Indirect evaluation of a gene frequency: calculation of beta-thalassemia frequency in Algeria based on associated hemoglobin variants frequency.

The gene frequency (q) of beta-thalassemia (T) is more difficult to evaluate directly than the frequency of hemoglobin variants (V), Hb S and Hb C being the most frequent ones in Algeria. Among 150 subjects with a phenotype V, we identified 76 compound heterozygotes VT(0) (T(0) = beta(0)-thalassemia) and 74 homozygotes VV: qT(0) is therefore practically equal to qV. Calculation based on the investigation of 54 subjects detected during the same period (33 VT among which 23 VT(0) and 21 TT among which 9 T(0) T(0) yields qT = 1.43 qT(0) = 1.43 qV. According to Cabannes [1965], qV is equal to 0.0113, qT is 1.43 X 0.0113 = 0.0162. This indirect method, based on investigation of patients, gives a less precise evaluation of gene frequency than a direct method based on large population screening. This evaluation, however, is sufficient to estimate the incidence of beta-thalassemia and its impact from a public health point of view.