Deficiency of 17,20-lyase causing giant ovarian cysts in a girl and a female phenotype in her 46,XY sister: case report.

A 13-year-old girl was referred because of progressive abdominal pain caused by ovarian torsion and giant ovarian cysts. Secondary sexual characteristics were absent. Hormone analysis revealed markedly elevated serum levels of progesterone and 17-hydroxyprogesterone in combination with very low peripheral concentrations of C19 steroids (dehydroepiandrosterone and androstenedione) and estrogens. Serum concentrations of FSH and LH exceeded the upper limit of normal levels in adult women. The patient's 16-year-old 46,XY sibling showed a female phenotype with similar hormonal disturbances. Both siblings were found to be compound heterozygotes for two mutations in the CYP17 gene: an R347C mutation in one allele and a 25-base pair deletion in exon 1 in the other. The resulting block in 17,20-lyase activity caused an inability to synthesize androgens and estrogens, and increased levels of gonadotrophins due to a lack of negative feedback. The increased levels of gonadotrophins most likely stimulated growth of the ovarian cysts. The administration of a GnRH antagonist reduced the size of the cysts within a few weeks. At present, the girl is being treated with a combination of a GnRH agonist and hormone replacement therapy.