How benign is sickle cell trait?

This is the authors' abstract. We don't add key points for this paper.

The complications of sickle cell disease (SCD) arise from the presence in red cells of the mutated haemoglobin, HbS, which replaces the normal adult Hb, HbA. HbS has a single amino acid substitution whereby valine replaces glutamic acid in the 6th codon of the β chain. Most SCD patients inherit two copies of the sickle gene (homozygous HbSS individuals - sometimes termed sickle cell anaemia, SCA). About a third of SCD patients co-inherit HbS with a second abnormal Hb, HbC, in which lysine replaces glutamic acid in the same codon (heterozygous HbSC individuals).