Refined Localization Of Dyschromatosis Symmetri Hereditaria Gene To A 9.4-cM Region At Lq21-q22 And Mutation Detection Of ADAR Gene

Background Dyschromatosis symmetrica hereditaria (DSH, 0MIM#127400) is an autosomal dominant pigmentary genodermatosis characterized by hyperpigmented and hypopigmented macules of on the extremities. The disorder appears in infancy or early childhood and the skin lesions commonly stop spreading before adolescence and last for life. It predominantly occurs in Asian. Our group performed a genome-wide search in two large Chinese families with DSH and firstly mapped the chromosome location to an 11.6-cM region at Iq11-q21. To facilitate the identification of DSH gene we performed refined mapping of DSH locus. When we are on the way to clone the DSH gene, Miyamura et al. identified the RNA-Specific Adenosine Deaminase Gene (ADAR, OMIM#601059) responsible for DSH among Japanese families recently. Therefore we directly performed mutation detection of the ADAR gene in 6 Chinese families and 2 sporadic cases with DSH by sequencing.Objective (1) to refine the previously mapped region that facilitates the identification of DSH gene (2) to identify the spectrum of mutations in ADAR and verify if genotype-phenotype correlations could be established (3) to delineate the clinical and genetic features of Chinese DSH cases by a literature review of 136 cases reported in ChinaMethod (1) All available individuals from two multi-generation families were genotyped with 14 polymorphic microsatellite markers from Iq11-q21. Two-point linkage analysis was performed with Linkage programs version 5.10. Haplotypes wereconstructed with Cyrillic Version 2.02 software. (2) We designed primers flanking all 15 coding exons and intron-exon boundaries of the ADAR gene using the web-based version of the Primer 3.0 program, then sequence the ADAR gene in 6 Chinese Families and 2 Sporadic Patients with DSH. (3) We searched for case reports and papers about DSH since 1980 by Chinese Biology Medicine (CBM) disc and PubMed. The genetic and clinical features of DSH in China were summarized.Results: (1) A cumulative maximum two-point lod score of 3.68 was produced with marker D1S506 at a recombination frequency of 9=0.00 in two DSH families. Haplotype analysis refined DSH locus to a 9.4-cM interval flanked by D1S2343 and D1S2635. LOD scores greater than 3 were also observed at the neighboring markers D1S2715, D1S2777 and DlS303.(2)Haplotype analysis refined DSH locus to a 9.4-cM interval flanked by D1S2343 and D1S2635. (3)Seven novel heterozygous mutations of ADAR were identified in 6 Chinese Families and 2 Sporadic Patients WITH DSH, which were c.2433₂434delAG (T811fs-841X), c.2197G>T (E733X), C.3286OT (R1096X), c.2897G>T (C966F), C.2797OT (Q933X), c.2375delT (L792fs-792X) and c.3203-2A>G (IVS12-2A>G) respectively. The c.2433₂434delAG (p.T811fs) mutation was found in all patients but not in the healthy individuals from Family 1. The c.2375delT (p.L792fs) was found in sporadic patient 1 but not in his healthy parents and a healthy sister. These two mutations lead to frameshift and premature translation termination within exon 7. The truncated proteins with no functional activity would be synthesized from the gene with these two frameshift mutations. The c.2197G>T (p.E733X) mutation was identified in the Family 2. The predicted protein lacks 494 amid acids, including part of the double-stranded RNA binding motif (DSRM) and tRNA-specific and double-stranded RNA adenosine deaminase (ADEAMc) domains. The c.3286C>T (p.R1096X) was carried by all patients from both Family 3 and Family 4. The predicted protein lacks 131 amid acids, which are part of the ADEAMc domain.The c.2797C>T (p.Q933X) mutation in Family 6 is also located in the putative deaminase domain and the predicted protein lacks 294 amid acids. The missense c.2897G>T (p.C966F) mutation in exon 11 was found in Family 5. This mutation replaces a highly conserved cysteine residue with phenylalanine. The amino acid residue at 966 in exon 11 is located in the putative deaminase domain. This mutation was not detected in the 100 unrelated, population-match control ind...