HB Seal Rock [(α2)142 Term→glu, Codon 142 TAA→GAA]: An Extended α Chain Variant Associated with Anemia, Microcytosis, and α-Thalassemia-2 (-3.7 KB)

Abstract

Hb Seal Rock was first reported in a young African-American woman and her 2-year-old daughter (1). It is an extended α chain variant which, like Hb Constant Spring, is present in small quantity and is expressed as an α thalassemia. The mutation, TAA→GAA affects codon 142 of the α2 gene. In this family, the index case was a compound heterozygote for Hb Seal Rock trait and for α-thalassemia trait(-3.7 kb).

Her hematologic expression was similar to mild Hb H disease, presumably because the Seal Rock mutation affects the α2 gene that is normally responsible for approximately 70% of α-globin synthesis. Her daughter had only Hb Seal Rock trait, but was phenotypically α-thalassemia-2 trait due to the expression of the Seal Rock mutation on one of her α2-globin genes, the other three α-globin genes being unaffected.