CYP21A2 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: CYP21A1P shares 98% sequence identity with CYP21A2. Due to the high degree of sequence identity between the gene and its pseudogene, most of the disease-causing mutations described in 21-hydroxylase deficiency are likely to be the consequence of non-homologous recombination or gene conversion events6, 7.