Cognitive functioning in children with sickle cell disease: a meta-analysis.

OBJECTIVE To establish whether sickle cell disease (SCD) affects cognitive functioning in children with no evidence of cerebral infarction. METHODS We conducted a meta-analysis of studies of cognition in SCD to determine the size of any statistical difference between children with SCD and controls. Methodological factors were evaluated according to the size and frequency of group differences. RESULTS There were small but reliable decrements in cognitive functioning on IQ measures (4.3-point difference overall). The most methodologically rigorous studies showed a highly similar pattern. Sampling issues associated with the effect size for IQ were identified. Measures of specific abilities appear more sensitive than IQ scores to cognitive decrements in SCD. CONCLUSIONS SCD is associated with cognitive effects even in the absence of cerebral infarction. The causes of this cognitive decrement may include direct effects of SCD on brain function or indirect effects of chronic illness.