Abstract
Mutation of the Hypoxanthinep hosphoribosyltransferase gene (HPRT1) cause Lesch-Nyhan (LN) syndrome, which is characterizedb y hyperuricemia, s elfmutilationa nd behavioradl ysfunctiona, nd approximately 15% of LN mutations involve large deletions and large duplications. In this study, we have identified a novel mechanism of a mutationi nvolvingt ranslocation between the HPRT1 gene and an other gene on the X chromosome. In HRT-25's cDNA obtained from a patient with LN syndrome, the upstream region of exon 3 wasa mplified, b ut thef ull-lengthr egiono f exon3 was not amplified. T he use of 3' rapida mplificationo f cDNA ends polymerase chain reaction (3' RACE-PCR) for mRNA from HRT-25 demonstrated a part of intron 3and an unknown sequence starting at the 3' end of exon 3. Analyzing genomic DNA from HRT-25 based on the data from 3'-RACE, we have clarified the breaking point in HPRT1 intron 3 and following an unknown sequence of 1007-bp. We analyzed HPRT1 genomic DNA in order to confirm the mutation with an unknown sequence in the genomic DNA. Unknown sequence compared through BLAST analysis of the human genome(NCBI; http://www.ncbi.nlm.nih.gov/BLAST/)showed that at least 0.5 to 0.6-Mb telomeric to HPRT1 on chromosome Xq wherel ocated near LOC340581. In the genomic DNA form HRT-25, a translocation between HPRT1 and the otherr egiono n the X chromosomei nvolvesa chimerag ene structureth at lost a region of downstream from intron3 of HPRT1. This study demonstratesth e molecularb asis for the involvemenot f genomici nstabilityin germc ells.
