Genetic disorder
About 65% of people have some kind of health problem as a result of congenital genetic mutations. About 1 in 21 people are affected by a genetic disorder classified as "rare" (less than 1 in 2,000 people). Most genetic disorders are rare in themselves. They may affect one person in every several thousands or even millions. Sometimes they are relatively frequent in a population. If they are frequent, it suggests these recessive gene disorders give an advantage in certain environments when only one copy of the gene is present. Sickle cell anaemia is an example of this.