The causes of a reduced reproductive function (hypogonadism) may be classified according to the origin of the disease. Pre-testicular factors are due to alterations in the central regulation and the hypothalamic-pituitary-testis axis, while testicular factors (from primitive testicular alterations) manifest themselves as hypergonadotropic hypogonadism and are a major cause of azoospermia and oligozoospermia. When post-testicular factors are present, the reproductive and endocrine functions are normal but there is an obstacle to semen outflow because of occlusions, infections and inflammation of the genital tract. Genetic factors such as karyotype abnormalities, microdeletions of the Y chromosome mutations and polymorphisms are discussed extensively.
Keywords: Anejaculation, Anorchia, Cryptorchidism, Cystic Fibrosis, Endocrine Disruptor, Germinoma, Hypogonadism, Kallmann Syndrome, Klinefelter Syndrome, Laurence-Moon Syndrome, Lowe syndrome, Microdeletions of the Y Chromosome, Obstructive Azoospermia, Papillomavirus, polymorphism, Prader- Willi Syndrome, Retrograde Ejaculation, Robertsonian Translocation, Testicular Dysgenesis, Varicocele.