GSTM1 and sickle cell disease: However, a lower D42 Hb concentration was associated with either α-thalassaemia genotype (potentially reflecting normal physiology), sickle cell disease, or failing treatment; whilst the latter has been previously reported in two studies [26, 45], it was not a factor in Zwang et al.’s meta-analysis of posttreatment anaemia in patients of all ages [21].