Impact of Chromosome 7q11.23 Copy Number Variation on Hippocampal Volume Studied Longitudinally in Children and Adolescents

Williams syndrome (WS) results from hemideletion of ∼25 genes on chromosome 7q11.23, whereas 7q11.23 duplication syndrome (Dup7) results from an extra copy of the same genes. Interestingly, WS is typified by increased social drive (often termed “hypersociability”), non-social anxiety, and visuospatial cognitive deficits; whereas individuals with Dup7 often have social phobia and different cognitive features. Studying Dup7, in conjunction with WS, thus, allows for examination of gene dosage effects on brain and behavior. Previous work found that children/adolescents with WS have relatively larger hippocampal volumes than do typically developing children/adolescents (TDs). We hypothesized that, in contrast to WS, relative hippocampal volumes in children/adolescents with Dup7 would be smaller than TDs, consistent with a gene-dosage effect.