Purpose: Prader-Willi syndrome is a well-defined genetic cause of childhood-onset obesity that can serve as a model for investigating early-onset childhood obesity. Individuals with Prader-Willi syndrome have speech and language impairments, suggesting possible involvement of the perisylvian region of the brain. Clinical observations suggest that many individuals with early-onset morbid obesity have similar speech/language deficits, indicating possible perisylvian involvement in these children

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... s well. We hypothesized that similar perisylvian abnormalities may exist in both disorders. Methods: Participants included individuals with Prader-Willi syndrome (n ϭ 27), their siblings (n ϭ 16), individuals with early-onset morbid obesity (n ϭ 13), and their siblings (n ϭ 10). Quantitative and qualitative assessments of sylvian fissure conformation, insula closure, and planum temporale length were performed blind to hemisphere and diagnosis. Results: Quantitative measurements verified incomplete closure of the insula in individuals with Prader-Willi syndrome. Planar asymmetry showed its normal bias toward leftward asymmetry in all groups except those with Prader-Willi syndrome maternal uniparental disomy. Individuals with Prader-Willi syndrome and siblings had a normal distribution of sylvian fissure types in both hemispheres, while individuals with early-onset morbid obesity and their siblings had a high proportion of rare sylvian fissures in the right hemisphere. Conclusions: The contrast between the anatomic findings in individuals with Prader-Willi syndrome and early-onset morbid obesity suggests that the language problems displayed by children with these two conditions may be associated with different neurodevelopmental processes. Genet Med 2007:9(8):536-543.