(4) The most common variants in the United States in order of prevalence are Hb S, Hb C
, Hb E, and Hb D, each the result of a single amino acid substitution in the Hb [beta] chain.
Hb S 8.3% of African Americans Hb E 30% of Southeast Asians Hb C
3% of African Americans Hb D 2% of North Indians and descendants Table 1.
The 4 most common hemoglobin (Hb) variants worldwide and in the US are Hb S, Hb E, Hb C
, and Hb D.
Qualitative disorders, i.e., hemoglobinopathies, result from any of the following: i) substitution of one amino acid for another (as in Hb S and Hb C
); ii) deletion of a portion of the amino acid sequence (as in Hb Gun Hill); iii) abnormal hybridization between two chains during meiosis (as in Hb Lepore); and iv) abnormal elongation of the globin chain (as in Hb Constant Spring).
Among the structural variants, a high gene frequency and significant clinical or hematological effects are observed with Hb S, Hb C
([beta] 6(A3) Glu>Lys) and Hb E ([beta] 26(B8) Glu>Lys).
The SCD family also includes hemoglobinopathies of varying severities in which Hb S is coinherited with Hb C
, Hb D, Hb E, or Hb O (1).
Although most of these variants are of limited clinical significance, many of them, such as homozygous Hb S and Hb C
, produce severe clinical manifestations.
It has been estimated that there are at least 200 000 Americans with diabetes mellitus who also have either Hb C
or S trait (6).
Alkaline electrophoresis is rapid, reproducible, and capable of separating common hemoglobin variants, such as hemoglobin A (Hb A), Hb F, Hb S, and Hb C
, but Hb S, Hb D, Hb G, and Hb Lepore are unresolved from each other, as are Hb C
, Hb [A.sub.2], Hb O-Arab, and Hb E.
Previous studies have shown that some gHb methods yield inaccurate results with samples heterozygous for Hb C
or S (4-7).
At alkaline pH, electrophoretic migration of Hb C
, Hb E, Hb [A.sub.2], and Hb O is similar.
At least 10% of black Americans have either Hb C
or S trait, and there were 19 million black Americans over age 19 in 1990 (7-10).