21-hydroxylase deficiency: disease-causing mutations categorized by densitometry of 21-hydroxylase-specific deoxyribonucleic acid fragments.
The types of disease-causing mutations were studied in 43 unrelated patients with 21-hydroxylase deficiency. Densitometry of Southern blots after cleavage with the restriction enzymes TaqI, PvuII, and BglII was used to measure the ratio of the copy-number of the 21-hydroxylase gene (CYP21) to the copy-number of its pseudogene (CYP21P). DNA from 16 unrelated patients showed equal hybridization intensities of the 2 genes, indicating that point mutations caused the enzyme deficiency. One of the 2 haplotypes in 7 patients showed evidence of a large gene conversion between the CYP21 and the CYP21P gene without loss of the total number of 21-hydroxylase genes. Deletion of at least 1 21-hydroxylase gene was found in 11 patients. DNA from 8 of these patients had relative hybridization intensities compatible with a deletion of the active 21-hydroxylase gene, CYP21. Two patients with the salt-wasting form of the disease showed homozygous loss of DNA fragments that are specific for the 5' end of the active 21-hydroxylase gene. Nine patients showed relative 21-hydroxylase hybridization intensities compatible with duplication of the gene in 1 or both haplotypes. In conclusion, point mutations, gene conversions, or CYP21 gene deletions are the typical mutations in patients with the simple virilizing and salt-wasting forms of the disease, while duplications of the locus are overrepresented in patients with nonclassical 21-hydroxylase deficiency.
Haglund-Stengler
B
B
Department of Clinical Genetics, Karolinska Institutet, Karolinska Hospital, Stockholm, Sweden.
Ritzén
E M
EM
Luthman
H
H
D000312:Adrenal Hyperplasia, Congenital / Q000201:enzymology* / Q000235:genetics; D015139:Blotting, Southern; D004247:DNA / Q000032:analysis*; D004262:DNA Restriction Enzymes; D003720:Densitometry; D005796:Genes; D005838:Genotype; D006801:Humans; D009154:Mutation; D009693:Nucleic Acid Hybridization; D013255:Steroid 21-Hydroxylase / Q000235:genetics / Q000302:isolation & purification; D013250:Steroid Hydroxylases / Q000172:deficiency*
D004247:DNA; D013250:Steroid Hydroxylases; D013255:Steroid 21-Hydroxylase; D004262:DNA Restriction Enzymes