A novel homozygous loss-of-function mutation in RAD51AP2 induces male infertility with nonobstructive azoospermia.

similar phenotype in the proband’s brother, who had a 9-year history of male infertility. The proband did not have a medical history of infectious disease, chronic disease, or cancer or a history of smoking or consuming alcohol. He had normal sexual activity with ejaculation. The physical examination showed normal development of the penis, prostate, epididymis, and vas deferens. No varicocele was observed, but bilateral testicular size (10 ml) was slightly smaller than reference value (>12.5 ml) 2 . Further laboratory examinations showed a normal karyotype and normal serum levels of hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T). There was no microdeletion in the Y chromosome. However, semen samples from the proband and his brother lacked sperm before and after centrifugation. Their testicular biopsies showed many spermatocytes but no spermatids or