Hemoglobin South Florida: New Variant With Normal Electrophoretic Pattern Mistaken for Glycosylated Hemoglobin

An 8.75-yr-old Caucasian boy was discovered to have a markedly elevated (14.8%) hemoglobin A_1c(HbA_1c) as estimated by ion-exchange chromatography (Bio Rex 70). Glycohemoglobin (GHb) measured by a colorimetric method with thiobarbituric acid (TBA) was normal (equivalent to a 6.4% HbA_1c). Nondiabetic quantities of GHb were found with affinity chromatography, and the glucose tolerance test was normal. Intensive efforts to identify an abnormal variant hemoglobin by several electrophoretic methods were unsuccessful. A family survey identified a similar abnormality in 11 other individuals, revealing an autosomal-dominant pattern. None of the affected individuals had any other hematologic abnormality. Structural analysis in one family member revealed a new hemoglobin variant (∼45% of the total hemoglobin) with the substitution of methionine for valine at the β-NH₂-terminal. In addition, the initiator methionine residue was preserved. Approximately 20% of the variant hemoglobin was modified by acetylation of the NH₂-terminal methionine. The modified variant coeluted with HbA_1c. We suggest that patients who do not have an explanation for their elevated HbA_1c should have GHb measured by the TBA method or affinity chromatography because hemoglobin electrophoresis does not identify this confounding artifact.