To estimate the prevalence rates for HA and HSP in eastern Quebec and to evaluate the frequency distribution of mutations associated with these disorders.

Regional epidemiological data on hereditary cerebellar ataxia (HA) and hereditary spastic paraplegia (HSP) are scarce.

We conducted an epidemiological study of patients who met clinical criteria for the diagnosis of and HSP in the east of the province of Quebec between January 2007 and July 2019. 238 HA patients and 112 HSP patients were examined by the same team of neurologists, using homogeneous inclusion criteria. The primary outcome was the prevalence per 100 000 persons with 95% confidence interval (CI) by subtype for eastern Quebec. The secondary outcome was the frequency of mutation assessed by targeted Next-generation Sequencing (NGS) approach. Minimum carrier frequency for identified variants was calculated based on allele frequency values and the Hardy-Weinberg (HW) equation.

HA prevalence in the region was estimated at 6.28/100 000 [95% CI; 6.18-6.38]: 3.73/100 000 for autosomal-dominant and 2.49/100 000 for autosomal recessive. HSP prevalence was 3.98/100 000 [95% CI; 3.85-4.11]: 1.97/100 000 for autosomal dominant-hereditary spastic paraplegia and 2/100 000 for autosomal recessive-hereditary spastic paraplegia. Autosomal recessive cerebellar ataxia type 1 (ARCA1; 2.67/100 000) and autosomal dominant spastic paraplegia SPG4 (1.18/100 000) were the most prevalent form in eastern Quebec. 52.4% of patients had a confirmed genetic diagnosis. Mutations were identified in 23 different genes and molecular alterations in 6 trinucleotides repeats expansion; the most common mutation were c.15705-12A>G in SYNE1 gene (minimum carrier frequency 1/134) and c.1529 C>T (1/200) in SPG7 gene.

We described for the first time the minimum prevalence of genetically defined HA and HSP in eastern Quebec although somes figures may be an underestimate of the true prevalence. The data provide a framework for international comparison and service planning.