A rare hemoglobin variant, Hb Belliard

Abstract

There are many documented variants of hemoglobin; however, other than a limited number (such as sickle cell disease), very few are known to have any clinical significance. As advances in detection and identification continue through gel electrophoresis, capillary electrophoresis, and DNA sequencing, more rare variants are identified. Without case reporting, the significance of these variants will remain unknown or continue to be thought of as insignificant. Here we report a rare hemoglobin variant, Hb Belliard, which was detected in a 68-year-old Indian immigrant to the United States. He presented with elevated hemoglobin and was found to have a unique peak on capillary electrophoresis. The specimen was sent for sequencing and was subsequently found to have Hb Belliard. Currently, Hb Belliard is thought to be insignificant.

CASE DESCRIPTION

A 68-year-old Indian man who immigrated from Mumbai, India, to Garland, Texas, in 1980 presented with weakness, fatigue, and morning nausea. His hemoglobin was 17.1 g/dL, and 3 months later it was 17.2 g/dL. A peripheral blood smear revealed significant microcytosis with moderate hypochromasia and a moderate number of target cells. Hemoglobin electrophoresis revealed 83.9% Hb A, 5.6% Hb A2, and 10.5% Hb Bart's or variant (Figure 1a). To further classify the Hb Bart's/variant, the specimen was sent to ARUP Laboratories for gene sequencing and identification. The variant, Lys56Asn, was detected on the HbA1 gene, corresponding to the Hb Belliard variant. Additional testing also found that the patient had a JAK2 mutation and β⁰ thalassemia.

Figure 1.

Hemoglobin electrophoresis: (a) test for the patient described here; (b) a more typical result.

DISCUSSION

Hemoglobin is a tetrameric protein that is predominantly composed of HbA (2 α and 2 β chains) (Figure 1b). Most mutations are caused by a point mutation that substitutes one amino acid for another in one of the globins. The majority of hemoglobin variants occur in the beta globin chains (such as sickle mutation); however, some mutations are known to occur in the alpha chains (such as Hb Belliard). Over 80 diseases have been identified that are due to substitutions that result in changes to the structure of the hemoglobin; some alter function and others are silent (1, 2). As each mutation was discovered, it was assigned a letter as its designation. As more mutations at the same position were identified, nomenclature started to include the name of the city where it was discovered (2, 3). In the modern laboratory, capillary electrophoresis has replaced traditional gel electrophoresis due to its much higher resolution, producing faster, more accurate results. As more mutations are elucidated, it becomes increasingly difficult to identify them, and more sophisticated ways of differentiating the mutations are required. Thus, high-pressure liquid chromatography, isoelectric focusing, hemoglobin DNA sequencing, mass spectrometry, and matrix-assisted laser desorption/ionization–time of flight (MALDI-TOF) are now used to differentiate rare mutations not detected by conventional methods, as in this case (3).

The only other documented case report of Hb Belliard was published in Hemoglobin (1989) as part of a study to find hemoglobin disorders within at-risk populations in Brussels (4). An asymptomatic 20-year-old man of Spanish origin involved in the study was found to have an incidental alpha chain that eluted faster than normal and comprised approximately 25% of the total hemolysate. The abnormality detected was Lys56Asn and was named after a street (Belliard) in Brussels. To further investigate the possible inheritance pattern, his father and brother were also tested and found to have the same mutation. Other mutations at this same position include Hb Thialand (Lys56Thr) and Hb Shaare Zedek (Lys56Glu) (4).

Many variants of hemoglobin do not have known clinical significance; however, with future advances in medicine and more sophisticated detection of physiologic derangements, this may not be true. More consistent case reporting may aid in better understanding of these variants and identification of new clinical importance.