Techatraisak, Kitirat; (1996) Molecular analysis of the 17alpha-hydroxylase gene and its potential role in hyperandrogenism. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The steroid 17α-hydroxylase (CYP17) enzyme plays a pivotal role in the synthesis of the glucocorticoids and the sex steroid hormones. The identification of naturally occurring mutations and polymorphisms is therefore of considerable importance to our understanding of the structure and function of the enzyme and its possible role in the development of hyperandrogenic states. This project had two aims: firstly to identify mutations in patients with CYP17 deficiency and secondly to explore the hypothesis that polymorphic variants in the CYP17 promoter and/or coding regions exist. Such variants may modify expression of the gene leading to interindividual variation in androgen production. The technique of single strand conformation polymorphism (SSCP) analysis was used to screen variants in genomic DNA samples from 4 patients with CYP17 deficiency and hyperandrogenic individuals. Two different detection systems, namely silver staining and 32P-labelling were compared for sensitivity. Cloning and sequencing were subsequently performed to identify the sequence variations. The two detection techniques gave similar results, with silver staining showing slightly greater sensitivity. Variant SSCP patterns were found in all four patients but in only two were pathological mutations identified. Two of these were single base pair substitutions causing the missense mutations arg96trp (exon 1) and thrl31ser (exon 2) and the third, a 5 bp deletion in exon 7 leading to a premature termination codon at codon 387. Seven polymorphisms were identified of which three have not previously been described. The prevalence of a polymorphism in the 5' promoter region of CYP17, with a possible influence on the transcription of CYP17, was determined in two groups of hyperandrogenic patients, namely those with polycystic ovary syndrome (PCO) and those with congenital adrenal hyperplasia compared to a reference population. No significant difference in the prevalence of this polymorphism was found between the populations, nor was there any relationship between the prevalence of a particular allele and androgen levels in patients with PCO implying that this polymorphism is not an important cause of dysregulation of this gene.

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