Some defects are congenital, or present at birth. Klinefelter's Syndrome is a chromosome abnormality where there is an extra X chromosome. This syndrome prevents sperm production. Sertoli's Cell Only Syndrome results in an inability to produce sperm because the cells responsible for sperm production don't develop during fetal development. Undescended Testicles is another cause for sperm production failure.
Testicles develop in the abdomen of the fetus and then descend into the scrotum after birth.
If the testicles fail to descend, and go unnoticed, then the warmth of the body destroys the sperm manufacturing capabilities. Symptoms Klinefelter's Syndrome often goes unnoticed until infertility is apparent. Sertoli's Cell Only Syndrome is only detectable with infertility tests. Semen has all of the normal components except sperm. Undescended Testicles can be detected by physical exam of the scrotal sac.