A monogenic disease or a monogenic disorder is a condition determined by the interaction of a single pair of genes. This is in contrast to a polygenic condition wherein several genes (polygene) are involved. In humans, the monogenic disease is less frequent than the polygenic disease. It is also less complicated than the latter and may follow a pattern based on Mendelian inheritance. Since monogenic disease involves a single pair of genes the dysfunctional or mutated gene may be identified more easily than polygenic disease.
In monogenic disease, a single gene mutation may lead to disease. Monogenic diseases are mostly pediatric disorders. Some of human diseases due to autosomal dominant single-gene defects include familial hypercholesterolemia, polycystic kidney disease, neurofibromatosis type I, hereditary spherocytosis, Marfan syndrome, and Huntington's disease. Examples of autosomal recessive monogenic disorders include sickle cell anaemia, cystic fibrosis, Tay-Sachs disease, phenylketonuria, mucopolysaccharidoses, lysosomal acid lipase deficiency, glycogen storage diseases, and galactosemia. X-linked monogenic disorders are single-gene mutations in the X chromosome. They include hemophilia and Duchenne muscular dystrophy. Y-linked monogenic disorders are associated with single-gene mutations in the Y chromosome and are very rare. They are passed on from men to their sons. Mitochondrial disease is another example of a monogenic disorder and involving mitochondrial DNA, which is passed from the mother to offspring.