Identification Of X-linked Congenital Generalized Hair Histiocytosis Pathogenic Mutation

Congenital generalized hypertrichosis (CGH) has generate much scientific interest and media attention largely due to the striking hairy phenotype and its apparently atavistic nature. The CGH is a genetically and phenotypically heterogeneous group of rare conditions characterized by universal hair overgrowth. It is the major phenotypic feature of many distinct genetic syndromes and can be inherited as an autosomal or X-linked dominant trait.To date, genetic defects have been found in two forms of autosomal dominant CGH. Autosomal dominant congenital generalized hypertrichosis terminalis with or without gingival hyperplasia (MIM 135400) is associated with copy number variations (CNVs) on chromosome 17q24. Rearrangements of chromosome 8 and a possible position effect have been detected in hypertrichosis universalis congenita, Ambras type (MIM 145701). X-linked congenital generalized hypertrichosis (MIM 307150), an extremely rare condition characterized by universal overgrowth of terminal hair, was first mapped to chromosome Xq24-q27.1 in a Mexican family. However, the underlying genetic defect remains unknown.We had ascertained a five-generation Chinese family with a new syndrome combining CGH, scoliosis and spina bifida. The family had 11 affected individuals. All four affected males had severe hypertrichosis associated with scoliosis while all affected females had only mild hypertrichosis which was consistent with X-linked inheritance. We mapped the disease locus to a 5.6-Mb critical region within the interval defined by the previously reported Mexican family during the initial research period.To determine whether the new X-linked CGH syndrome was caused by an unknown microdeletion or microduplication, we performed a genome-wide high-resolution CNV scan in four affected individuals using the Affymetrix Genome-Wide Human SNP Array 6.0. We did not detect potential pathogenic CNVs in the critical region but found a> 121-kb microduplication of the COL23A1 locus on 5q35.3 in all the four individuals. The following qPCR assay confirm the microduplication and also showed full segregation of the microduplication with the disease phenotype in the family. Moreover, the genotyping of microsatellite markers from the 5q35.3 region excluded a linkage to this region. We performed two-color interphase and metaphase fluorescence in situ hybridization (FISH) and confirmed an insertion of the duplicated region to somewhere between Xq26.3 and Xq28. In parallel with the above-described CNV and FISH analyses, we conducted targeted capture and massively parallel sequencing (MPS) in the proband using the Roche NimbleGen SeqCap and 454 Sequencing technologies, and used genome-walking strategy to amplify the insertion junctions. We identified the interchromosomal insertion at Xq27.1 of a 125,577-bp intragenic fragment of COL23A1 on 5q35.3, with one X breakpoint within and the other very close to a human-specific short palindromic sequence located 82-kb downstream of SOX3.In the reported X-linked CGH Mexican family, examination of four family members for CNVs with the SNP Array 6.0 revealed a microduplication of a>278-kb fragment on 4q31, encompassing PRMT10 and TMEM184C and involving parts of ARHGAP10 and EDNRA, in affected members. The microduplication was validated by a qPCR assay. Using a similar junction PCR approach, we ascertained an interchromosomal insertion at the same Xq27.1 site of a 300,036-bp genomic fragment on 4q31.2, with both the two X breakpoints within the short palindrome.The two palindrome-mediated insertions were confirmed to fully segregate with the CGH phenotype in each of the families, and the CNV gains of the respective autosomal genomic segments are not present in the public database. Analysis of control individuals revealed deletions ranging from 173-bp to 9,104-bp at the site of the insertions with no phenotypic consequence. Taken together, our results strongly support the pathogenicity of the identified insertions and establish X-linked congenital hypertrichosis syndrome as a genomic disorder.