Molecular description of three macro-deletions and an Alu-Alu recombination-mediated duplication in the HPRT gene in four patients with Lesch-Nyhan disease.
Mutations in the HPRT gene cause a spectrum of diseases that ranges from hyperuricemia alone to hyperuricemia with profound neurological and behavioral dysfunction. The extreme phenotype is termed Lesch-Nyhan syndrome. In 271 cases in which the germinal HPRT mutation has been characterized, 218 different mutations have been found. Of these, 34 (13%) are large- (macro-) deletions of one exon or greater and four (2%) are partial gene duplications. The deletion breakpoint junctions have been defined for only three of the 34 macro-deletions. The molecular basis of two of the four duplications has been defined. We report here the breakpoint junctions for three new deletion mutations, encompassing exons 4-8 (20033bp), exons 4 and 5 (13307bp) and exons 5 and 6 (9454bp), respectively. The deletion breakpoints were defined by a combination of long polymerase chain reaction (PCR) amplifications, and conventional PCR and DNA sequencing. All three deletions are the result of non-homologous recombinations. A fourth mutation, a duplication of exons 2 and 3, is the result of an Alu-mediated homologous recombination between identical 19bp sequences in introns 3 and 1. In toto, two of three germinal HPRT duplication mutations appear to have been caused by Alu-mediated homologous recombination, while only one of six deletion mutations appears to have resulted from this type of recombination mechanism. The other five deletion mutations resulted from non-homologous recombination. With this admittedly limited number of characterized macro-mutations, Alu-mediated unequal homologous recombinations account for at least 8% (3 of 38) of the macro-alterations and 1% (3 of 271) of the total HPRT germinal mutations.
Brooks
E M
EM
Genetics Laboratory, University of Vermont, 32 N. Prospect Street, Burlington, VT 05401, USA.
Branda
R F
RF
Nicklas
J A
JA
O'Neill
J P
JP
D020087:Alu Elements; D001483:Base Sequence; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D016208:Databases, Factual; D005091:Exons; D020440:Gene Duplication; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D007438:Introns; D007926:Lesch-Nyhan Syndrome / Q000201:enzymology* / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid
D017931:DNA Primers; D018076:DNA, Complementary; D007041:Hypoxanthine Phosphoribosyltransferase