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Decreased Density of Cholinergic Interneurons in the Medial Caudate Nucleus in Humans with Williams Syndrome

Williams syndrome (WS) is a rare neurodevelopmental disorder caused by the hemideletion of approximately 25–28 genes at 7q11.23. Its unusual social and cognitive phenotype is most strikingly characterized by the disinhibition of social behavior, in addition to reduced global IQ, with a relative sparing of language ability. Hypersociality and increased social approach behavior in WS may represent a unique inability to inhibit responses to specifically social stimuli, and is likely rooted in part in abnormalities of frontostriatal circuitry. Recent research has demonstrated that selective ablation of striatal cholinergic interneurons (SCINs) results in significant increases in compulsive conspecific‐directed, but not object‐focused, exploratory behavior in mice, indicating a role for SCINs in social approach behavior. Here, we examined the density of SCINs and parvalbumin‐positive interneurons in the striatum of five postmortem specimens from subjects with WS and five typically‐developing (TD) subjects. We found a significant reduction in the density of SCINs in the medial caudate nucleus, an important region receiving cortical projections from the orbitofrontal and ventromedial prefrontal cortex in circuitry involved in language and reward systems. This pattern of decreased SCIN density in WS is contrasted by anatomical findings in other disorders, including Tourette syndrome and schizophrenia, where differing patterns of SCIN depletion are found. Taken together with findings from neuroimaging, differences in the brains of individuals with WS at both the macro‐ and microstructural level further indicate a role for frontostriatal circuitry in the disorder's distinctive behavioral phenotype.