Alpha Thalassemia Trait Incidence in Southeast Asia
Alpha thalassemia trait is highly prevalent in Southeast Asia, with gene frequencies reaching 30-40% in certain populations, making it one of the most common genetic disorders in this region. 1
Regional Prevalence Data
The incidence of alpha thalassemia trait varies significantly across Southeast Asian populations:
- Northern Thailand and Laos demonstrate the highest carrier rates, with alpha-thalassemia gene frequencies reaching 30-40% 1
- Hemoglobin Constant Spring, a non-deletional alpha thalassemia variant particularly common in Southeast Asia, occurs with gene frequencies between 1-8% 1
- Alpha thalassemia is the most common cause of non-immune hydrops fetalis in Southeast Asia, accounting for 28-55% of cases 2
Clinical Significance in Southeast Asia
Alpha thalassemia represents probably the most common monogenic gene disorder worldwide and is especially frequent in Southeast Asia. 3 The high prevalence creates several important clinical considerations:
- Homozygous alpha-0 thalassemia (--/--) is a serious health problem in Southeast Asia and the Philippines, responsible for the majority of hydrops fetalis cases in this region 4
- The interaction of alpha thalassemia with other hemoglobinopathies (such as Hemoglobin E, which reaches 50-60% frequency at the Thailand-Laos-Cambodia junction) leads to over 60 different thalassemia syndromes 1
- Hemoglobin Bart's hydrops fetalis (the lethal form with no alpha-globin synthesis) occurs when both parents carry alpha-0 thalassemia deletions 3
Geographic Distribution Pattern
Alpha thalassemia shows distinct geographic clustering:
- The disorder is particularly prevalent in tropical and subtropical regions, with Southeast Asia representing the epicenter of alpha-0 thalassemia deletions 3, 4
- Mediterranean countries, Africa, the Middle East, and the Indian subcontinent also show high prevalence, though alpha-0 deletions are less common outside Southeast Asia 3
- North American and North European countries have seen increasing incidence due to demographic changes and immigration from endemic areas 3
Screening Implications
Given the high carrier frequency in Southeast Asia, population-based screening strategies are essential:
- Asians comprise 10% of all California births and represent the population at highest risk for alpha-0 thalassemia in the United States 4
- Carrier screening should target individuals of Southeast Asian descent, as both parents must be carriers for severe disease to occur 2, 1
- When both parents carry alpha thalassemia trait, there is a 25% risk with each pregnancy of having a child with severe disease 2