A new compound heterozygous mutation in the CYP17A1 gene in a female with 17α-hydroxylase/17,20-lyase deficiency

Functional Identification of Compound Heterozygous Mutations in the CYP17A1 Gene Resulting in Combined 17α-Hydroxylase/17,20-Lyase Deficiency

BACKGROUND

We previously reported a patient with congenital adrenal hyperplasia (CAH) with compound heterozygous mutations in the cytochrome P450 17A1 (CYP17A1) gene. One allele had a p.His373Leu and the other a new p.Glu383fsX36 mutation. The aim of this study was to investigate the functional properties of a new allele present in a compound heterozygote of CYP17A1.

METHODS

To understand how p.His373Leu and p.Glu383fsX36 affect P450c17 enzymatic activity, wild type and mutant CYP17A1 cDNAs were cloned into flag-tagged pcDNA3 vector and introduced into human embryonic kidney cells 293T (HEK293T) cells. Protein expression levels of CYP17A1 were then analyzed. And the activities of 17α-hydroxylase and 17,20-lyase of CYP17A1 were evaluated by measuring the conversion of progesterone to 17α-hydroxyprogesterone and of 17α-hydroxypregnenolone to dehydroepiandrosterone, respectively. In addition a computer model was used to create the three-dimensional structure of the mutant CYP17A1 enzymes.

RESULTS

Production of the p.His373Leu mutant protein was significantly lower than that of the wild type protein, and the p.Glu383fsX36 protein was hardly produced. Similarly the enzymatic activity derived from the p.His373Leu mutant vector was significantly lower than that obtained from the wild type vector, and little activity was obtained from the p.Glu383fsX36 vector. Three-dimensional modeling of the enzyme showed that p.His373 was located in region important for heme-binding and proper folding. Neither the p.His373Leu nor the p.Glu383fsX36 mutant protein formed a heme-binding structure.

CONCLUSION

Enzyme activity measured in both mutants disappeared completely in both 17α-hydroxylase and 17,20-lyase. This result accounts for the clinical manifestations of the patient with the compound heterozygous CYP17A1 mutations.

The Glu331del mutation in the CYP17A1 gene causes atypical congenital adrenal hyperplasia in a 46,XX female

17α-Hydroxylase deficiency is an uncommon type of congenital adrenal hyperplasia (CAH) caused by mutations in the CYP17A1 gene encoding both 17α-hydroxylase and 17,20-lyase, essential for sex steroids production. Main clinical features include lack of pubertal development, hypertension, and hypokalemia. We report the first case of a 46,XX female homozygote for the p.Glu331del mutation in the CYP17A1 gene showing an atypical clinical presentation. She was evaluated the first time for primary amenorrhea and delayed puberty in the presence of low levels of androgens, 17β-estradiol, serum cortisol, and high levels of progesterone and gonadotropins. After puberty, the patient did not show hypocortisolism and/or hypertension. She started estrogen therapy for pubertal induction, followed by ethinylestradiol/gestodene with clinical and biochemical stability during the follow-up period. At the age of 40 years, she developed hypokalemia and clinical signs of hypocortisolism. Oral corticosteroid treatment was started showing a prompt clinical improvement. Modeling analysis predicted the main outcome of the E331 deletion to impair cytochrome b5 binding, according to a major effect on the enzyme's lyase activity. These data broaden the molecular and clinical spectrum of CAH caused by 17α-hydroxylase deficiency and adds to current genotype-phenotype correlations.

Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1)

Cytochrome b5 (cyt b5) is a small hemoprotein that plays a significant role in the modulation of activities of an important steroidogenic enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1, CYP17A1). Located in the zona fasciculata and zona reticularis of the adrenal cortex and in the gonads, P450 17A1 catalyzes two different reactions in the steroidogenic pathway; the 17α-hydroxylation and 17,20-lyase, in the endoplasmic reticulum of these respective tissues. The activities of P450 17A1 are regulated by cyt b5 that enhances the 17,20-lyase reaction by promoting the coupling of P450 17A1 and cytochrome P450 reductase (CPR), allosterically. Cyt b5 can also act as an electron donor to enhance the 16-ene-synthase activity of human P450 17A1. In this review, we discuss the many roles of cyt b5 and focus on the modulation of CYP17A1 activities by cyt b5 and the mechanisms involved.

Congenital Adrenal Hyperplasia due to 17-alpha-hydoxylase/17,20-lyase Deficiency Presenting with Hypertension and Pseudohermaphroditism: First Case Report from Oman

This is the first report of congenital adrenal hyperplasia (CAH) due to combined 17α-hydroxylase/17,20 lyase deficiency in an Omani patient who was initially treated for many years as a case of hypertension. CAH is an uncommon disorder that results from a defect in steroid hormones biosynthesis in the adrenal cortex. The clinical presentation depends on the site of enzymatic mutations and the types of accumulated steroid precursors. A 22-year-old woman who was diagnosed to have hypertension since the age of 10 years who was treated with anti-hypertensive therapy was referred to the National Diabetes and Endocrine Centre, Royal Hospital, Oman. The patient also had primary amenorrhea and features of sexual infantilism. Full laboratory and radio-imaging investigations were done. Adrenal steroids, pituitary function and karyotyping study were performed and the diagnosis was confirmed by molecular mutation study. Laboratory investigations revealed adrenal steroids and pituitary hormones profile in addition to 46XY karyotype that are consistent with the diagnosis of CAH due to 17α-hydroxylase deficiency. Extensive laboratory workup revealed low levels of serum cortisol (and its precursors 17α-hydroxyprogesterone and 11-deoxycortisol), adrenal androgens (dehydroepiandrosterone sulfate and androstenedione), and estrogen (estradiol); and high levels of mineralocorticoids precursors (11-deoxycorticosterone and corticosterone) with high levels of ACTH, FSH and LH. Mutation analysis revealed CYP17A1-homozygous mutation (c.287G>A p.Arg96Gln) resulting in the complete absence of 17α-hydroxylase/17,20-lyase activity. The patient was treated with dexamethasone and ethinyl estradiol with cessation of anti-hypertensive therapy. A review of the literature was conducted to identify previous studies related to this subtype of CAH. This is the first biochemically and genetically proven case of CAH due to 17α-hydroxylase/17,20-lyase deficiency in Oman and in the Arab World described in the literature.

Clinical and genetic analyses of a Chinese female with 17α-hydroxylase/17,20-lyase deficiency

AIMS

17α-Hydroxylase/17,20-lyase deficiency (17OHD) is a rare autosomal recessive disease caused by CYP17 gene mutations. This disease is clinically characterised by hypertension, hypokalaemia, sexual infantilism in females or pseudohermaphroditism in males, and adrenal hyperplasia. This study aims to investigate a rare case of 17OHD accompanied by both cystic ovaries and massive adrenal mass.

METHODS

This study performed clinical, hormonal, radiological and genetic analyses. Blood samples were collected from the patient for the genetic test. Genomic DNA was extracted from peripheral blood leukocytes, and the coding sequence abnormalities of CYP17 were assessed using polymerase chain reaction and direct sequencing analysis.

RESULTS

The genetic analysis of CYP17 revealed compound heterozygous mutations in the individual. One was a mis-sense mutation of c.1226 C > G, which changes codon 409 in exon 7 from proline (CCG) to arginine (CGG). Another was a mutation of p.Val311Asp,fs,330X, which was first reported in a compound heterozygote mutation of Y329fs and V311fs from a Chinese patient.

CONCLUSION

This study presented a rare case of 17OHD accompanied by both cystic ovaries and massive adrenal mass. This study obtained significant information on the genotype-phenotype correlation of 17OHD.