Human genetic diseases attributable to changes in a single gene include sickle cell anemia, cystic fibrosis, Huntington's disease and fragile X syndrome, explains the World Health Organization. Examples of diseases that are not purely genetic but have a genetic component include cancer, diabetes, asthma and cardiovascular disease.
Sickle cell anemia is a single-gene disorder in which defective haemoglobin molecules cause red blood cells to take on a sickle shape rather than their usual donut shape, states the WHO. These abnormally shaped cells are unable to fit through small blood vessels, resulting in blockages that prevent organs and tissues from receiving adequate amounts of oxygenated blood. The defective cells also have much shorter life spans than normal red blood cells, which results in anemia due to a chronic shortage of red blood cells.
To develop cystic fibrosis, a person must receive a copy of the gene responsible for the disorder from both parents, notes the WHO. People with the disorder have thicker mucus linings in their lungs than usual, placing them at risk for dangerous lung infections. Fragile X syndrome results when there is weak a spot on the long arm of the X chromosome. It is the most common genetic cause of mental retardation. The specific name for the fragile X syndrome gene is the FMR 1 gene.