Sickle-cell disease (SCD), or sickle-cell anaemia (SCA) or drepanocytosis, is an autosomal recessive genetic blood disorder with overdominance, characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various complications. The sickling occurs because of a mutation in the hemoglobin gene. Life expectancy is shortened. In 1994, in the US, the average life expectancy of persons with this condition was estimated to be 42 years in males and 48 years in females, but today, thanks to better management of the disease, patients can live into their 50s or beyond. Sickle-cell disease occurs more commonly in people (or their descendants) from parts of tropical and sub-tropical sub-saharan regions where malaria is or was common. In areas where malaria is common, there is a fitness benefit in carrying only a single sickle-cell gene (sickle cell trait).
Contributions by Jfdwolff, Diberri, and Samuel Blanning.