Genetic disordersare diseases caused by alterations ingenes. When genes are altered, their products can be dysfunctional or not produced at all. For example, in the case of sickle cell anemia, the hemoglobin does not function properly. This causes the red blood cells to be defective and thus destroyed, leading to anemia.

Genetic disorders can be single gene disorders (or单基因疾病), or multifactorial disorders, where more than one gene is involved, and the environment also plays an important role.