Sickle cell disease.

Sickle cell disease (SCD) is an inherited hemoglobinopathy caused by a mutation in the sixth amino acid of the β-globin gene (HBB). It is the most common serious genetic diseases in childhood, affecting approximately 1 in 2500 births and 100 000 individuals in the USA, in addition to 300 000 new cases globally each year. Central nervous system injury is the most debilitating frequent complication of SCD and includes stroke, silent cerebral infarct (SCI), and cognitive impairment. Among children with sickle cell anemia (HbSS), 11% had a stroke by age 18 years before the implementation of transcranial Doppler screening. SCI is identified in 27% of children with HbSS by their 5th birthday. Children who develop SCI have greater cognitive impairment compared with either children with HbSS without SCI or siblings without SCD. A recent study of adults demonstrated significant cognitive dysfunction, even in participants with apparently mild SCD.