Title: Human disease - Diseases of genetic origin | Britannica
Headings: Diseases of
genetic
origin

Diseases of genetic origin
Factors relating to genetic injury
Heredity and environment
Chemical and physical injury

Content: Further confusion often arises over the terms genetic and familial. A familial disease is hereditary, passed on from one generation to the next. It resides in a genetic mutation that is transmitted by mother or father (or both) through the gametes to their offspring. Not all genetic disorders are familial, however, because the mutation may arise for the first time during the formation of the gametes or during the early development of the fetus. Such an infant will have some genetic abnormality, though the parents themselves do not. Down syndrome is an example of a genetic disease that is not familial. Factors relating to genetic injury
The causes of mutations are still poorly understood. Certain factors, however, are thought to be important. Maternal age plays an important role in predisposing toward genetic injury. The frequency of Down syndrome and of congenital malformations increases with the age of the mother.