marfan syndrome gene. Thepossibility of an autosomal recessive 'Marfan-like'disease of connective tissue cannot be definitelyruled out at present, since so far no specific abnormalcollagen for Marfan syndrome is known.

Family history and case reports

The family pedigree is presented in fig 1. The familyis of Jewish-Yemenite origin. The parents (111.3 andReceived for publication 19 April 1983.Accepted for publication 7 October 1983.

111.4) of the proband (IV.1) and his sister (IV.2) arefirst cousins. They are tall compared with othermembers of the family and considering their ethnicorigin. Their only skeletal manifestation of Marfansyndrome is a moderately excavated sternum. Theyboth have elinical and echocardiographic evidenceof cardiovascular disease: mitral prolapse andaortic ectasia (I1.3) and mitral prolapse only(I1.4) (fig 2). Ophthalmological examination wasnormal. The pedigree also shows that a large numberof family members have at least two major mani-festations of Marfan syndrome, such as arachno-dactyly, cbest deformities, scoliosis with loosejoints, and aortic insufficiency or a floppy mitralvalve or both.The two sibs (IV.1 and IV.2) had progressively

severe manifestations from birth and died in earlyinfancy. Their pertinent physical findings aresummarised in the table. The older child (fig 3) wasborn after 38 weeks' gestation with a birth weight of3250 g. Head circumference was 36 cm. At birth, anunusual phenotype was noted. The face was elong-ated, with antimongoloid slanting eyes and cornealopacities. The palate was high and narrow. Theforehead was narrow and hairy. The anteriorfontanelle was very large and there was a widemetopic suture. The skin and joints were loose andarachnodactyly of the hands and feet was evident.

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A right inguinal hernia was found. With age, joint feet. Ocular findings consisted of subluxation of thelaxity, arachnodactyly, dorsal kyphosis, and pectus lens, megalocornea, and blue sclerae. At the age ofexcavatum became prominent. There was a tendency 3 months, a holosystolic murmur grade 3/6 wasto dislocation of the small joints of the hands and first heard at the cardiac apex and radiated to the

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FIG 2 M-mode echocardiography of the patients' parents. (a) III.3, left ventricle and mitral valve. Arrow: prolapse ofposterior mitral leaflet. (b) III.3, left ventricular outflow tract and aortic valve region. Arrows: enlarged aortic root.

(c) III.4, left ventricle and mitral valve region. Arrows: slight prolapse of the posterior valve region.

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Homozygosity for autosomal dominant Marfan syndrome

TABLE Pertinent physicalfindings in patients IV.Iand IV.2.

At birthSkin Loose, not elasticJoints Dislocations, hypermobility of fingers,

contracture of hips and elbowsSkeletal Arachnodactyly, camptodactyly, chest deformityHernias Inguinal, umbilical

Early infancyCardiac Severe and progressive mitral regurgitation,

progressive cardiac and coronary insufficiencyPulmonary Emphysema, spastic bronchitis, recurrent

pulmonary infectionsOcular Ectopia lentis, megalocornea

FIG 4 Selective left ventriculography ofproband.Small arrows: enlarged left ventricle (L V) and ectasiaof aortic sinuses (AS). Large arrows: huge left atrium(LA) owing to mitral regurgitation.

FIG 3 General appearance of the proband. Note facialfeatures, loose skin, arachnodactyly, joint contractures,and chest deformity.

axilla. Cardiological evaluations revealed progressivemitral insufficiency with prolapse of the mitralleaflets. Chest radiographs showed cardiomegaly(fig 4). Repeated echocardiography showed progres-sive dilation of the aortic root, and systolic flutterand pansystolic prolapse of both mitral leaflets(fig 5). He suffered from recurrent respiratoryinfections and progressive cardiac insufficiency. At15 months of age cardiac catheterisation confirmedthe presence of severe antral dilation and severedilation of the aortic sinuses. He developed chestpains and electrocardiographic evidence of antero-lateral myocardial infarction. He died at 2- yearsof age at the time of open heart surgery for mitralvalve replacement. Mental development was normal.

Pathological examination showed dissection of thepulmonary artery above the pulmonary sinuses.There was severe mucoid degeneration of the mitraland tricuspid valves and a thin and partially dis-organised elastic network.The clinical course and findings in the younger

sib were practically identical. She was born after anuneventful term pregnancy weighing 3080 g. Birthlength was 51 - 5 cm and head circumference 36-5 cm.She had very long limbs, a high palate, arachno-dactyly, marked pectus excavatum, and joint andskin laxity. A holosystolic murmur was noted frombirth. Echocardiography showed prolapsed mitralleaflets. Radiographs showed a markedly enlargedleft ventricle. The lenses were dislocated. Shedeveloped progressive cardiac failure from 6 monthsof age and recurrent respiratory tract infectionswith spastic components. Cardiac catheterisation atthe age of 2 years revealed severe mitral insufficiencywith prolapse of the mitral valve and aortic ectasiawith dilation of the aortic root. She too died at21 years of age of cardiac failure. No necropsy couldbe performed.Numerous laboratory tests, including amino-acid

chromatography and cytogenetic studies, revealedno abnormalities, excluding those related to theacute phases of the disease at its different stages.Collagen biosynthesis was studied on fibroblastsgrown in tissue culture from a skin biopsy obtainedfrom the proband, with the use of radioactive

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proline and mannose, protein precipitation bytrichloroacetic acid,3 slab gel electrophoresis, andfluorescent autoradiography.4 The total quantity ofcollagenous proteins was determined in the mediumfraction after dialysis against distilled water andlyophilisation.3 The collagen content of the growthmedium from the proband's fibroblasts was 322%compared to an average of 3 0% in medium fromtwo age and sex matched control fibroblast cultures.The patterns of fibronectin and procollagens types Iand III from the fibroblast culture medium of theproband were very similar to those of controlcultures, as well as the extracellular enzymaticconversion of procollagen type I. No furtherinvestigations were possible for technical reasons.

Discussion

Marfan syndrome is an autosomal dominant diseasein which a defect in the biosynthesis of collagen isprobably involved, or a structural alteration in someother category of connective tissue.1 5 As in otherautosomal dominant traits, variable expressivity ofthe gene results in a wide range of clinical manifes-tations, possibly as a consequence of variable genepenetrance and genetic heterogeneity. Therefore, theactual prevalence of Marfan syndrome is unknownand may be much greater than the estimated 4 to 6in 100 000. Affected subjects are usually hetero-zygotes for the mutant gene.2

14omozygosity for autosomal dominant traits isrelatively rare in human genetics, and its phenotypicexpression is frequently much more severe thanthat of the heterozygous state. Examples ofsuch cases include achondroplasia, the moderate

FIG 5 M-mode echocardiographyofproband. (a) Enlarged leftventricle (open arrows, LV),fluttering ofposterior (P) mitralleaflet owing to ruptured chordaetendineae, and mitral valveprolapse (arrow). (b) Leftventricle (LV) with multipleechoes (arrows) within mitral valveproducing a 'tumour-like'appearance owing to redundantmitral valve. (c) Enlarged aorticroot (open arrows, AO).

type of autosomal dominant brachydactyly, thePelger-Huet anomaly of leucocytes, hereditaryhaemorrhagic telangiectasia, and familial hyper-cholesterolinaemia.6One of the difficulties in characterising Marfan

syndrome is the absence of a specific demonstrabledefect in the biosynthesis of collagen. Lysyl oxidaseactivity, the enzyme that initiates cross linking, hasbeen reported to be normal in fibroblasts. Thecollagen in skin fibroblasts of affected subjects ismore easily extracted in aqueous and denaturatingbuffers than collagen in normal controls.8 14ow-ever, the stability of the insoluble fraction isdecreased only in growing adolescent patients.10Furthermore, skin fibroblasts from patients withMarfan syndrome synthesise approximately fivetimes more hyaluronic acid than normal human skinfibroblasts." It has been suggested that this isbecause of a defect in the control of the synthesis ofhyaluronic acid'2 owing to increased activity of thehyaluronic acid synthetase.'3 Several alterations inthe biosynthesis of collagenous proteins in patientswith Marfan syndrome have been described. Theseinclude differences in the proportions of collagentypes I and III14 and changes in the ultrastructureand composition of collagen in aortic tissue.15 In thelatter case, the aortic tissue contained two distinctac2 chains of collagen type I. Reduced amounts ofchemically stable forms of intermolecular cross linksin skin fibroblasts were recently observed,'6 and itwas suggested that the cause of this defectivecollagen could be in altered maturation. It has beenproposed that these cross link abnormalities aresecondary to a primary gene defect in the oc2(I)peptide.'7 Dermal fibroblasts from a patient with

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H0omozygosity for autosomal dominant Marfan syndrome

Marfan syndrome were shown to synthesise two x2collagen chains of which one contained an insertionof approximately 20 amino-acids.17 The oc2(I) genes

have been assigned to chromosome 7 by molecularhybridisation.5 Biochemical analyses of a largenumber of Marfan syndrome patients are necessary

in order to determine whether the appearance of an

abnormal o2 collagen chain is a general and specificdefect in this condition.We propose that the two severely affected sibs

represent examples of homozygosity for the Marfangene. This assumption is based on the severe andsimilar course of the Marfan-like disease and thepresence of Marfan syndrome in both parents in a

family in which a large number of persons have thissyndrome. Homozygosity for Marfan syndrome mayhave occurred in a large family described in1959 and mentioned by McKusick, in which thereweie some subjects much more severely affectedborn to first cousin parents.18However, other possible genetic mechanisms have

to be considered, even though none can be provenowing to the lack of a specific detectable abnormalityof collagen. Fried and Krakowski19 postulatedautosomal recessive inheritance for Marfansyndrome in a family in which there were twoaffected sisters in a sibship with completely normaland non-consanguineous parents. In the familypresented here, the parents are first cousins and bothpatients had a similar disease. Therefore, it could beassumed that the patients are homozygous for anautosomal recessive gene. The parents would thus beheterozygous and mildly affected.Another genetic model could be the presence of

double dominant heterozygosity in both patients.Each parent would be heterozygous for an auto-somal dominant gene for a different type ofabnormalcollagen at different loci, and their offspring wouldthus be heterozygotes for each one of these genes.Mutations at different loci, with alterations ofdifferent subunits of collagen, are potentiallypossible, even though they have not been demon-strated so far.

Until further knowledge is obtained on a specificmolecular defect in Marfan syndrome, geneticcounselling will be based on theoretical recurrencerisk figures. Assuming that the two patients re-present homozygosity for the autosomal dominantMarfan syndrome gene, the recurrence risks in eachpregnancy would be 25% and 50% for homozygousand heterozygous Marfan syndrome, respectively.

This work was supported in part by a grant from theAdvancement of Mankind foundation (to DD).

References1Pyeritz RE, McKusick VA. The Marfan syndrome:diagnosis and management. N Engl J Med 1979;300:772-7.

2 Pyeritz RE, Murphy EA, McKusick VA. Clinicalvariability in the Marfan syndrome(s). Birth Defects1979;XV(5B):155-78.

3Duksin D, Bornstein P. Impaired conversion of pro-collagen to collagen by fibroblasts and bone treated withtunicamycin, an inhibitor of protein glycosylation.JBiol Chem 1977;252:955-62.

4Duksin D, Mahoney WC. Relationship of the structureand biological activity of the natural homologues oftunicamycin. J Biol Chem 1982;257:3105-9.

5Pyeritz RE, McKusick VA. Basic defects in the Marfansyndrome. N EnglJ Med 1981 ;305:1011-2.

6 Vogel F, Motulsky AG. Human genetics. Problems andapproaches. New York: Springer-Verlag, 1979.

7 Layman DL, Narayanan AS, Martin GR. The produc-tion of lysyl oxidase by human fibroblasts in cultUre.Arch Biochem Biophys 1972;149:97-101.

8 Laitinen 0, Uitto J, Livanainen M, Hannuksela M,Kivirikko KI. Collagen metabolism in Marfan'ssyndrome. Clin Chim Acta 1968;21:321-6.

9Priest RE, Moinuddin JF, Priest JH. Collagen in Marfansyndrome is abnormally soluble. Nature 1973 ;245:264-6.

10 Francis MJO, Sanderson MC, Smith R. Skin collagen inidiopathic adolescent scoliosis and Marfan's syndrome.Clin Sci Mol Med 1976;51 :467-74.

1 Matalon R, Dorfman A. The accumulation of hyaluronicacid in cultured fibroblasts of the Marfan syndrome.Biochem Biophys Res Commun 1968 ;32:150-4.

12 Lamberg SI, Dorfman A. Synthesis and degradation ofhyaluronic acid in the cultured fibroblasts of Marfan'ssyndrome. J Clin Invest 1973 ;52:2428-33.

13 Appel A, Horwitz AL, Dorfman A. Cell-free synthesis ofhyaluronic acid in Marfan syndrome. J Biol Chem 1979;254:12199-203.

14 Halbritter R, Aumailley M, Rackwitz R, Kreig T,Muller PK. Case report and study of collagen metabolismin Marfan's syndrome. Klin Wochenschr 1981 ;59:83-90.

15 Scheck M, Siegal RC, Parker J, Chang YH, Fu JCC.Aortic aneurism in Marfan's syndrome: changes in theultrastructure and composition of collagen. J Anat 1979;129:645-57.

16 Boucek RJ, Noble NL, Gunja-Smith Z, Butler WT. TheMarfan syndrome: a deficiency in chemically stablecollagen cross-links. N EnglJ Med 1981 ;305:988-91.

17 Byers PH, Siegal RC, Peterson KE, et al. Marfan syn-drome: abnormal a2 chain in type I collagen. Proc Nat!Acad Sci USA 1981;78:7745-9.

18 McKusick VA. Heritable disorders of connective tissue.St Louis: Mosby, 1972.

19 Fried K, Krakowsky D. Probable autosomal recessiveMarfan syndrome. J Med Genet 1977;14:359-61.

Correspondence and requests for reprints to DrJuan Chemke, Clinical Genetics Unit, KaplanHospital, 76 100 Rehovot, Israel.

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