A de novo pathological point mutation at the 21–hydroxylase locus: implications for gene conversion in the human genome

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Abstract
More than two hundred characterized 21–hydroxylase deficiency alleles appear to result exclusively from sequence exchanges involving the 21–hydroxylase gene (CYP21B) and a closely related pseudogene (CYP21A). Gene conversion–like events have also been reported in many other human gene clusters, but in the absence of a de novo mutation, the alternative explanation of a multiple recombination is possible. We now report a de novo pathological mutation at the 21–hydroxylase locus. DNA sequence analysis suggests that the mutation arose by a microconversion event involving exchange of up to 390 nucleotides between maternal CYP21A and CYP21B genes. This putative de novo gene conversion event appears to be the first characterized in humans.