To the Editor.—
The article by Drs Wilfond and Fost1 on the cystic fibrosis gene confines itself to the medical and social implications for heterozygote detection. The reliable detection of heterozygotes has important theoretical implications for the science of medical genetics: it will allow the testing of the hypothesis of increased heterozygote fitness for common lethal autosomal recessive diseases.
Presumably, the commonness of certain genetic diseases such as sickle cell anemia and cystic fibrosis (CF) is caused by the increased reproductive fitness of heterozygotes over that of noncarriers. The increased resistance of sickle cell heterozygotes to malaria is the paradigm for such balanced polymorphisms.
About one in 21 whites is a carrier for the genetically lethal disease of CF. If we assume that the fitness of heterozygotes over that of noncarriers is small, then only when selective pressures are great (like that of falciparum malaria in tropical Africa) could
. . . [Full Text PDF of this Article]
