Use of PCR-based amplification analysis as a substitute for the southern blot method for CYP21 deletion detection in congenital adrenal hyperplasia.

Abstract

Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disorder caused mainly by defects in the steroid 21-hydroxylase gene (CYP21) . The defective CYP21 genes in CAH fall into one of three categories: (a) small-scale conversions from CYP21P ; (b) spontaneous mutations; and (c) chimeric RCCX modules that include the chimeric CYP21P / CYP21 gene (1) and the chimeric TNXA/TNXB gene (2)(3)(4). The RCCX module in chromosome 6p21.3 of the human MHC class III region is composed of a part of the RP gene (serine/threonine nuclear protein kinase) (5), a full-complement C4 gene, a full CYP21 (P) gene, and a portion of the TNX gene (6)(7). The C4 protein is coded by two genes, C4A and C4B . The occurrence of a long (20.4 kb) or short (14.1 kb) C4 gene is attributable to the presence of an endogenous retroviral sequence (6.7 kb), namely HERV-K (C4), in intron 9 (8). The TNX gene contains XA (TNXA) and TNXB . TNXB , in the downstream CYP21 gene, is partially duplicated in the downstream CYP21P gene, where a truncated gene is termed TNXA . Both TNXA and TNXB are transcribed on the opposite strand. There are two RP genes, RP1 and RP2 . The RP2 gene is truncated and corresponds to RP1 adjacent to TNXA . These genes are arranged in the RP1-C4A-CYP21P-XA-RP2-C4B-CYP21-TNXB gene sequence and are designated as the bimodule of RCCX (Fig. 1A⇓ ). The bimodule is composed of a long module including part of RP1 , C4A (long), CYP21P , and TNXA , and a short module containing RP2 , C4B (short), CYP21 , and part of the TNXB gene (2) (Fig. 1A⇓ ). In Caucasians, the RCCX module has three possible forms: monomodule, bimodule, and trimodule; the bimodular form is …