HB-SEAL-ROCK [(ALPHA-2)142-TERM-]GLU, CODON-142 (T)UNDER-BAR-AA-](G)UNDER-BAR-AA] - AN EXTENDED ALPHA-CHAIN VARIANT ASSOCIATED WITH ANEMIA,MICROCYTOSIS, AND ALPHA-THALASSEMIA-2 (-3.7-KB)

Hb Seal Rock was first reported in a young African-American woman and her 2-year-old daughter (1). It is an extended cc chain variant which, like Hb Constant Spring, is present in small quantity and is expresse d as an alpha-thalassemia. The mutation, TAA-->GAA affects codon 142 o f the alpha 2 gene. In this family, the index case was a compound hete rozygote for Hb Seal Rock trait and for alpha-thalassemia trait (-3.7 kb). Her hematologic expression was similar to mild Hb H disease, pres umably because the Seal Rock mutation affects the alpha 2 gene that is normally responsible for approximately 70% of alpha-globin synthesis. Her daughter had only Hb Seal Rock trait, but was phenotypically alph a-thalassemia-2 trait due to the expression of the Seal Rock mutation on one of her alpha 2-globin genes, the other three alpha-globin genes being unaffected.