A Novel β Globin Gene Mutation, Reported As An α Chain Hemoglobin Variant By High Performance Liquid Chromatography (HPLC) & As Sickle Cell Trait On New Born Screening: A case Report

There are 827 variants of β thalassemia reported to the registry of human hemoglobin variants and thalassemias registry ¹. Genetic mutations of β thalassemia are very diverse but can be broadly divided in to non deletion forms and deletion forms. The new mutation is a frame shift insertion in exon 2 of the β globin gene. To the best of our knowledge this mutation has never been described before and presents as a mild form β thalassemia intermedia.

To describe the phenotypic presentation of the new β globin variant, due to insertion of 9 nucleotides (AAAGTGCTC) between nucleotides c.207 and c.208.

A 22 months-old Hispanic boy who was referred for evaluation of persistent anemia. The new born screening for the child was positive for sickle cell trait. Initial hemoglobin (Hb) was 8.8, hematocrit was 27 and MCV was 65.5, which were decreased. RDW was 25.2, which was increased. Hemoglobin evaluation by acid and alkaline electrophoresis and HPLC revealed a HbS 0%, HbF 6.5% HbA 78.4%, HbA₂ 4.9% and a Hb variant 10.2%. The interpretation of the results was an α globin variant suggestive of Hb Montefiore and β thalassemia trait. Alpha thalassemia PCR for the 7 most common deletions in the α globin chain was negative. Subsequent α globin gene sequencing revealed no α globin gene mutations. On physical exam there were no bony changes or hepatosplenomegaly.

Family History

The mother is 29-year-old with HbAA. The father is 39-years-old with the same mutation on beta globin gene analysis. Hb electrophoresis also suggested an α and β globin mutation. Alpha thalassemia PCR was negative and he had a normal α globin gene copy number. At age 19 he had a splenectomy secondary to splenomegaly and hypersplenism. He is consistently anemic with Hb< 9 and MCV < 70.

The child has a paternal half brother, who is 21 years old and has similar problems as father. He had a splenectomy at the age of 17 after admission for abdominal pain. The patient has a 5-year-old sibling, who is normal with HbAA and another paternal half sibling reported as no anemia.

Though β thalassemia intermedia is most commonly homozygous or compound heterozygous, less frequently it can be due to single locus mutation. DNA sequencing of the α globin gene of the index case was completely normal and there was normal copy number of the α globin gene in the father. No Hb S was found on Hb electrophoresis.

The new mutation adds 9 base pairs to exon 2 and 3 amino acids (Lys-Val-Leu) between amino acid 68 and 69 of the protein. This elongates the beta chain which can lead to instability and precipitation of Hb as well as hemolysis and anemia². Further studies like short time incubation and pulse chase globin chain synthesis experiments are needed to know the stability of the β globin protein³. In addition, an increase of α globin gene copy number can also be a reason for increasing the severity of β thalassemia trait². However the α gene copy was normal in the father.

We present a case of a child with a false positive abnormal newborn screen suggestive of sickle cell trait, as well as a Hb electrophoresis suggestive of an alpha globin mutation. As the father and paternal brother have had a splenectomy in their teen years with noted hepatosplenomegaly, suggestive of increased hemolysis, and the anemia is more severe than usual for β thalassemia trait, this suggests that phenotypically the c.199_207dup variant presents as a mild β thalassemia intermedia. In addition, there does not seem to be any bony abnormalities associated with marrow hyperplasia. As both our patients are heterozygous for this novel mutation with normal α globin gene copy number and alpha globin sequencing, we suspect that elongation of the β globin produces an unstable hemoglobin with a mild β thalassemia intermedia phenotype².

References

1. Databases of human hemoglobin variants and other resources at the globin gene server. Hemoglobin. 25(2):183-93, 2001 May.

2. Galanello R, Cao A. Relationship between genotype and phenotype. Thalassemia intermedia. Annals of the New York Academy of Sciences 1998; 850:325-33.

3. Is hemoglobin instability important in the interaction between hemoglobin E and beta thalassemia? Blood September 15, 1998 vol. 92 no. 6 2141-2146.

No relevant conflicts of interest to declare.