ATXN2 polyQ intermediate repeats are a modifier of ALS survival

Objective: To analyze the frequency and clinical characteristics of patients with amyotrophic lateral sclerosis (ALS) with intermediate-length (CAG) expansion (encoding 27–33 glutamines, polyQ) in the ATXN2 gene, in a population-based cohort of Italian patients with ALS (discovery cohort), and to replicate the findings in an independent cohort of consecutive patients from an ALS tertiary center (validation cohort). Methods: PolyQ repeats were assessed in 672 patients with incident ALS in Piemonte and Valle d'Aosta regions, Italy, in the 2007–2012 period (discovery cohort); controls were 509 neurologically healthy age- and sex-matched subjects resident in the study area. The validation cohort included 661 patients with ALS consecutively seen between 2001 and 2013 in the ALS Clinic Center of the Catholic University in Rome, Italy. Results: In the discovery cohort, the frequency of ≥31 polyQ ATNX2 repeats was significantly more common in ALS cases (19 patients vs 1 control, p = 0.0001; odds ratio 14.8, 95% confidence interval 1.9–110.8). Patients with an increased number of polyQ repeats had a shorter survival than those with <31 repeats (median survival, polyQ ≥31, 1.8 years, interquartile range [IQR] 1.3–2.2; polyQ <31, 2.7 years, IQR 1.6–5.1; p = 0.001). An increased number of polyQ repeats remained independently significant at multivariable analysis. In the validation cohort, patients with ≥31 polyQ repeats had a shorter survival than those with <31 repeats (median survival, polyQ ≥31, 2.0 years, IQR 1.5–3.4; polyQ <31, 3.2 years, IQR 2.0–6.4; p = 0.007). Conclusions: ATXN2 polyQ intermediate-length repeat is a modifier of ALS survival. Disease-modifying therapies targeted to ATXN2 represent a promising therapeutic approach for ALS.