Sickle-cell anemia is the most common inherited disease among black, striking 1 in 500 children born in the United States. The disease is caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells. The abnormal hemoglobin molecules tend to link together and crystallize, especially when the blood oxygen content is lower than normal. This can occur because of high altitudes, overexertion, or reparatory ailments. The problem is aggravated by the blockages which cause oxygen deprivation in other parts of the system and further sickling of cells.
Blood transfusions can relive symptoms, but there is no cure.
These carriers are usually healthy, although some suffer some symptoms of sickle-cell anemia after an extended period of low blood oxygen levels. The high incidence of heterozygotes may be related to the fact that in certain environments, the single copy of the allele imparts an advantage to the individual. In areas where malaria is endemic, heterozygotes have an enhanced resistance to infection with the parasites compared to individuals homozygous for the normal allele. Thus, the high frequency of the sickle-cell trait in American blacks is a vestige of their African heritage. The probability that two carriers for the same rare deleterious allele will meet and mate is relatively low.