P450XXI (steroid 21-hydroxylase) gene deletions are not found in family studies of congenital adrenal hyperplasia.

Abstract

Congenital adrenal hyperplasia (CAH) is a common genetic disorder due to defective 21-hydroxylation of steroid hormones. The human P45OXXIA2 gene encodes cytochrome P450c2l [steroid 21-monooxygenase (steroid 21-hydroxylase), EC 1.14.99.10], which mediates 21-hydroxylation. The P45OXXIA2 gene may be distinguished from the duplicated P45OXXIA1 pseudogene by cleavage with the restriction endonuclease Taq I, with the XXIA2 gene characterized by a 3.7-kilobase (kb) fragment and the XXIA1 pseudogene characterized by a 3.2-kb fragment. Restriction endonuclease mapping by several laboratories has suggested that deletion of the P45OXXIA2 gene occurs in about 25% of patients with CAH, as their genomic DNA lacks detectable 3.7-kb Taq I fragments. We have cloned human P450c21 cDNA and used it to study genomic DNA prepared from 51 persons in 10 families, each of which includes 2 or more persons with CAM. After Taq I digestion, apparent deletions are seen in 7 of the 20 alleles of the probands; using EcoRI, apparent deletions are seen in 9 of the 20 alleles. However, the apparently deleted alleles seen with Taq I do not coincide with those seen with EcoRI. Furthermore, studies with Bgl II, EcoRI, Kpn I, and Xba I yield normal patterns with at least two enzymes in all cases. Since all probands yielded normal patterns with at least two of the five enzymes used, we conclude that the P45OXXIA2 gene "deletions" widely reported in CAH patients probably represent gene conversions, unequal crossovers, or polymorphisms rather than simple gene deletions.

Transcript encoded on the opposite strand of the human steroid 21-hydroxylase/complement component C4 gene locus.

“…The 3' end of the 2.7-kb cDNA was identified by a 13-base poly(A) tail; the adjacent DNA had a nucleotide sequence identical to that of the antisense strand of the 3' untranslated region of the P450c21 gene and contained the AATAAA sequence in the predicted location. Therefore, the 2.7-kb cDNA was encoded by a gene on the opposite DNA strand from the P450c21 and C4 genes that had a transcriptional initiation site downstream from the P450c21 locus and whose 3' end overlapped P450c21 exon 10 (Fig. 2).…”

CYP21 and CYP21P variability in steroid 21-hydroxylase deficiency patients and in the general population in the Netherlands

“…Analysis of TaqI and BglII restriction patterns is commonly used to determine the gross arrangement of the CYP21/C4 region in steroid 21-hydroxylase deficiency patients and their family members. 1,[9][10][11][12][13][14][15] This approach allows the definition of CYP21/C4 haplotypes, some of which are associated with steroid 21-hydroxylase deficiency. [14][15][16][17][18][19][20][21][22] .…”

“…10,12,13 (c) Haplotypes where a gene with a CYP21-like restriction pattern is present (by exclusion).…”

Characterization of frequent deletions causing steroid 21-hydroxylase deficiency.

“…1), CYP21A is associated with 3.2-kb (and 2.4-kb) Taq I, 4.0-kb Kpn I, and 2.0-kb Bgl II/EcoRI fragments, while CYP21B carries 3.7-kb (and 2.5-kb) Taq I, 2.9-kb Kpn I, and 2.4-kb Bgl II/EcoRI fragments (densitometry was not performed on 2.4-and 2.5-kb Taq I bands because they were weak and poorly resolved). To make it easier to compare our results with other studies (10,11,14), Taq I and Kpn I digests were hybridized with the 1500-bp EcoRI/BamHI cDNA fragment, while Bgl II/EcoRI digests were hybridized with the 3.7-kb Taq I genomic fragment. Partial or full-length cDNA and genomic probes could be used interchangeably in Results of hybridization of Taq I digests with a C4 probe are also shown, with C4B intensities (5.4, 6.0, or 6.3 kb) divided by C4A intensities (7.0 kb).…”