Investigators at the Kennedy Krieger Institute, Johns Hopkins University School of Medicine, have compared posterior vermis size (cross-sectional area) measured by MRI in 32 males with fragile X syndrome (fra X), 28 males with other causes of cognitive disability (CD), 38 males with normal development (ND), and 37 females with fra X and 53 female control subjects. Neurocognitive correlates of posterior vermis size were also examined in females with fra X. Posterior vermis size was decreased in fra X subjects, males more than females, and the decrease was greater after adjusting for intracranial area. Performance on the WISC-R, WAIS-R, block design, Wisconsin Card Sorting Test, and the Rey inventory correlated with posterior vermis size in female fra X patients. The correlation was stronger for the verbal IQ than the performance IQ scores. 
COMMENT. Cerebellar posterior vermal hypoplasia is a developmental anomaly in patients with fragile X syndrome, and males are more severely affected than females. Decreases in size of the posterior vermis in female fra X patients correlate with impaired performance on selected neurocognitive tests. The cerebellar vermis is involved in cognitive processes, especially in tasks dependent on visual-spatial perception, areas deficient in female fra X subjects.
Hypoplasia of the cerebellum and of the splenium of the corpus callosum, and other cerebral anomalies have been reported in children with attention deficit hyperactivity disorder, a frequent complication of fragile X syndrome. (Progress in Pediatric Neurology III, PNB Publishers, 1997;212-213).