Epidemiology of HbE and Thalassemia Traits in Southeast Asia
SE Asia is the third most populous region in the world [11], encompassing 10 countries with more than 650 million people inhabiting an area over 4.5 million km2. SE Asia is a genetic cauldron of different ethnicities descending from diverse and complex origins [11,12]. Shaped by local malarial environmental pressures, SE Asia’s common genetic denominator is thalassemia, presenting with over 60 different allelic variants, but mainly dominated by 4 major thalassemic syndromes [13]. The α-thalassemias, with a gene prevalence approaching 40% in northern Thailand and Laos, are considerably less common in Malaysia and the Philippines (around 5%) [13]. The β-thalassemias showing local variations in genetic prevalence account for up to 9% of all cases. Thirdly, Hb Constant Spring [CS] is also seen, with gene frequencies of up to 8% [13]. HbE, the thalassemic symbol of SE Asia, is increasingly encountered worldwide. HbE gene prevalence may reach up to 70% locally in northeastern Thailand and and up to 62% at the triple border region between Thailand, Cambodia, and Laos [13–15]. Apart from SE Asia, thalassemia genes (including HbE) are also present with diminishing gene frequency in Yunnan, Nepal, Northeastern India, Pakistan, Sri Lanka, Bangladesh, Hong Kong, and Taiwan [13–24].