Disease-causing Gene Mapping And Candidate Gene Analysis Of Single Gene Disorders

A novel locus for autosomal dominant hereditary gingivalfibromatosis, GINGF3, maps to chromosome 2p23.3-p22.3Gingival fibromatosis (GINGF, MIM135300) is a rare, benign disorder characterizedby slowly progressive fibrous overgrowth of maxillary and mandibular keratinizedgingiva. It occurs mainly at the stage of permanent teeth eruption, however, caseshave also been reported to appear during the deciduous dentition or even after birth.The phenotypic spectrum is considerably broad and variable, both in distribution(number of teeth involved) and in degree (severity of expression). It is known thatboth genetic and pharmacological factors can cause such kind of gingival enlargement.Although sporadic cases and syndromic form could be seen in clinic and autosomalrecessive inheritance has been reported, hereditary gingival fibromatosis (HGF) isusually non-syndromic and transmitted with autosomal dominant pattern. It is recentlyreported that autosomal dominant HGF transmission can be affected by genomic DNAmethylation. Before our research, two loci have been mapped in familial cases withautosomal dominant non-syndromic HGF: GINGF (MIM135300) on chromosome2p22-p21, GINGF2 (MIM605544) on chromosome 5q13-q22, only SOS1 (son ofsevenless one, MIM182530) gene underlying GINGF locus has been identified asdisease cause gene. In this study, we ascertained a large Chinese five-generation HGFfamily through proband confirmation. Exclusion analysis showed that the diseaselocus was mapped on 2p, which is the early reported GINGF locus region. We directlysequenced all exons, exon/intron boundaries and flanking regulating region of SOS1gene, but no mutation was found. Then we performed fine mapping and constructedhaplotype with more STS markers on short arm of chromosome 2. The recombinationevent on haplotype of this pedigree localized the locus to an 11.4-cM interval betweenmarkers D2S2221 (telomeric) and D2S1788 (centromeric). The maximum two-pointlimit of detection (LOD) score of 3.45 (θ=0) and multipoint LOD score of 5.00 formarker D2S390 strongly supported linkage to this region. Thus, this genetic interval is distal to and does not overlap with the previously described locus, GINGF, on2p21-p22. This novel HGF locus has been nominated GINGF3 by HUGOnomenclature committee. More recently study shows that there's another novel HGFlocus on chromosome 11p15, which is affected by maternal imprinting status. But nodisease-cause gene has been identified under this locus. Candidate Gene Screeningof Non-Syndromic Postaxial Polydactyly PAPA3 locusLimb malformations are frequently seen in newborn abnormalities. Both geneticand environmental factors can induce limb malformation. Of genetic factors,monogenic mutations, multifactorial diseases and chromosome aberrations areincluded. Postaxial polydactyly (PAP; MIM174200) is one of the most commonlyseen limb malformations. Within the reported familial postaxial polydactyly cases,gene mutations on chromosome 7, 13 and 19 can cause PAP phenotype. There're twotypes of postaxial polydactyly phenotype: of type A, the extra digit or toe is ratherwell formed; of type B, the extra digit or toe is not well formed and is frequently inthe form of a skin tag without bone structure. Radhakrishna et al. mapped the firstPAPA1 locus to chromosome 7p15-q11.23 in 1997. Then they found a GLI3 genemutation on codon 764, which was identified as PAP disease-cause mutation. At thesame year, Akarsu et al. mapped the second PAPA2 locus on chromosome 13q21-32.In 2002, Zhao et al. of our department mapped the third PAPA3 locus on chromosome19p13.2-13.3. And the next year, Galjaard et al mapped another PAPA4 locus onchromosome 7q22.Within the 2.68 Mb genome interval of PAPA3 locus, there are 95 known geneslocated, of which 65 are function known and 31 are unknown. In our study, we havescreened 21 genes by Polymerase Chain Reaction-sequencing method, but nodisease-associated nucleotide change was found. Of these 21 genes, we had finishedsequencing all exons and exon-intron boundaries of 16 genes. As the other 5 genes,few exons were left unfinished. In this study, we found three novel genomic sequencevariations that are not listed in dbSNP. One is C＞T change at the 35th base on exon11of EMR2 gene, which causes the codon change from GCC to GTC and amino acidalternation from Alanine to Valine. Another is G＞A alternation of-9 position on intron12 of the same gene EMR2. The third one is 22bp duplication on the 3' side of intron5 of RFX1 gene. Through pedigree co-segregation analysis and population allelefrequency analysis, these three nucleotide variations were identified as novelpolymorphisms but not disease-cause mutation. We will try to find more clues throughfunctional candidate strategy, select more prior candidate genes, and finally to find outthe disease-cause gene underling the PAPA3 locus.