Association of Hb Thailand [α56(E5)Lys→Thr] and Hb Phnom Penh [α117(GH5)-Ile-α118(H1)] with α(0)-thalassemia: molecular and hematological features and differential diagnosis.

We report the molecular and hematological characteristics of two rare hemoglobin (Hb) variants found in associations with a common α(0)-thalassemia (α(0)-thal) in Thai patients. The first case (P1) was a generally healthy 27-year-old man discovered during our ongoing thalassemia screening program. Hemoglobin and DNA analyses identified a previously undescribed condition of compound heterozygosity for Hb Thailand [α56(E5)Lys→Thr] and α(0)-thal (SEA deletion). The second case (P2) was a 4-year-old boy with hypochromic microcytic anemia. Hemoglobin and DNA analyses also identified a compound heterozygosity for Hb Phnom Penh [α117(GH5)-Ile-α118(H1)] in association with α(0)-thal (SEA deletion). Although Hb H (β(4)) inclusion bodies were observed in both cases, Hb analysis using both high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) did not show Hb H. While the two Hb variants could be recognized on Hb HPLC analysis, their corresponding Hb A(2) derivatives: the Hb A(2)-Thailand and Hb A(2)-Phnom Penh, were clearly observed on CE. Apparently, combination of these two Hb variants with α(0)-thal are not expressed as Hb H disease. The two Hb variants could be confirmed by polymerase chain restriction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific PCR assays.