Dystonia-predominant adult-onset Huntington disease: Association between motor phenotype and age of onset in adults

Backgrounds: In juvenile Huntington disease (HD), dystonia as well as parkinsonism and eye movement abnormalities may be the predominant motor signs rather than chorea. Several patients have come to our attention with adult-onset HD in whom there is prominent dystonia and minimal chorea (ie, an adult-onset form of HD that resembles juvenile HD). Objectives: To estimate the prevalence of these cases of dystonia-predominant HD in a clinic and to study the relationship between the motor phenotype and age of onset in HD. Methods: The Unified Huntington's Disease Rating Scale (UHDRS) was administered to 127 subjects during their initial visit to the Huntington's Disease Center at the New York State Psychiatric Institute, where dystonia, chorea, bradykinesia, rigidity, and eye movements were rated. The dystonia score was the mean UHDRS rating of dystonia in 5 body regions; the chorea score, the mean rating of chorea in 7 regions; the bradykinesia score, the mean rating of axial and limb bradykinesia; the rigidity score, the mean rating of rigidity in both arms; and the eye movement score, the mean rating of ocular pursuit, saccade initiation, and velocity. Dystonia-predominant HD was defined by the severity of dystonia relative to the severity of chorea. Results: Fifteen (11.8%) of 127 subjects had dystonia-predominant HD. Age of onset correlated negatively (r=-0.22, P=.02) with the dystonia score divided by the chorea score and negatively (r=-0.28, P= .002) with the severity of dystonia, bradykinesia, and eye movement abnormalities relative to chorea (ie, [(dystonia score + bradykinesia score + eye movement score)/3] - chorea score), suggesting that subjects with younger ages of onset had more severe dystonia, bradykinesia, and eye movement abnormalities relative to chorea. Conclusions: Cases of adult-onset HD with prominent dystonia and a paucity of chorea may represent 1 in 8 cases in specialty clinics. Age of onset was clearly associated with the motor phenotype. A younger age of onset was associated with more severe dystonia, bradykinesia, and eye movement abnormalities relative to chorea, supporting the notion that in adult-onset HD, the motor phenotype forms a continuum with respect to age of onset.