Isolated follicle stimulating hormone (FSH) deficiency due to mutations in FSHβ is an extremely rare autosomal recessive disease that has only been reported in ten patients to date. Symptoms of the disease include amenorrhoea and hypogonadism in women and azoospermia and normal testosterone levels in men. This study describes a Chinese male patient who presented with cryptorchidism and infertility. His serum hormonal profile revealed low FSH, elevated LH and normal testosterone levels. Sequence analysis identified a novel homozygous mutation in the FSHβ gene (c.343C > T) predicted to result in a premature termination codon and a truncated FSH protein (p.R115X). Both parents were heterozygous carriers of the mutation with normal pubertal development and fertility. The patient's testicular volume increased after one year of exogenous FSH replacement therapy at which point spermatocytes were detected in seminal samples, indicating potential future spermatogenesis. The expanded spectrum of FSHβ mutations and associated clinical manifestations described in this study may improve the diagnosis and treatment of this disease.
