Secondary polycythaemia in a Malay girl with homozygous Hb Tak

ABSTRACT

Hb Tak is one of more than 200 high affinity haemoglobin variants reported worldwide. It resultsfrom the insertion of two nucleotides (AC) at the termination codon, between codon 146 and codon147 of the beta-globin gene [Beta 147 (+AC)]. Polycythaemia is the main clinical feature althoughaffected carriers are usually asymptomatic and do not require intervention. Several case studies inthis region have reported the co-inheritance of Hb Tak with Hb E, delta beta and beta thalassaemiawith one case of homozygous Hb Tak in a Thai boy. In this case report, a cluster of haemoglobinTak was found in a family of Malay ethnic origin. Cascade family screening was conducted whileinvestigating a 4-year old girl who presented with symptomatic polycythaemia. She had 2 previousHb analysis done, at 7-month and 2-year-old with the diagnosis of possible Hb Q Thailand andHomozygous 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 consanguineouslymarried and later diagnosed as asymptomatic carriers of Hb Tak. Consequently, re-analysis of thegirl’s blood sample revealed a homozygous state of Hb Tak. In conclusion, high oxygen affinityhaemoglobin like Hb Tak should be considered in the investigation of polycythaemic patients withabnormal Hb analyses. In this case, DNA analysis was crucial in determining the correct diagnosis.