- Azoospermic men with deletion of the DAZ gene cluster are capable of completing spermatogenesis: fertilization, normal embryonic development and pregnancy occur when retrieved testicular spermatozoa are used for intracytoplasmic sperm injection. Mulhall, J.P., Reijo, R., Alagappan, R., Brown, L., Page, D., Carson, R., Oates, R.D. Hum. Reprod. (1997)