Sickle-cell disease (SCD) is an autosomal recessive disorder caused by an A·T-to-T·A mutation in the haemoglobin subunit beta (HBB) gene, resulting in the pathogenic sickle-cell allele (HBBS) encoding a Glu 6→Val (E6V) substitution. This evidence concerns the gene HBB and sickle cell disease.