A new gene-pseudogene fusion allele due to a recombination in intron 2 of the glucocerebrosidase gene causes Gaucher disease

Gaucher disease is the most prevalent sphingolipid storage disorder in huma ns caused by a recessively inherited deficiency of the enzyme glucocerebros idase. More than 100 mutations have been described in the glucocerebrosidas e gene causing Gaucher disease. Some of them are complex alleles with sever al mutations due to recombination events between the gene and its highly ho mologous pseudogene. The generation of these recombinant alleles involves, in most cases, a crossover in the 3' end of the gene, beyond exon 8. Howeve r, in a few cases recombination took place in a more upstream location. Her e we describe the analysis of a patient with type I Gaucher disease who bea rs a new complex allele. This allele was originated by a crossover between the gene and the pseudogene at intron 2, the most upstream recombination si te described so far, which gave rise to a fusion gene. The patient was firs t diagnosed as homozygous for the c.1226 A --> G (N370S) mutation but the e arly onset of the disease prompted us to perform parental DNA analysis whic h showed that the mother was not a N370S carrier, suggesting deletion of at least part of the gene. Molecular analysis of the complex allele was carri ed out by Southern blot, PCR, and sequencing. We were able to close down th e region of the recombination event to an interval of 18 nucleotides, corre sponding to the last 15 nucleotides of intron 2 and the first 3 nucleotides of exon 3 of the gene. These 18 nucleotides are identical between the gene and pseudogene making any further refinement impossible. An exhaustive lis t of published glucocerebrosidase complex alleles, describing their recombi nation points, is included for comparison, (C) 2000 Academic Press.