The neurobiology of Williams syndrome: cascading influences of visual system impairment?

Williams syndrome (WS) is characterized by a unique pattern of cognitive, behavioral, and neurobiological findings that stem from a microdeletion of genes on chromosome 7. Visuospatial ability is particularly affected in WS and neurobiological studies of WS demonstrate atypical function and structure in posterior parietal, thalamic, and cerebellar regions that are important for performing space-based actions. This review summarizes the neurobiological findings in WS, and, based on these findings, we suggest that people with WS have a primary impairment in neural systems that support the performance of space-based actions. We also examine the question of whether impaired development of visual systems could affect the development of atypical social-emotional and language function in people with WS. Finally, we propose developmental explanations for the visual system impairments in WS. While hemizygosity for the transcription factor II-I gene family probably affects the development of visual systems, we also suggest that Lim-kinase 1 hemizygosity exacerbates the impairments in performing space-based actions.