Huntington’s disease (HD) is a lethal, dominantly inherited neurodegenerative disorder reported to be unusually rare in Finland. The overall HD prevalence and the proportion of late-onset cases (LOHD) are increasing in many populations. The characteristics of LOHD are nevertheless poorly understood. Information on neurological comorbidity in patients with HD is also scarce. These retrospective studies analyzed a national Finnish HD cohort in the time frame 1987-2010 by searching national registries and archives. Data was extracted from medical records. Population genotypes were obtained from the 1000 Genomes project. 

The prevalence of HD in Finland was found to be 2.12/100,000, or over four times more common than reported previously. Nonetheless, HD is more uncommon than in other Western European countries. The national cohort of 207 patients included 52 (25%) patients with LOHD; they had poorer motor status at the time of diagnosis than patients with mid-age onset, possibly because of the diagnostic delay. No other differences were detected between these groups. Interestingly, only one individual (0.5% of all HD patients in Finland) with juvenile-onset HD was identified. 

The length of the affected CAG repeat or its intergenerational stability did not differ from those reported in other populations. However, the high risk chromosome 4 haplogroup A was relatively uncommon in the Finnish general population (39.2%), possibly partly explaining the relative rarity of HD in Finland. 

Patients with adult-onset HD had epilepsy and strokes as often as reported in the general population. HD patients were, however, at an increased risk of suffering subdural haematomas.