A Mutation (Pro-30 to Leu) inCYP21 Represents a Potential Nonclassic Steroid 21-Hydroxylase Deficiency Allele

Abstract

The mild nonclassic form of steroid 21-hydroxylase deficiency is one of the most common autosomal recessive disorders in humans, occurring in almost 1% of caucasians and about 3% of Ashkenazi Jews. Many patients with this disorder carry a Val-281----Leu missense mutation in the CYP21 gene. This and most other mutations causing 21-hydroxylase deficiency are normally present in the CYP21P pseudogene and have presumably been transferred to CYP21 by gene conversion. To identify other potential nonclassic alleles, we used recombinant vaccinia virus to express two mutant enzymes carrying the mutations Pro-30----Leu (normally present in CYP21P) and Ser-268----Thr (considered a normal polymorphism of CYP21). Whereas the activity of the protein carrying the Ser----Thr mutation was indeed indistinguishable from the wild type, the enzyme with the Pro----Leu substitution had 60% of wild-type activity for 17-hydroxyprogesterone and about 30% of normal activity for progesterone when assayed in intact cells. When kinetic analysis of the latter mutant enzyme was performed in cellular lysates, the first order rate constants (maximum velocity/dissociation constant) for both substrates were reduced 10- to 20-fold compared with those for the wild-type enzyme. Pro-30 is conserved in many microsomal P450 enzymes and may be important for proper orientation of the enzyme with respect to the aminoterminal transmembrane segment. The Pro----Leu mutation was present in 5 of 18 patients with nonclassic 21-hydroxylase deficiency, suggesting that this mutation indeed acts as a nonclassic deficiency allele.

Structure–phenotype correlations of human CYP21A2 mutations in congenital adrenal hyperplasia

“…We show that this in silico approach can predict the extent of loss of function of the steroidogenic CYP21A2 enzyme. With certain mutations, varying degrees of loss of function have been confirmed biochemically by overexpressing the mutated enzyme in vitro (27)(28)(29)(30)(31)(32), whereas, in other cases, the extent to which the enzyme is disrupted remains unknown.…”

Mutational spectrum of congenital adrenal hyperplasia in Slovenian patients: a novel Ala15Thr mutation and Pro30Leu within a larger gene conversion associated with a severe form of the disease

“…Already the first report on Pro30Leu emphasises that affected females frequently present with clitoromegaly (26). Many authors later reported observations of more severe clinical phenotype than predicted by genotyping in carriers of Pro30Leu mutation (10,11,22).…”

Genetics of Congenital Adrenal Hyperplasia

“…[30][31][32] Mutations in p.V281L, p.P453S and p.P30L cause an interference in oxidoreductase interactions, salt-bridge and hydrogen bonding networks, and produce enzymes retaining 20-60% of normal activity as seen in NCCAH (Group C). 21,33,34 In general, there is good genotype-phenotype correlation for the NCCAH p.V281L and p.P453S mutations, but phenotypic variability has been described for p.P30L. 6,24 Uncommon chimeric genes also account for some genotype-phenotype discrepancy and the junction site of the chimeras that develop as a consequence of genetic rearrangements can be (Figure 3).…”