Alpha-thalassemia is a prevalent blood disorder found in tropical and subtropical regions worldwide, posing a significant public health burden. In regions like Southeast Asia and the Mediterranean, this condition can manifest in different forms, ranging from mild to severe anemia (hemoglobin H (HbH) diseases) or even lethal outcomes (Hb Bart’s hydrops fetalis).
In normal individuals, there are four alpha-globin genes, two on each chromosome 16 pair (αα/αα). Alpha thalassemia trait phenotype occurs due to deletions of two alpha-genes, either in the cis type (αα/–) on the same chromosome or the trans type (α-/α-). Hb Bart’s hydrops fetalis results from the deletion/inactivation of all four α-globin genes (–/–) while HbH disease is mainly caused by the deletion/inactivation of three α-globin genes (–/-α).
Common Alpha-Thalassemia Variants:
Among the various alpha-thalassemia gene deletions, the -α3.7 and -α4.2 single gene deletions are the most prevalent. Additionally, double gene deletions in cis, such as — SEA, — FIL, and –THAI alleles, are commonly observed in Southeast Asia. On the other hand, the –MED and –(α)20.5 double-gene deletions are more frequent in the Mediterranean area. Understanding the prevalence of these genetic variations is crucial for developing a comprehensive protocol for managing six common types of alpha thalassemia in the Southeast Asia and Mediterranean regions.
Alpha thalassemia phenotype and genotype:
| Phenotype | Genotype |
| Haemoglobin Bart hydrops fetalis (Hb Bart) syndromes | Deletion/inactivation of all four α-globin genes (–/–) |
| Haemoglobin H (HbH) disease | Deletion/inactivation of three α-globin genes (–/-α) |
| α-thalassemia trait/carrier | Deletion/inactivation of two α-globin genes either in cis (–/αα, or α0 carrier) or in trans (-α/-α or α+) |
| α-thalassemia silent carrier | Deletion/inactivation of one α-gene (-α/αα or α+ carrier) |
Alpha-thalassemia is a widespread blood disorder with significant variations in its prevalence and genetic makeup in different regions. In Southeast Asia and the Mediterranean, understanding the specific genetic variants responsible for this condition is essential for effective management and treatment. By developing a comprehensive protocol for these regions, we can improve the healthcare outcomes for individuals affected by alpha-thalassemia.
