but others do not, referred to as mosaic Klinefelter syndrome. The reduction of testosterone in the male body normally results in an overall decrease in the production of viable sperm for these individuals thereby forcing them to turn to fertility treatments to father children. Y chromosome deletions Y chromosomal infertility is a direct cause of male infertility due to its effects on sperm production, occurring in approximately one in 2000 males. Usually, affected men show no symptoms, although they may have smaller testes. Men with this condition may exhibit azoospermia (no sperm production), oligozoospermia (small number of sperm production), or they may produce abnormally shaped sperm (teratozoospermia). This case of infertility occurs during the development of gametes in the male. Where a normal healthy male will have both an X and a Y chromosome, affected males have genetic deletions in the Y chromosome. These deletions affect protein production that is vital for spermatogenesis. Studies have shown that this is an inherited trait; if a male is fathered by a man who also exhibited Y chromosome deletions then this trait will be passed down. These individuals are thereby "Y-linked". Daughters are not affected and cannot be carriers due to their lack of a Y chromosome. Other Age group 12–49 (Paternal age effect) Aneuploidy, an abnormal number of chromosomes Centriole Neoplasm, e.g. seminoma Idiopathic failure Cryptorchidism Trauma Hydrocele, particularly hydrocele testis Hypopituitarism in adults, and hypopituitarism untreated in children (resulting in growth hormone deficiency and proportionate dwarfism.) Mumps Malaria Testicular cancer Defects in USP26 in some cases Acrosomal defects affecting egg penetration Idiopathic oligospermia – unexplained sperm deficiencies account for 30% of male infertility. Pre-testicular causes Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including: Varicocele Varicocele is a condition of swollen testicle veins. It is present in 15% of normal men and in about 40% of infertile men. It is present in up to 35% of cases of primary infertility and 69–81% of secondary infertility. Hypogonadotropic hypogonadism due to various causes Obesity increases the risk of hypogonadotropic hypogonadism. Animal models indicate that obesity causes leptin insensitivity in the hypothalamus, leading to decreased Kiss1 expression, which, in turn, alters the release of gonadotropin-releasing hormone (GnRH). Undiagnosed and untreated coeliac disease (CD). Coeliac men may have reversible infertility. Nevertheless, CD can present with several non-gastrointestinal symptoms that can