Hb Oita [alpha45(CE3)His-->Pro]: a new silent hemoglobin variant

Interference of hemoglobin variants in HbA1c quantification

Fasting blood glucose and glycated hemoglobin (HbA_1c) are routine biomarkers to screen and monitor diabetes mellitus. HbA_1c results from glycation at the N-terminus of the β globin chain of tetrameric human hemoglobin. Fasting blood glucose level varies with the nature and amount of food intake, physical exercise, etc., and, accordingly, is a short-term measure of glucose control. In contrast, HbA_1c provides an average measure of glucose control for the long-term (8-12 weeks). Unfortunately, genetic variants of hemoglobin may interfere with HbA_1c quantification using ion exchange chromatography, capillary electrophoresis, immunoassay and boronate affinity chromatography. Mass spectrometry, however, measures total glycation of hemoglobin across both α and β globin chains and correlates well with the ion exchange based method. Additionally, mass spectrometry based quantification is not impacted by the presence of genetic variants of hemoglobin and thus might be a better analytical choice for diabetes mellitus.

Hb Tsukumi [beta117(G19)His-->Tyr]: a new hemoglobin variant found in a Japanese male

We accidentally observed an abnormal elution pattern on high performance liquid chromatogram when we examined the Hb A1c level in a 65-year-old male patient who suffered from pneumoconiosis and alcoholic liver injury. The value of the glycated fraction was within the normal range but the elution patterns on high performance liquid chromatography varied with the glycohemoglobin analyzers. Isoelectrofocusing and urea-cellulose column chromatography showed an anomalous fast-moving beta chain estimated at approximately 47%. The instability test of the hemolysate was slightly positive. Structural analysis demonstrated that the mutant was consisted by a substitution of His-Tyr at beta117. This new variant was named Hb Tsukumi for the place of residence of the patient. Additionally, the nucleotide sequence showed a change of C-->T [CAC (His)-->TAC (Tyr)] at the first base in the 117th codon of the beta gene.