HOMOZYGOSITY FOR Hb E-SASKATOON [β22(B4)Glu → Lys] IN A TURKISH PATIENT

Abstract

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 [β22(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 α/β and β^X/β^A-mRNA (X = Hb E-Saskatoon) ratios were determined. Normal α/β and β^X/β^A-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 β-globin mRNA made it possible for rapid diagnosis of Hb E-Saskatoon, and for its differentiation from Hb E [β26(B8)Glu → Lys (GAG → AAG)]. Analysis of the restriction fragment length polymorphism (RFLP) in the β-globin gene complex of the index patient and of another unrelated family with a compound heterozygosity for Hb E-Saskatoon and β-thalassemia revealed that the Hb E-Saskatoon mutation shared a common allele.