The prevalence of "pure" autosomal dominant hereditary spastic paraparesis in the island of Ireland.

OBJECTIVES: Hereditary spastic paraparesis (HSP) is clinically and genetically heterogeneous. "Pure" autosomal dominant (AD) HSP is most common and eight genetic loci are identified to date. Previous studies have included autosomal recessive and sporadic cases in prevalence calculations. This study aimed to determine the prevalence and features of pure ADHSP in the island of Ireland.

METHODS: Index cases were identified from a 5 year survey of all adult and paediatric neurologists, clinical geneticists, hospital records, and hospital inpatient enquiry system data in Ireland, north and south. Families were examined by two neurologists and classified as affected or unaffected according to specific criteria. The prevalence date was set at 1 June 2000 and the midyear population estimate for the previous year was 5.436 million.

RESULTS: Eighty two patients with pure ADHSP and a further 12 obligate carriers from 19 families were identified. In total 69 patients with pure ADHSP were alive and resident in Ireland at the prevalence date. Twenty nine per cent of these were asymptomatic but with signs of paraparesis.

CONCLUSIONS: The prevalence of ADHSP in Ireland to estimated to be 1.27/100 000 population. The high proportion of asymptomatic cases and obligate carriers means that this condition is likely to be underdiagnosed.