A genetic disease is one caused by damage to one or more genes.
Genetic diseases can be transmitted to the offspring of the affected person (vertical transmission).
There are monogenic disorders which are caused by malfunction of a specific gene. Some of these are due to a dominant allele and are therefore seen in all of the offspring of an affected person. Others are associated with a recessive allele from one parent and can be transmitted to the offspring but symptoms do not develop as the "healthy" allele is carried by the chromosome from the other parent. Furthermore, some genetic diseases only present from a certain age. Advances in molecular biology have made screening tests possible for some genetic diseases. These are particularly performed for pre-implantation diagnosis during in vitro fertilisation or by amniocentesis.
It is sometimes possible to treat genetic defects with an appropriate diet. Gene therapy to treat this type of disease is a future hope.