ABSTRACT
Over 700 different inherited variants of hemoglobin have been described in humans. The development of the polymerase chain reaction has revolutionized prenatal diagnosis. Most of the clinically significant hemoglobinopathies are prenatally diagnosable in this manner, such as Hbs S, C, E, and D Los Angeles. Thalassemias due to deletions, such as a-thalassemia, are diagnosed by either Southern blots or amplifications in which amplification spans the deletion and variants are detected by size fractionation. The adult level of Hb A2 of 2% to 3.5% of the total hemoglobin is not attained until approximately 2 years of age. Several glycosylated hemoglobins accumulate in red cells at a rate proportionate to the concentration of glucose in the blood; measurement of glycosylated hemoglobin provides an estimate of the average blood glucose level over the life span of the red cells, aiding in the regulation of diabetes. Most abnormal hemoglobins are due to amino acid substitutions that change net ionic charge, thereby altering electrophoretic mobilities.
