The majority of Huntington's disease (HD) mutation carriers experience some psychopathology during their lifetime, varying from irritability to psychosis, but prevalences of particular symptoms vary widely due to diverse study populations in different stages of HD and the use of different assessment methods.

The study population consisted of 1993 HD mutation carriers from 15 European countries, all participating in the observational REGISTRY study. The behavioural section of the Unified HD Rating Scale was used to examine the prevalence and correlates of five neuropsychiatric features: depression, irritability/aggression, obsessive/compulsive behaviours, apathy and psychosis.

Twenty-seven per cent of the participants did not have any neuropsychiatric symptom in the last month. Moderate to severe apathy occurred in 28.1% of the participants, whereas moderate to severe depression was found in 12.7%. Irritable/aggressive symptoms were present in 13.9% of the participants, and 13.2% showed obsessive/compulsive behaviours. Moderate to severe psychotic symptoms were found in only 1.2%. Only 54.9% of all participants with moderate to severe depression used antidepressants, suggesting undertreatment of depression. Obsessive/compulsive behaviours and irritability/aggression were inversely correlated with the Total Functional Capacity score, but with apathy showing the strongest inverse association.

A variety of neuropsychiatric symptoms are highly prevalent in different stages of HD in this European HD population, with apathy as the most frequent symptom. Depression, irritability/aggression and OCBs are prevalent in all stages of HD. Apathy was the key neuropsychiatric symptom occurring most often in advanced HD stages. Due to possible selection of relatively healthy participants, prevalences reported in this study might be an underestimation of prevalence in the entire HD population.