Hereditary ataxia and spastic paraplegia in Portugal: a population-based prevalence study.

IMPORTANCE: Epidemiological data on hereditary cerebellar ataxia (HCA) and hereditary spastic paraplegia (HSP) are scarce. OBJECTIVE: To present the prevalence and distribution of HCA and HSP in Portugal. DESIGN AND SETTING: Population-based, nationwide, systematic survey, from January 1, 1994, through April 15, 2004, in Portugal. PARTICIPANTS: Multiple sources of information were used (review of clinical files, active collaboration of neurologists and geneticists, and investigation of affected families), but the main source was active collaboration of general practitioners. Patients were examined by the same team of neurologists, using homogeneous inclusion criteria. The clinical data were registered, and all families were genetically tested. RESULTS: Overall, 1336 patients from a population of 10,322 million were diagnosed as having HCA or HSP, a prevalence of 12.9 per 100,000 population. Hereditary cerebellar ataxia was more prevalent (prevalence, 8.9 per 100,000 population; 5.6 for dominant and 3.3 for recessive ataxias) than HSP (prevalence, 4.1 per 100,000 population; 2.4 for dominant and 1.6 for recessive). Machado-Joseph disease (spinocerebellar ataxia type 3) (prevalence, 3.1 per 100,000 population), Friedreich ataxia (prevalence, 1.0 per 100,000 population), and ataxia with oculomotor apraxia (prevalence, 0.4 per 100,000 population) were the most frequent HCAs. Spastic paraplegia types 4 (prevalence, 0.91 per 100,000 population), 3 (prevalence, 0.14 per 100,000 population), and 11 (prevalence, 0.26 per 100,000 population) were the most prevalent HSPs. CONCLUSIONS AND RELEVANCE: This population-based survey covered all the Portuguese territory and mobilized most general practitioners and health centers. To our best knowledge, this survey was the largest ever performed for HCA and HSP. Prevalence of autosomal dominant ataxias was high, particularly for Machado-Joseph disease (spinocerebellar ataxia type 3). The genetic cause has not been identified in 39.7% of the patients studied.