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Neuropsychiatric presentations are observed in a substantial number of patients with amyotrophic lateral sclerosis (ALS). Severe behavioral disorders develop in ALS combined with frontotemporal dementia, which are considered to be a disease continuum. Psychiatric disorders in ALS with predominantly motor symptoms are less prominent and mostly presented with apathy. Psychiatric disorders in ALS by their origin could be psychogenic, reflecting the patients' reactions on severe disease, and organic, developing as a result of degeneration of central motor neurons and disconnection between fronto-subcortical and frontotemporal loops. An important role in the development of psychiatric disorders in ALS belongs to genetic factors, in particular to hexanucleotide expansion in the C9orf72 gene. During the first months after establishing the diagnosis of ALS, there is the high risk of developing depressive disorders, which in severe cases can lead to suicide. More research is needed in this area.

Frontotemporal dementia is a progressive neurodegenerative disorder with high clinical, genetic, and pathomorphological diversity It is the third most common cause of dementia in all ages and the most common cause of early onset dementia (below 65). Despite its multifactorial nature, up to 40% of patients have a family history where the autosomal dominant inheritance type is seen in a quarter of cases. In this review, we describe key genes whose mutations can result in the development of frontotemporal dementia, the possible pathogenic mechanisms of the degenerative process, and provide information on the clinical features of the disease for different genetic variants. Special emphasis is placed on the frontotemporal dementia phenotype that is associated with amyotrophic lateral sclerosis.