A 30-year-old female who is homozygous for a Hb E-like abnormal
hemoglobin and her immediate relatives were studied. Clinical examination of the proband revealed no abnormality. Routine hematological analysis showed that her
hemoglobin level was 12 g/dL, MCV 82 fL, MCH 28 pg, RDW 15%. DNA sequence analysis indicated the presence of a G-->A substitution at
codon 22 corresponding to an abnormal
hemoglobin, namely
Hb E-Saskatoon [beta22(B4)Glu-->Lys (GAA-->AAA)]. Absence of any abnormalities in clinical and routine hematological investigations of the homozygous patient indicated that the phenotypical expression of the
Hb E-Saskatoon is very mild. Using a reverse transcription-polymerase chain reaction technique, the alpha/beta and betaX/betaA-
mRNA (X =
Hb E-Saskatoon) ratios were determined. Normal alpha/beta and betaX/betaA-
mRNA ratios were found in the homozygous patient and in all heterozygotes, indicating that the respective mutation did not alter the stability of the
mRNA. FokI restriction
enzyme analysis of the polymerase chain reaction products obtained from the genomic
DNA and/or
beta-globin mRNA made it possible for rapid diagnosis of
Hb E-Saskatoon, and for its differentiation from Hb E [beta26(B8)Glu-->Lys (GAG-->AAG)]. Analysis of the restriction fragment length polymorphism (RFLP) in the
beta-globin gene complex of the index patient and of another unrelated family with a compound heterozygosity for
Hb E-Saskatoon and
beta-thalassemia revealed that the
Hb E-Saskatoon mutation shared a common allele.