The 3.7- and 3.2-kb fragments produced by TaqI digestion are respective crucial markers of the CYP21A2 and CYP21A1P genes for the analysis of the RCCX module in chromosome 6p21.3. Herein, we report two distinct CYP21A2 haplotypes. One occurred in a CAH patient with a 6.2-kb TaqI fragment caused by a mutation at the TaqI site (TCGA) located downstream of the CYP21A2 gene, and the other was a parent in a suspected CAH family with a 3.2-kb TaqI fragment resulting from a 156-bp fragment conversion of the CYP21P promoter sequence which led to the production of a TaqI site at nt −209 and two additional CYP21A1P nucleotides at nt −198 (C > T) and −188/−189 (T insertion). From further sequencing analysis, the promoter region of the 3.2-kb allele showed four normal transcriptional sequences positioned at nt −126C, −113G, −110T, and −103A. However, other nucleotides such as at nt −294T, −293A, and −282A were unchanged. We concluded that the 6.2-kb TaqI fragments of the CYP21A2 haplotype may lead to an incorrect result in the analysis between CYP21A2 and CYP21A1P. The formation of the 3.2-kb TaqI fragment allele which can be mistaken for the CYP21A1P gene may be caused by small-scale conversions of the CYP21A1P gene located between nt −126C and −282A. Therefore, the CYP21A2 haplotype not only presents a 3.7-kb TaqI fragment but also may possibly exist in multiple forms including both 6.2- and 3.2-kb fragments.
