Genetic Mapping In A Chinese Family With Autosomal Dominant Congenital Cataract

ObjectiveCongenital cataract is a common blindness threatening disease among children. The epidemiology survey disclose that the prevalence ratio is (0.6～6)/10000 and the neonate incidence is (2.2～2.49)/10000.1/3 of the cataract are hereditary cataract. Hereditary cataract includes autosomal dominant congenital cataract (ADCC), autosomal recessive congenital cataract and X-linked congenital cataract. ADCC is the most common type. Patients brings heavy burdens to both family and society. Following by the development of the Genetics and Molecular Biology,we foud that at least 22 genes are related to congenital cataract at present, including 10 crystallin protein genes (CRYAA,CRYAB,CRYBB1,CRYBB2,CRYBB3,CRYBA4,CRYBA1/A3,CRYGC,CRYGD,CRYGS);4 membrane protein genes which contains gap junction protein genes (GJA3,GJA8),main interior membrane protein genes (M7P26)and lens interior membrane protein (LIMI/MP19); transcribe accommodate factors (MAF, PITX3, HSF4, PAX6);cytoskeletal protein gene2 (BFSP2);ephrin A receptor gene (EPHA2);chromatin modify protein gene (CHMP4B) and ferroprotein gene (FTL). This is a populational country which is rich of hereditary resources. To find out novel causative genes and to better understand their mechanism is our goal to benefits human being and prenatal investigation and inquiry. ADCC is gene defect, which is being workout in molecular level. The outcomes of the research work in this field will fully support the hereditary interference and genomic therapy theoretically. The present study introduces a Liaozhong area of Northeasten resident family with hereditary cataract. A series of research work had been done in screening and identifying the novel gene mutation.Materials and Methods We collected family materials and gave them physical examination to exclude their general diseases and other ocular abnormalities. Pupil had been dilatated and anterior segment photographies had been documented. Phenotypes of proband had been identified clinically and pedigrees had been drawn carefully. After signed the informed consent, peripheral blood samples (4 ml per individual) were collected from the proband and family members including non-affected members,and storaged in-70℃refrigerator. Genomic DNA was extracted from their whole blood using Universal Genomic DNA extraction kit Ver.3.0. A total 52 polymorphic microsatellite markers at chromosome 1p36,1q21-q25；2q33-q35,3q21-q25,10q25,11p13. 11q23-q24,12q12-q14,13q11-q13,16q22,16q23,17q11-q12,21q22.3122q11-q12 were selected and genotyped for linkage analysis. Sequence information for PCR primers were obtained from the NCBI website. Primers were commercially synthesized. All family members were subject to PCR genotyping. The PCR fragments were separated through 8% denaturing polyacrylamide gel electrophoresis. Two-point linkage analysis between the cataract phenotype and genetic markers were performed using the MLINK component of the LINKAGE package. Haplotype was constructed using allele information of this family.To calculate LOD score:LOD≥3,the two-point linkage exists.LOD≤-2,fail to linkage.LOD score between-2 and 3, indicates linkage relation.According to the allele and the relation between family member artificially construct the family haplotype.For the ascertained domain in the chromatosome, gene sequencing is needed to identify the mutation.ResultsA total of 21 individuals,including 8 patients (2 males and 6 females),And 15 individuals were available for examination.Blood samples were collected from 15 individuals,including 8 patients.The pattern of phenotype transmission in this families suggested a mode of autosomal dominant inheritance.Microsatellite polymorphic markers were successfully genotyped by polyacrylamide gel electrophoresis and silver staining. Two-point linkage analysis did not provide evidence for linkage to markers from chromosome regions 1p36,1q21-q25,2q33-q35,3q21-q25,10q25,11p13,11q23-q24,12q12-14,13q11-q13,16q22.1,16q23,21q22.3,22q11-q12. However, a maximum LOD score of 2.71 were obtained at chromatosome 17q11-12 for marker D17S469 and D17S184 (θ=0),suggested that pathogenic gene is in this chromatosome domain.ConclusionThe result of the linkage analysis indicated the pathogenic gene located in chromatosome 17q11-q12. The pathogenic mutation is not the mutation of the exons and untranslated region in CRYBA1/A3. The study could not exclude other gene mutation or mechanism lead the morbility of this autosomal dominant congenital cataract. Futher certificated that ADCC families exist hereditary heterogeneity.