Molecular Genetic Analysis Of Achondroplasia And Congenital Cataract In Families

This thesis includes two sections on two independent, but related, genetic projects. The first project is mutational analysis of the FGFR3 gene in a Chinese family with autosomal dominant achondroplasia. The second project is on mapping of the disease-causing gene in a large Chinese family with autosomal dominant congenital cataract (ADCC) by a genome-wide linkage scan.(1) Achondroplasia (ACH) is the most common form of autosomal-dominant skeletal disorders and caused by recurrent missense mutations in the fibroblast growth factor receptor 3 gene (FGFR3). More than 98% of ACH cases are casued by a single G380R mutation in the transmembrane receptor domain. However, other FGFR3 mutations associated with ACH have also been reported. We characterized a Chinese family with ACH. Blood samples were collected from the family members and genomic DNA was isolated. Direct DNA sequence analysis of all exons and exon-intron bandraries of FGFR3 was carried out, and a pathogenic mutation was identified and further confirmed by restriction fragment length polymorphism (RFLP) analysis. The mutation is a novel missense mutation that results in a single heterozygous A to T transversion at nucleotide 649, and substitution of the highly conserved Ser217 residue in the second immunoglobulin (Ig)-like domain of FGFR3 by a cysteine residue. RFLP analysis showed that the Ser217Cys mutation co-segregated with all affected individuals in the family, but was not present in unaffected family members and 200 normal controls. These results show that the Ser217Cys mutation in FGFR3 is responsible for ACH in the Chinese family, and represents the first mutation identified in the Ig II domain of FGFR3 associated with ACH.(2) Congenital cataract is a severe lens-related disesae that causes blindness. It is mainly cuased by metabolic malfunction of lens during the embryonic development period and the resulting declined transparency of lens. It is one of the major causes of blindness in humans, and shows high, clinical and genetical heterogeneity. We characterized a large four-generation Chinese family with congenital cataract, in which 22 family members were used for genome-wide linkage analysis. Haplotype, two-point LOD and multi-point LOD analysis have been performed to define the disease gene interval. The cataract locus in the family was mapped to chromosome 20p12.1-p11.23 with the maximum two-point LOD score of 5.15 for marker D20S471 (θ=0), and the gene was found to be within a 7.54 Mb (12.49 cM) interval between markers D20S915 and D20S912. Sequence analysis of the BFSP1 gene at the locus did not reveal any mutation. These results provide a framework for future identification of a new cataract gene at the chromosome 20p locus.