Elsevier

Metabolism

Volume 60, Issue 10, October 2011, Pages 1386-1391
Metabolism

Three novel CYP17A1 gene mutations (A82D, R125X, and C442R) found in combined 17α-hydroxylase/17,20-lyase deficiency

https://doi.org/10.1016/j.metabol.2011.03.008Get rights and content

Abstract

The aim of this study was to analyze the structure and functional consequences of 3 novel mutations (A82D, R125X, and C442R) of the CYP17A1 gene found in 2 patients with combined 17α-hydroxylase/17,20-lyase deficiency (17OHD). Two Chinese 46, XY female patients were diagnosed with 17OHD based on clinical findings and biochemical results. The CYP17A1 gene was analyzed by polymerase chain reaction direct sequencing. An in vitro expression system was performed in HEK293 cells to analyze the mutant P450c17 activity compared with the wild type. Analysis of the CYP17A1 gene sequences in patient 1 showed compound heterozygous mutations A82D (g.417 C > A) in exon 1 and Y329fs (g.4869 T > A, 4871del) in exon 6; DNA sequencing analysis in patient 2 revealed compound heterozygous mutations R125X (g.2045 C > T) in exon 2 and C442R (g.6457 T > C) in exon 8. The mutations A82D, R125X, and C442R have not been reported previously. The functional study demonstrated that the A82D, R125X, and C442R mutations almost completely eliminate enzymatic activity. These results, which indicate that Ala 82 and Cys 442 are crucial for both 17-hydroxylase and 17,20-lyase activities, help define the structure-function relationship of the CYP17A1 gene. The novel mutations A82D, R125X, and C442R further clarify the patients' clinical manifestations of combined 17OHD.

Introduction

Congenital adrenal hyperplasia resulting from combined 17α-hydroxylase/17, 20-lyase deficiency (17OHD) is a rare autosomal recessive disease with an approximate incidence of 1:50 000 to 1:100 000 in newborns [1]. 17α-Hydroxylase is the key enzyme required for the synthesis of cortisol; it catalyzes the 17α-hydroxylation reaction of progesterone and pregnenolone into 17α-hydroxyprogesterone and 17α-hydroxypregnenolone, respectively. Impaired 17α-hydroxylase activity leads to decreased cortisol synthesis and compensatory hypersecretion of adrenocorticotropic hormone (ACTH). The excess ACTH stimulates hyperplasia of bilateral adrenal glands and overproduction of mineralocorticoids such as 11-deoxycorticosterone, which causes hypertension, hypokalemia, and suppressed plasma renin and aldosterone activity in 17OHD patients [2], [3]. 17,20-Lyase is essential to the production of sex steroids; it converts 17α-hydroxyprogesterone and 17α-hydroxypregnenolone into androstenedione and dehydroepiandrosterone (DHEA), respectively, the precursors of sex hormone. A defect in 17,20-lyase results in the insufficient sex hormone production, causing 17OHD patients to have an absence of pubertal development and disorders of sex development [2], [3], [4]. All patients present with the female phenotype, but have varied genotypes: 46, XX individuals (genotypic female) show primary amenorrhea and lack of secondary sex characteristics; 46, XY individuals (genotypic male) always present with infantile female or ambiguous external genitalia and intraabdominal or inguinal testes, but no uterus, oviduct, or upper part of the vagina due to normal Müllerian duct inhibition.

Both 17α-hydroxylase and 17,20-lyase are encoded by one human CYP17A1 gene, which resides in 10q24.3 and is expressed in several steroidogenic tissues, including the adrenal cortex, ovaries, and testes [5], [6]. To date, approximately 90 mutations, including missense mutations, nonsense mutations, insertions, deletions, and splice site defects, have been reported in 17OHD patients (www.hgmd.cf.ac.uk/ac/gene.php?gene=CYP17A1). Because the severity of clinical manifestations in 17OHD is determined by the residual mutant P450c17 enzyme activity, the mutations affecting the heme binding site or steroid substrate binding site often demonstrate combined 17α-hydroxylase/17,20-lyase deficiency, whereas the mutations affecting the redox-partner binding site only lead to isolated 17,20-lyase deficiency [7], [8]. Therefore, the mutations in the CYP17A1 gene, especially point mutations, directly reflect the functions of the given amino acid in the P450c17 enzyme.

Although the imperfect activity of P450c17 caused by CYP17A1 gene mutations cannot be restored, the symptoms such as hypertension and hypokalemia can be reversible with the treatment of exogenous glucocorticoid, such as prednisone, by inhibiting the hypersecreted ACTH. 46, XX patients are treated with the addition of conjugated estrogens to retain secondary sex characteristics; 46, XY patients are further advised to undergo a cryptorchidectomy in case of malignant tumors of the testes, owing to the irreversible malformation of external and internal genitalia, as well as psychological factors [9], [10], [11].

Here, we describe 2 combined 17OHD 46, XY female patients with 3 novel mutations (A82D, R125X, and C442R), which provide further insights to CYP17A1 gene functions.

Section snippets

Case report

Table 1 summarizes the clinical, biochemical, and hormonal findings in the 2 patients.

Serum steroid hormone concentration results

Results are shown in Table 1.

Mutation analysis

Direct sequencing analysis of the CYP17A1 gene in patient 1 revealed a compound heterozygous state in exon 1 and exon 6 (Fig. 1A). The novel missense mutation in exon 1 (g.417 C > A) results in a substitution from alanine to aspartic acid at amino acid position 82 (A82D). The mutation in exon 6 (g.4869 T > A, 4871del; Y329fs) was reported previously [12]. Segregation analysis showed that A82D was a maternal inheritance and that Y329fs (g.4869 T > A, 4871del) was a

Discussion

We report 2 Chinese patients with combined 17OHD caused by novel mutations in the CYP17A1 gene. The mutations A82D, R125X, and C442R have not been reported previously. In vitro functional experiments of these mutations provided strong evidence for the pathological effect of the identified mutations.

The missense A82D mutation substitutes the conserved neutral alanine residue to an acidic aspartic acid residue. Functional expression analysis revealed that this mutation only retained 3.5% of

Acknowledgment

We thank Dr. Qiang Li (Laboratory Medicine, China Medical University affiliated Shengjing Hospital, Shenyang, PR China) for assistance with high-performance liquid chromatography experiments and data analysis.

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    Author contributions: Yue-Ping Wang designed and performed the experiments (CYP17A1 gene mutation analysis and in vitro function study) and wrote the manuscript. Jing Li and Jian-Xin Li collected clinical information from 2 patients. Yun-Jing Zhao and Dan-Ye Zhang performed DNA extractions and partial polymerase chain reaction amplifications.

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