[Genetic modifiers of homozygous sickle cell disease]

Homozygous sickle cell (HbSS) disease is paradigmatic for the complex influence of genetic modifiers of a monogenic disease. The genetically determined variability of HbF concentration has a strong impact on the clinical phenotype. The pharmacologically induced increase of HbF leads to a reduced morbidity which demonstrates that the knowledge of genetic modifiers enables the development of new therapeutic strategies. The presence of alpha-thalassemia also ameliorates the disease phenotype albeit not to the same extent as HbF does. Both factors, HbF and alpha-thalassemia are insufficient to explain the clinical variability of HbSS disease. The introduction of genome analysis has now provided the tools to identify relevant gene loci that will likely be helpful in estimating the probability of severe complications such as the occurrence of stroke. Following the validation in prospective studies, the subtle analysis of genetic modifiers will therefore influence the management of patients with sickle cell disease.