Characterization and Confirmation of Mildly Unstable Hb Pontoise or α1 63(E12) Ala > Asp and Literature Review.

Abstract

Genotype-phenotype correlation and potential genetic risk in the compound heterozygosity for unstable hemoglobins (UHbs) and α⁰-thalassemia were discussed. Capillary electrophoresis and gene sequencing helped to establish the diagnosis. Hematological analysis showed the following findings: MCV 80.6 fL, MCH 27 pg, HGB 133 g/L, RBC 4.93 × 10¹²/L, Hb A: 94%, Hb X: 3.6% (zone 12) and Hb A₂: 2.4%. DNA analysis revealed the patient was a Hb Pontoise carrier (HBA1: c.191C > A). Hb Pontoise resulted from an GCC > GAC substitution at codon 63 of the HBA1 genes, but carriers were usually asymptomatic or with only borderline hematological abnormalities. Due to mild instability of Hb Pontoise, its diagnosis relied on genetic diagnosis. Considering the high frequency of thalassemia in South China, accurate genotyping and appropriate genetic counseling should be performed for unstable hemoglobin carriers.