Steroid 21-hydroxylase deficiency is caused by mutations in the CYP21 gene, Approximately 95% of mutant alleles are generated by recombination events between the acitve gene CYP21 and its highly homologous pseudogene, CYP21P. Deletion alleles are generated by unequal crossing over, while point mutations are the result of gene conversion events. Deletions account for 20-25% of the 21-hydroxylase deficiency alleles in most populations studied. We have looked for deletions among 53 unrelated Mexican patients with steroid 21-hydroxylase deficiency and found that deletions represent less than 1% of the disease alleles. These findings suggest that nearly all mutant alleles in our patient population contain point mutations and that the low representation of deletion alleles among clinically diagnosed patients may be due to missing detection of salt wasters, mainly males, who may die during the neonatal period.
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