Secondary polycythaemia in a Malay girl with homozygous Hb Tak

Hb Tak is one of more than 200 high affinity haemoglobin variants reported worldwide. It results from the insertion of two nucleotides (AC) at the termination codon, between codon 146 and codon 147 of the beta-globin gene [Beta 147 (+AC)]. Polycythaemia is the main clinical feature although affected carriers are usually asymptomatic and do not require intervention. Several case studies in this region have reported the co-inheritance of Hb Tak with Hb E, delta beta and beta thalassaemia with one case of homozygous Hb Tak in a Thai boy. In this case report, a cluster of haemoglobin Tak was found in a family of Malay ethnic origin. Cascade family screening was conducted while investigating a 4-year old girl who presented with symptomatic polycythaemia. She had 2 previous Hb analysis done, at 7-month and 2-year-old with the diagnosis of possible Hb Q Thailand and Homozygous Hb D, respectively. Both diagnosis did not fit her clinical presentations. She was plethoric, had reduced exercise tolerance as well as cardiomyopathy. Her parents were consanguineously married and later diagnosed as asymptomatic carriers of Hb Tak. Consequently, re-analysis of the girl's blood sample revealed a homozygous state of Hb Tak. In conclusion, high oxygen affinity haemoglobin like Hb Tak should be considered in the investigation of polycythaemic patients with abnormal Hb analyses. In this case, DNA analysis was crucial in determining the correct diagnosis.