Academic achievement in individuals with infantile nephropathic cystinosis.

The present study examined academic skills in children and young adults with infantile nephropathic cystinosis. Cystinosis is a genetic metabolic disorder in which the amino acid cystine accumulates in various tissues and organs, including the kidney, cornea, thyroid, and brain. Individuals with cystinosis have normal intelligence but subtle visual processing impairments. Subjects were 19 children and young adults with cystinosis and 19 age-, sex-, and IQ-matched controls. All subjects had IQs within the normal range. On a test of academic achievement, mean standard scores for cystinosis and control subjects, respectively, were as follows: arithmetic 89.95 +/- 13.77 vs. 102.16 +/- 9.62; spelling 90.68 +/- 18.81 vs. 98.00 +/- 10.96; reading 97.47 +/- 15.59 vs. 98.58 +/- 12.41. Multivariate analysis of variance revealed a significant main effect for Group (P = .009); there was no main effect for Sex, nor was there a Group x Sex interaction. Univariate follow-up tests indicated that the cystinosis group performed significantly more poorly than did controls on the arithmetic subtest (P = .001) and that there was a trend (P = .085) toward poorer performance by the cystinosis group on the spelling subtest. Regression analyses revealed no evidence of a developmental lag or deterioration of function with age. The visual processing deficits previously identified in these individuals may underlie the academic difficulties observed here. It is possible that both visual processing and academic difficulties may reflect a common mechanism of selective cortical damage by this genetic defect.