Knight, Susan N.; Singhal, Atul; Thomas, Peter W.; Serjeant, Graham R.
Author Affiliation, Ana.
Medical Research Council Laboratories (Sickle Cell)
Factors associated with lowered intelligence in homozygous sickle cell disease.
Archives of Disease in Childhood
Date of Publication
Assesses the intelligence quotient (IQ) of 60 patients with homozygous sickle cell (SS) disease and 60 age and sex matched controls with a normal haemoglobin (AA) genotype aged 15-18 years, followed up in a cohort study from birth, by the Wechsler intelligence scales for children and adults. IQ appeared to be normally distributed in both genotypes but mean values in SS disease were 5.6 points (95 percent confidence interval (CI) 1.0 to 10.2) lower than in AA controls (p=0.016). The difference occurred in both verbal (5.5 points, p=0.017) and performance (5.0 points, p=0.044) subscales of the IQ defect in SS disease was associated with a significantly lower attention factor score (p=0.005) but not with other factor scores. The genotype difference in IQ was not accounted for by differences in parental occupational level, school absenteeism, or school drop out, or reported activity level. In SS disease, IQ was not related to mean steady state haemoglobin, or mean cell haemoglobin concentration, or clinical severity as judged by the frequency of painful crises, hospital admission, or sick visits. IQ, at age 15-18 years, correlated with the patients' height at all ages from 1 to 10 years (partial correlations increasing from 0.14 (p=0.15) at age 1 to 0.27 (p=0.004) at age 10). Adjusting for height reduced the mean genotype difference in IQ to 5.5 (95 percent CI 0.6 to 10.3) points at age 1 and 10 2.6 points (95 percent CI 0.6 to 10.3) points at age 10. Prepubertal height therefore accounted for much of the genotype difference in IQ. It is speculated that early factors, possibly nutritional, contribute to both impaired growth and mental development in sickle cell disease.....