C9orf72 gene repeat expansion phenotype profile of motor neurone disease in Portugal

Background C9orf72 gene repeat expansion (C9RE) is the most frequent gene variant associated with amyotrophic lateral sclerosis (ALS). We aimed to study the phenotype of motor neurone disease (MND) patients with C9RE in a Portuguese cohort. Methods Demographical and clinical data of MND patients with (C9RE+) and without C9RE were compared. ALS al Rating Scale-Revised (ALSFRS-R) and Edinburgh Cognitive and Behavioural ALS Screen (ECAS) were used to evaluate functional and cognitive performance, respectively. Survival analysis was performed using Kaplan Meier log-rank test and Cox proportional hazards model. Results We included 761 patients of whom 61 (8.0 %) were C9RE+. C9RE+ patients had a higher frequency of ALS (95.1 vs 78.4 %, p = 0.002), and lower frequency of progressive muscular atrophy (3.3 vs 16.7 %, p = 0.006). C9RE+ was associated with earlier age of onset (58.1 vs 62.6 years, p = 0.003) and more frequent MND family history (65.5 vs 11.4 %, p < 0.001). Gender, ethnicity, onset site, diagnostic delay, disease progression rate until diagnosis (Delta F), ALSFRS-R and time until non-invasive ventilation did not differ between groups. Cognitive/behavioural symptoms and ECAS did not differ between groups, except a worse visuospatial score in C9RE+ group (p = 0.035). Death rate was 1.8 and 1.6 times higher in C9RE+ patients with MND and ALS, respectively. Significant survival prognostic factors in C9RE+ group were diagnosis delay (HR = 0.96, 95 %CI 0.92-0.99, p = 0.008) and Delta F (HR = 1.93, 95 %CI 1.26-2.96, p = 0.002). Conclusion Our study corroborates most previous cohorts' findings, but harbours some singularities regarding onset site, phenotype, and cognitive profile, that contribute to a better understanding of C9RE epidemiology.