CYP21A1P and congenital adrenal hyperplasia: In CAH, the vast majority of pathogenic alleles are due to two mechanisms: pseudogene minor conversion, resulting in 12 common variants of CYP21A1P origin and unequal crossovers, resulting in chimeric genes (also termed 30-kb deletions), accounting for 60% and 30% of allele frequency, respectively [3,18,19,20,21].