A laboratory strategy for genotyping haemoglobin H disease in the Chinese

Abstract

Background: The thalassaemias are the commonest blood disorders worldwide, with South East Asia and southern China as areas of high prevalence. Accurate diagnosis of these disorders helps in clinical management with improved outcome.

Methods: The α-globin genotypes of 100 Chinese patients in Hong Kong with haemoglobin H (Hb H) disease were characterised. Single-tube multiplex gap-PCR was used to detect −−^SEA, −α^3.7 and −α^4.2, while Hb CS, Hb QS and codon 30 (ΔGAG) were identified by single-tube multiplex amplification refractory mutation system (ARMS). Automated direct nucleotide sequencing of the amplified α2- and α1-globin genes was performed to characterise other non-deletional α-thalassaemia determinants.

Results: In the 100 cases studied, 99 cases had −−^SEA in combination with deletional α⁺-thalassaemia or non-deletional α-globin gene mutation involving the α2-globin gene. In 70 cases of the deletional form, 43 cases showed the genotype of (−−^SEA/−α^3.7) and 27 cases of (−−^SEA/−α^4.2). Three of the 27 cases of (−−^SEA/−α^4.2) were found to have Hb Q-Thailand linked in-cis with −α^4.2. The remaining 30 cases were of non-deletional form with the following genotypes: 11 cases of (−−^SEA/α^HbCSα), 9 cases of (−−^SEA/α^HbQSα), 3 cases of (−−^SEA/α^{cd30 (ΔGAG)}α), 3 cases of (−−^SEA/α^cd31α), 2 cases of (−−^SEA/α^poly-Aα), 1 case of (−−^SEA/α^HbWestmeadα) and 1 case of (−−^non-SEA/α^HbQSα).

Conclusions: Based on two rapid diagnostic tests, multiplex gap-PCR and multiplex ARMS, more than 90% of the cases were genetically characterised. This laboratory strategy should be widely applicable for genetic diagnosis of α-thalassaemia.