To the Editor.—
In their excellent discussion of "Genetic Diversity in Hemoglobins: Disease and Nondisease" (239:2681, 1978), Scott and Gilbert comment on the gene prevalence for several common autosomal recessive hematologic and nonhematologic disorders. However, they do not make it clear whether they are talking about gene frequency or the proportion of heterozygotes (carriers) for that particular gene in the population. By the Hardy-Weinberg equation, the heterozygote proportion is approximately twice the gene frequency.1Thus, the figure of 5% to 6% given by Scott and Gilbert for cystic fibrosis really represents the carrier rate in the white population of the United States, while the gene frequency is half that, or 2.5% to 3% (1/40 to 1/33). Multiplying the gene frequency by itself would give the generally accepted incidence of 1/1,600 to 1/1,089 for newborns with cystic fibrosis (homozygotes).Similarly, the figures given for phenylketonuria in the general population (2%)
Bass HN. Genetic Diversity in Hemoglobins. JAMA. 1978;240(21):2249. doi:10.1001/jama.1978.03290210031015
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