Background and Objectives:SOD1 variants in patients with amyotrophic lateral sclerosis (ALS) have been associated to peculiar clinical features and disease progression but rarely to cognitive and behavioural impairment. This study aims at describing the features of frontotemporal syndromes in ALS patients carrying SOD1 variants.Methods:Italian patients with ALS were consecutively enrolled between 2012 and 2020 at our Motor Neuron Disease center. All underwent clinical assessment, extensive neurophysiological test battery for the evaluation of cognitive functions and behavior, and targeted next generation sequencing of SOD1, FUS, TARDBP, VCP, PFN1, TUBA4A, OPTN, SQSTM1, UBQLN2 and C9orf72 genes. Neuropsychological profiles of SOD1+ patients (SOD1+) were compared to those with no gene variants (SOD1-). To this aim, the occurrence of cognitive and behavioral impairment defined according to current guidelines, the number of pathological test performances based on Italian normative values, and scores of the Frontal Behavioural Inventory were collected.Results:Among 288 patients consecutively examined, we identified 8 known pathogenic SOD1 variants and one variant of uncertain significance (p.Ser26Asn) not previously described in 14 ALS patients belonging to 11 families. The clinical phenotypes were mainly characterized by predominant lower motor neuron involvement with onset at the lower limbs, and one patient had bulbar onset. SOD1+ patients (n=14) were compared to SOD1- patients (N = 274). SOD1+ patients were younger than SOD1-, and both groups had similar functional motor disabilities and disease duration. Based on the overall neuropsychological findings, the percentage of SOD1+ and SOD1- patients with altered profiles were about 60%. However, behavioral impairment defined by the Strong criteria, and most commonly featuring with irritability and mental rigidity, was more frequent in SOD1+ than SOD1- patients, and mainly associated with variants in exon 5. Conversely, cognitive impairment was mainly found in SOD1- patients.Discussion:Our findings from a large cohort of deeply phenotyped ALS patients demonstrated that behavioral involvement is more common than previously thought among patients harboring SOD1 variants, and that it is independent from patients’ age and disease stage. These findings could be relevant for the assessment of clinical trial outcomes and disease management.