Movement disorder in Down's syndrome: a possible marker of the severity of mental handicap.

This study examined the nature and prevalence of abnormal movements in adults with Down's syndrome and also the clinical correlates of orofacial dyskinesia and the relationship between dyskinesia and the level of functional and intellectual disability. Movement disorder, language age, and disability were assessed in an epidemiologically based sample of 145 individuals with Down's syndrome. Abnormal involuntary movements were common, with > 90% exhibiting dyskinesia, predominantly orofacial. Stereotypes were present in one-third of the sample. There was an association between the severity of dyskinesia and both current language age and functioning in terms of self-care and practical and academic skills, which suggested that dyskinesia may be a marker of the severity of mental handicap. The presence of dyskinesia was unrelated to neuroleptic exposure. Dyskinesia and stereotypies are very common in individuals with Down's syndrome and may represent an inherent manifestation of the disorder. The relationship between mental age and dyskinesia in Down's syndrome warrants further research.