Isolated follicle-stimulating hormone (FSH) deficiency in two infertile men without FSH β gene mutation: case report and literature review

Abstract Objective: Congenital FSH deficiency is an exceptional cause of male infertility most often attributed to FSH β gene mutations. The few published cases report azoospermia, severe testicular hypotrophy and normal testosterone levels associated with normal virilization. We report the exploration of two young men aged 26 and 27 years with severe sperm abnormalities, moderate testicular hypotrophy and isolated FSH deficiency. Methods: Several FSH, LH, total testosterone and inhibin B assays and FSH β gene sequencing were performed. Results: FSH was almost undetectable at baseline and poorly responsive to GnRH test, whereas LH was normal at baseline and elevated after GnRH test. Testosterone levels were within the adult range, while inhibin B levels were upper-normal to high. No FSH β gene mutations were found. Exogenous FSH treatment was followed by spontaneous pregnancy in one case and intra-cytoplasmic sperm injection (ICSI) in the other. Conclusions: The paradoxical high levels of inhibin B reflect the presence of functional Sertoli cells and may explain the isolated FSH deficiency. An intra-gonadal factor stimulating inhibin B secretion is discussed.