Isolated 17,20-lyase deficiency due to the cytochrome b5 mutation W27X.

CONTEXT: Cytochrome P450c17 (P450c17) is a bifunctional enzyme necessary for the production of glucocorticoids (17-hydroxylase activity) and sex steroids (17,20-lyase activity). Isolated 17,20-lyase deficiency is a rare condition characterized by a deficient production of androgens resulting in 46,XY disorders of sex development (DSD) while the production of glucocorticoids is intact. Several missense mutations in the CYP17A1 gene are known to cause this condition. Cytochrome b(5) (CytB5) is an important factor in 17,20-lyase activity, probably by acting as an allosteric factor. OBJECTIVE: The aim of this study was to investigate the role of CytB5 in a patient with defective 17,20-lyase activity. SETTING: We conducted the study in a pediatric outpatient clinic of a University Hospital. PATIENTS: We studied a 46,XY DSD patient with 17,20-lyase deficiency without missense mutation in the CYP17A1 gene and his parents. MAIN OUTCOME MEASURES: We sequenced the CYB5 gene and measured steroid hormone levels. RESULTS: Analysis of the CYB5 gene in our patient revealed a homozygous W27X mutation, leading to the formation of a premature stop codon; his parents were both heterozygous carriers of this mutation. This mutation results in the absence of residues E48 and E49 of CytB5, which are necessary for an intact 17,20-lyase activity. CONCLUSION: We demonstrated 17,20-lyase deficiency due to an aberrant CytB5. Our findings thus provide evidence for an alternative etiology for this disorder.

Lack of correlation between phenotype and genotype in untreated 21-hydroxylase-deficient Indonesian patients.

BACKGROUND: Mutations in CYP21A2 lead to deficiency of 21-hydroxylase and can have either severe or moderate effects on phenotype, which can be prevented by early treatment. We studied long-term effects of this deficiency on phenotype in patients who had not been treated for prolonged periods and correlated these phenotypes with the mutations found in our patients. OBJECTIVE: To assess the correlation between genotype and phenotype in untreated patients with 21-hydroxylase deficiency. DESIGN: Subjects with 21-hydroxylase deficiency were selected from a large population of Indonesian patients with disorders of sexual differentiation. CYP21A2 mutations in these patients were correlated with their phenotype in terms of genital development and steroid hormone levels. PATIENTS: Fifteen 46,XX patients with ages between 1 and 33 years, of whom 12 had never been treated before. MEASUREMENTS: Mutations in CYP21A2, genital phenotype and steroid hormone levels. RESULTS: We found in all patients CYP21A2 mutations which affect enzyme activity, with a relatively high allele frequency of R356W (40%), I172N (20%) and IVS2 - 1A > G (13%). Clitoris length was directly correlated with levels of testosterone, but not with age. The phenotype was not always concordant with the genotype: different phenotypes (mild to severe virilization) were found in sibling pairs with the mutations IVS2 - 13A > G or I172N. The high frequency of homozygous mutants for R356W in patients aged from 1 to 11 years old is remarkable, as this mutation has been described only in salt-wasting patients. In our study, this mutation caused a urogenital sinus in three out of seven cases, whereas in the remaining cases the labia were at least partially fused. This mutation caused severe virilization with remarkably high serum levels of renin. We found one novel substitution in intron 2 (IVS2 - 37A > G), containing the branch site, which is likely to affect the CYP21-enzyme. Two additional intron 2 substitutions were discovered, which are supposed to affect the 21-hydroxylase (i.e. IVS2 + 33A > C and IVS2 + 67C > T). CONCLUSION: We conclude that a correlation exists between the concentration of androgens and the extent of virilization. However, there was no clear correlation between genotype and phenotype, except for the mutation R356W.

Differential inhibition of 17alpha-hydroxylase and 17,20-lyase activities by three novel missense CYP17 mutations identified in patients with P450c17 deficiency.

The microsomal enzyme cytochrome P450c17 is an important regulator of steroidogenesis. The enzyme has two functions: 17alpha-hydroxylase and 17,20-lyase activities. These functions determine the ability of adrenal glands and gonads to synthesize 17alpha-hydroxylated glucocorticoids (17alpha-hydroxylase activity) and/or sex steroids (17,20-lyase activity). Both enzyme functions depend on correct steroid binding, but it was recently shown that isolated lyase deficiency can also be caused by mutations located in the redox partner interaction domain. In this article we present the clinical history and molecular analysis of two patients with combined 17alpha-hydroxylase/17,20-lyase deficiency and four patients with isolated 17,20-lyase deficiency. In these six patients, four missense CYP17 mutations were identified. Two mutations were located in the steroid-binding domain (F114V and D116V), and the other two mutations were found in the redox partner interaction domain (R347C and R347H). We investigated the activity of these mutated proteins by transfection experiments in COS-1 cells using pregnenolone, progesterone, or their hydroxylated products as a substrate and measuring 17alpha-hydroxylase- and 17,20-lyase-dependent metabolites in the medium. The mutations in the steroid-binding domain (F114V and D116V) of P450c17 caused combined, complete (F114V), or partial (D116V) 17alpha-hydroxylase and 17,20-lyase deficiencies, whereas mutations in the redox partner interaction domain (R347C and R347H) displayed less severe 17alpha-hydroxylase deficiency, but complete 17,20-lyase deficiency. These findings are consistent with the clinical data and support the observation that the redox partner interaction domain is essential for normal 17,20-lyase function of P450c17.