Characterisation of X;17(q12;p13) translocation breakpoints in a female patient with hypomelanosis of Ito and choroid plexus papilloma.

An X;17 translocation breakpoint was characterised in a 5-year-old female with hypomelanosis of Ito (HI) who exhibits characteristic hypopigmented lesions, psychomotor retardation, and choroid plexus papilloma. A YAC clone containing the locus DXS1 from Xq12 was found by fluorescence in situ hybridisation to cross the translocation breakpoint. Cosmid clones positive for DXS1 were used to identify and clone the translocation junction fragment from the patient's DNA. A chromosome-17-specific DNA fragment was isolated and used to identify cosmid clones crossing the translocation from chromosome 17p13. Exon trapping identified two known genes from chromosome 17: FMR1L2 (the fragile X mental retardation syndrome like protein 2) and SHBG (human sex hormone-binding globulin). Mapping the FMR1L2 and SHBG genes showed that neither gene was disrupted by the translocation.