Screening Of Pathogenic Variants In Two Genetic Disease Families

Background:Retinitis pigmentosa(RP)is caused by progressive degeneration of photoreceptor cells that primarily affect the rods whatever the function of the cones is compromised as the disease progresses.The worldwide prevalence of RP is about 1 /3000-1/7000,RP ranks first in single-gene Inherited Retinal Disease.Marfan syndrome(MFS)is an autosomal dominant hereditary and multiple-systemic disease,mainly involving the ocular,skeletal and cardiovascular systems.The incidence of MFS is 1/3000-1/5000,>90% of MFS were caused by FBN1 mutations.The application of Whole Exome Sequencing technology can effectively find out the genes of genetic diseases.Objects and methods: Two Chinese consanguineous autosomal recessive retinitis pigmentosa(ARRP)families(RP-2284 and RP-2360)and five autosomal dominant(ADRP)Marfan sydrome families(Marfan-2342 、 Marfan-2346 、 Marfan-2348 、Marfan-2349 and Marfan-2350)were recruited in this study.All the family members received complete ophthalmic examination,including sight,fundus photography,electroretinography(ERG)and so on.Excepting that,all MFS family members also underwent complete physical,and cardiovascular examination.Whole Exome Sequencing(WES)was performed to screen for pathogenic genes,followed by directly Sanger sequencing.Possible functional changes caused by the mutations were predicted by using bioinformatics program Polyohen-2,SIFT and HOPE.Result: Two novel homozygous missense mutations c.1997 T>A(p.Val 666 Asp)and c.2426A>C(p.Glu809Thr)in the crumbs homolog 1(CRB1)gene which is known to cause severe retinal pigmentosa,were found in RP-2284 and RP-2360,respectively.Three novel heterozygous mutations in FBN1,including c.4987T>G(p.C1663G)、c.5032T>G(p.Tyr1678Asp)and c.1708 T>G(p.Cys570Gly),as well as two known mutations c.718C>T(p.Arg240Cys)and c.2584T>C(p.Cys862Arg)were identified in five MFS families.Each mutation was found to be co-segregated with RP and MFS phenotype in each family and was not found in the unaffected members and 1086 normal controls.Multiple sequence alignment of the human CRB1 and FBN1 protein showed that these mutations occurred in a highly conserved region among different species.SIFT、Polyohen-2 and HOPE predicated that these seven homozygous missense mutations are all damaging.Conclusion: Two CRB1 mutations were identified in two RP families and five FBN1 mutations were identified in Chinese with MFS.These data extends the mutation spectrum of CRB1 and FBN1 genes in Chinese population and provides theoretical basis for genetic counseling and prenatal diagnosis of these two diseases.