The genetic basis of infertility.

Infertility is defined as the inability to conceive after one year of regular unprotected intercourse; approximately one in six couples wishing to start a family fall into this category. Although, in many cases, the diagnosis is simply 'unexplained', a variety of reasons including lack of ovulation, mechanical stoppage, sperm deficiencies and parental age have been implicated. It is difficult to assess accurately the overall magnitude of the contribution of genetics to infertility as most, if not all, conditions are likely to have a genetic component, for example susceptibility to infection. Nevertheless, a significant number of infertility phenotypes have been associated with specific genetic anomalies. The genetic causes of infertility are varied and include chromosomal abnormalities, single gene disorders and phenotypes with multifactorial inheritance. Some genetic factors influence males specifically, whereas others affect both males and females. For example, chromosome translocations affect both males and females, whereas Klinefelter syndrome and the subsequent infertility phenotype caused by it are specific to males. This article reviews current research in the genetic basis of infertility; gender-specific disorders and those affecting both sexes are considered.