Genetic Disease, Human

human genetic disease, any of the diseases and disorders that are caused by mutations in one or more genes.

With the increasing ability to control infectious and nutritional diseases in developed countries, there has come the realization that genetic diseases are a major cause of disability, death, and human tragedy. Rare, indeed, is the family that is entirely free of any known genetic disorder. Many thousands of different genetic disorders with defined clinical symptoms have been identified. Of the 3 to 6 percent of newborns with a recognized birth defect, at least half involve a predominantly genetic contribution. Furthermore, genetic defects are the major known cause of pregnancy loss in developed nations, and almost half of all spontaneous abortions (miscarriages) involve a chromosomally abnormal fetus. About 30 percent of all postnatal infant mortality in developed countries is due to genetic disease; 30 percent of pediatric and 10 percent of adult hospital admissions can be traced to a predominantly genetic cause. Finally, medical investigators estimate that genetic defects—however minor—are present in at least 10 percent of all adults. Thus, these are not rare events.

A congenital defect is any biochemical, functional, or structural abnormality that originates prior to or shortly after birth. It must be emphasized that birth defects do not all have the same basis, and it is even possible for apparently identical defects in different individuals to reflect different underlying causes. Though the genetic and biochemical bases for most recognized defects are still uncertain, it is evident that many of these disorders result from a combination of genetic and environmental factors.

This article surveys the main categories of genetic disease, focusing on the types of genetic mutations that give rise to them, the risks associated with exposure to certain environmental agents, and the course of managing genetic disease through counseling, diagnosis, and treatment. For full explanation of Mendelian and non-Mendelian genetics, genetic mutation and regulation, and other principles underlying genetic disease, see the article heredity. The genetics of tumour development, briefly explained in this article, are covered at length in the article cancer.