Any disorder caused, partly or wholly, by one or more faults in a person’s DNA. Genetic disorders can be congenital (present at birth) or may become apparent later in life. Most of them are familial (shared by people in the same family). A child can, however, be born with a genetic disorder when there is not any previous family history.
A genetic disorder can arise in two different ways: one or both parents have a defect in their own genetic material that is then inherited by the child, or a mutation arises during the formation of the sperm or ovum cell.
The disorders fall into three broad categories: chromosomal abnormalities, multifactorial defects, and single gene (unifactorial) defects. Chromosomal abnormalities involving a child having an abnormal number of whole chromosomes, or missing bits or extra chromosomes. Single gene defects are created by one abnormal gene or pair of genes. Multifactorial disorders are due to the effects of various genes, often combined with environmental influences or lifestyle influences.