CD6 and sickle cell disease: Missense mutations like Cd6 GAG > GTG (HBB:c.20A > T, p.Glu6Val), the classical cause of sickle cell disease (HbSS) mutation, and frameshift deletions like Cd5-CT (HBB:c.17_18delCT) were found at lower frequency (2.5–17.5%) and were deemed pathogenic because of their disruptive effects on protein structure and function.