Hb Belluno [ß111(G13)Val→Gly;ß133(H11)Val→Val (HBB: c.335T > G;402G > C)]: Incidental Detection of a New Clinically Silent ß Chain Variant During Hb A1c Determination by High Performance Liquid Chromatography.

ABSTRACT

A previously unreported ß chain variant, Hb Belluno [ß111(G13)Val→Gly;ß133(H11)Val→Val (HBB c.335T > G;402G > C)], was incidentally discovered in a woman suffering from diabetes, during glycated hemoglobin (Hb A1c) assay. Its presence was suspected because of a small abnormal peak with a retention time just shorter than that of normal Hb A1c. Standard high performance liquid chromatography (HPLC), capillary zone electrophoresis (CZE) and agarose gel electrophoresis did not allow to separate the variant from Hb A. The reversed phase HPLC of globin chains showed the presence of a heterozygous ß-globin variant amounting to approximately 43.5% of the total ß chains. Later, this variant was found in five other members of the same family and DNA sequencing analysis confirmed a ß-globin gene mutation. The variant is clinically silent in all patients and showed a slight instability with both heat and isopropanol tests. The other three mutations at this locus also affect stability. Hemoglobin (Hb) variants may invalidate the results of Hb A1c analysis and could result in mismanagement of diabetes. A comment alerting the requesting clinician to the presence of the Hb variant must be appended to the Hb A1c result. Additionally, many Hb variants can be chromatographically and/or electrophoretically silent. Therefore, when the clinician suspects a variant Hb, it is not sufficient to get a negative response from an HPLC screening test to rule it out. A dialogue with the pathologist is essential, involving exchange of information and sharing a diagnostic work-up including surveys to assess Hb stability and oxygen affinity, as much as DNA sequencing.