In medicine, the establishment of a detailed family history of any genetic disorders for individuals who are at risk of developing them, or concerned that they may pass them on to their children, and discussion as to likely incidence and available options. Prenatal diagnosis may be available to those at risk of having a child affected by a particular disorder. Genetic counselling of individuals at risk of developing a genetic disorder in adult life can result in the individual taking action to prevent the disorder developing; for example, removal of the ovaries in women at high risk of developing ovarian cancer.
There is a great deal of variation in the mode of inheritance of genetic disorders. Some disorders, such as Huntington's chorea, are inherited as dominant genes and there is a 50% chance of the children of an affected person and a normal person being affected by the disorder. Other disorders, such as cystic fibrosis, are inherited as recessive genes. The possession of a recessive gene does not result in overt disease but the children of an affected person and a normal person have a 25% chance of being affected by the disorder. Other genetic diseases, such as haemophilia, are linked to the X chromosome. These diseases are only found in male children but female children can carry the gene. Other diseases, such as diabetes, schizophrenia, and some forms of cancer have complex genetic and environmental components and risk can be determined from population studies.
Genes associated with some genetic disorders have been isolated in recent years. These have resulted in the development of tests for certain disorders in which inheritance is important, such as Alzheimer's disease and certain forms of breast cancer. After receiving genetic counselling, individuals at risk can be tested to determine if they are likely to develop such diseases later in life.
In the UK, regional centres for genetic counselling have been established and individuals can be referred to them by their general practitioner or by other medical specialists.
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In medicine, the determination of the genetic make-up of an individual to determine if he or she is at risk of developing a hereditary disease later