Prevalence of alpha-chain variants at birth.

Hemoglobin electrophoresis of cord blood from 4,499 newborns was performed as part of a sickle cell disease detection program. Although the expected frequency of the genes for hemoglobins S and C were observed, six newborns (five kindreds) were heterozygous for an alpha G Hb. In four kindreds, the alpha chain variant was identified as Hb G-Philadelphia. In each case, heterozygosity for this Hb was manifested at birth by the presence of Hb F/G (alpha 2 G gamma 2), a slow Hb migrating between the positions of Hbs S and C on cellulose acetate. In some newborns, Hb G (alpha 2 G beta 2) was also detectable, so that these cord bloods had four hemoglobin components: F, F/G, A, and G. The prevalence of Hb G-Philadelphia in this population sample is higher than that usually reported for black Americans and may represent a founder effect. Comprehensive screening of cord blood hemoglobins should use electrophoresis on alkaline media as the primary testing procedure because it allows recognition of most variants, such as the D (G) hemoglobins. Reliable identification of Hbs S and C requires citrate agar electrophoresis as a confirmatory test.