Delayed Diagnosis of a 17-Hydroxylase/17,20-Lyase Deficient Patient Presenting as a 46,XY Female: A Low Normal Potassium Level Can Be an Alerting Diagnostic Sign

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or combined enzyme deficiencies partially or completely (2). Over 100 mutations in the CYP17A1 gene have been associated with combined 17-OH/17,20-lyase deficiency (OMIM 202110), including point mutations, small insertions or deletions, splice site alterations, and rarely large deletions (1). Isolated 17,20-lyase deficiency is rare and characterized with sex hormone deficiency without mineralocorticoid excess (3). P450 oxidoreductase (POR) and cytochrome b5 Abstract 17-hydroxylase/17,20-lyase deficiency (17-OHD), a rare autosomal recessive defect in adrenal and gonadal steroidogenesis, causes absence of secondary sexual characteristics and frequently associated with hypertension and hypokalemia. Here, we report a 46,XY case who had normal potassium levels and no hypertension. Our patient was a 2.5-year-old female admitted with female external genitalia and inguinal swelling. Pathology of biopsy revealed that this gonad was a testis. Karyotype was 46,XY. She had no hypertension and no hypokalemia. Serum luteinizing hormone and follicle-stimulating hormone levels were high; testosterone, dehydroepiandrosterone sulfate, and androstenedione were low. Human chorionic gonadotrophin stimulation resulted in partial testosterone response. She was initially diagnosed as partial gonadal dysgenesis or testosterone synthesis defect. In her follow-up after noticing low normal potassium levels at age 9 years, progesterone level was measured and detected to be high. Adrenocorticotropic hormone-stimulated steroid measurements were consistent with 17-OHD. Genetic analyses revealed p. R96Q (c.287G>A) homozygous mutation on exon 1 of CYP17A1 gene. In conclusion, evaluation of 46,XY disorder of sex development patients must include serum potassium levels, and near low levels of potassium levels should also suggest 17-OHD despite absence of hypertension or remarkable hypokalemia. Testosterone synthesis defects must be excluded before establishing the diagnosis of partial gonadal dysgenesis.