Genetic contributions to human gyrification: sulcal morphometry in Williams syndrome.
Although gyral and sulcal patterns are highly heritable, and emerge in a tightly controlled sequence during development, very little is known about specific genetic contributions to abnormal gyrification or the resulting functional consequences. Williams syndrome (WS), a genetic disorder caused by hemizygous microdeletion on chromosome 7q11.23 and characterized by abnormal brain structure and striking cognitive (impairment in visuospatial construction) and behavioral (hypersocial/anxious) phenotypes, offers a unique opportunity to study these issues. We performed a detailed analysis of sulcal depth based on geometric cortical surface representations constructed from high-resolution magnetic resonance imaging scans acquired from participants with WS and from healthy controls who were matched for age, sex, and intelligence quotient, and compared between-group differences with those obtained from a voxel-based morphometry analysis. We found bilateral reductions in sulcal depth in the intraparietal/occipitoparietal sulcus (PS) in the brains of participants with WS, as well as in the collateral sulcus and the orbitofrontal region in the left hemisphere. The left-hemisphere PS in the WS group averaged 8.5 mm shallower than in controls. Sulcal depth findings in the PS corresponded closely to measures of reduced gray matter volume in the same area, providing evidence that the gray matter volume loss and abnormal sulcal geometry may be related. In the context of previous functional neuroimaging findings demonstrating functional alterations in the same cortical regions, our results further define the neural endophenotype underlying visuoconstructive deficits in WS, set the stage for defining the effects of specific genes, and offer insight into genetic mechanisms of cortical gyrification.