[Clinical and genetic analysis of a patient with isolated 17,20 lyase deficiency presenting with pubertal gynecomastia].

To explore the clinical and genetic basis for a patient with isolated 17,20 lyase deficiency presenting with pubertal gynecomastia.Clinical manifestation, steroid analysis as well as genetic testing were carried out for a 14-year-old boy featuring puberty gynecomastia.The patient was admitted due to puberty gynecomastia for 2 years. Physical examination showed Tanner B5, G2 and normal blood pressure. Laboratory examination showed normal range of serum potassium and blood gas. Steroid analysis revealed extremely high pregnenolone, progesterone, 17-hydropregnenolone and 17-hydroprogesterone, Correspondingly, the DHEA, androstenedione, testosterone and dihydrotestosterone were low. He was found to harbor compound heterozygous variants of CYP17A1 gene (c.1304T>C/p.F435S and c.1346G>A/p.R449H), among which the R449H variant may result in isolated 17,20 lyase deficiency by altering the structure of redox-partner binding site.Isolated 17,20 lyase is a rare cause for puberty gynecomastia. The p.R449H variant of the CYP17A1 gene can result in isolated 17,20 lyase deficiency.