Homozygous haemoglobin constant spring: A need for revision of concept

Summary Twenty-two patients with mild haemolytic anaemia and haemoglobin (Hb) Constant Spring (CS) of around 6% were studied because they were suspected of having homozygous Hb CS. Family studies revealed Hb CS trait in both parents of eight patients, supporting that they were homozygous for Hb CS. The other patients were included because they had clinical and haematological features similar to the diagnosed cases of homozygous Hb CS. Heterozygosity and homozygosity for Hb CS are clearly distinguishable in that the former is asymptomatic but the latter is associated with overt haemolytic anaemia, and the levels of Hb CS in the two conditions of less than 1% and around 6%, respectively, do not overlap. The findings in homozygous Hb CS contracdict prediction. There are four a-structural genes per normal human diploid genome. Hb CS trait is believed to be almost equivalent to a-thalassaemia 2 or a loss of one a-gene because HB CS, an a-variant, is barely or not detectable. Homozygosity for Hb CS has thus been predicted to be equivalent to a-thalassaemia 1 or a loss of two genes. The latter is asymptomatic and associated with microcytic-hypochromic red cells. However, Hb CS homozygosity presents with mild overt haemolytic anaemia and normal sized red cells. Pathogenesis associated with Hb CS inheritance is more complex than originally believed. There is a possibility that the unstable a^CS mRNAs precipitate and aggregate leading to pathology of red cells and to the basophilic stippling appearance, so striking in this syndrome.