Introduction Amyotrophic lateral sclerosis (ALS) individuals carrying the hexanucleotide repeat expansion (HRE) in the C9orf72 gene (C9Pos) have been described as presenting distinct features compared to the general ALS population (C9Neg). We aim to identify the phenotypic traits more closely associated with the HRE and analyse the role of the repeat length as a modifier factor. Methods We studied a cohort of 960 ALS patients (101 familial and 859 sporadic cases). Motor phenotype was determined using the MRC scale, the lower motor neuron score (LMNS) and the Penn upper motor neuron score (PUMNS). Neuropsychological profile was studied using the Italian version of the Edinburgh Cognitive and Behavioral ALS Screen (ECAS), the Frontal Behavioral Inventory (FBI), the Beck Depression Inventory-II (BDI-II) and the State-Trait Anxiety Inventory (STAI). A two-step PCR protocol and Southern blotting were performed to determine the presence and the size of C9orf72 HRE, respectively. Results C9orf72 HRE was detected in 55/960 ALS patients. C9Pos patients showed a younger onset, higher odds of bulbar onset, increased burden of UMN signs, reduced survival and higher frequency of concurrent dementia. We found an inverse correlation between the HRE length and the performance at ECAS ALS-specific tasks (P = 0.031). Patients also showed higher burden of behavioural disinhibition (P = 1.6 × 10–4), lower degrees of depression (P = 0.015) and anxiety (P = 0.008) compared to C9Neg cases. Conclusions Our study provides an extensive characterization of motor, cognitive and behavioural features of C9orf72-related ALS, indicating that the C9orf72 HRE size may represent a modifier of the cognitive phenotype.

Objective:Although oculomotor abnormalities (OMAs) are not usually considered prominent features of amyotrophic lateral sclerosis (ALS), they may represent potential clinical markers of neurodegeneration, especially when investigated together with cognitive and behavioral alterations. The aim of our study was to identify patterns of clinically evident OMAs in ALS patients and to correlate such findings with cognitive-behavioral data.Methods: three consecutive, inpatient cohorts of Italian ALS patients and controls were retrospectively evaluated to assess the frequency of OMAs and cognitive-behavioral alterations. The ALS population was divided in a discovery and a replication cohort. Controls included a cohort of cognitively impaired individuals and of patients with Alzheimer’s disease (AD). Subjects underwent bedside eye movement evaluation to determine the presence and pattern of OMAs. Cognitive assessment was performed using a standard neuropsychological battery (discovery ALS cohort, and AD cohort), and the Italian Edinburgh Cognitive and Behavioural ALS Screen – ECAS (replication ALS cohort).Results:We recruited 864 ALS (635 discovery, 229 replication), 798 cognitively unimpaired, and 171 AD subjects. OMAs were detected in 10.5% of our ALS cohort vs 1.6% of cognitively unimpaired controls (p=1.2x10-14) and 11.4% of AD patients (p=ns). The most frequent deficits were smooth pursuit and saccadic abnormalities. OMAs frequency was higher in patients with bulbar onset, prominent upper motor neuron signs, and advanced disease stages. Cognitive dysfunction was significantly more frequent in patients with OMAs in both ALS cohorts (p=1.1x10-25). Furthermore, OMAs significantly correlated with the severity of cognitive impairment and with pathological scores at the ECAS ALS-specific domains. Lastly, OMAs could be observed in 35.0% of cognitively impaired ALS vs 11.4% of AD patients (p=6.4x10-7), suggesting a possible involvement of frontal oculomotor areas in ALS.Discussion:ALS patients showed a range of clinically evident OMAs, and these alterations were significantly correlated with cognitive, but not behavioral, changes. OMAs may be a marker of neurodegeneration and bedside assessment represents a rapid, highly specific tool for detecting cognitive impairment in ALS.