Genetics screening in an Italian cohort of patients with Amyotrophic Lateral Sclerosis: the importance of early testing and its implication.

INTRODUCTION: Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease with an elusive etiology. While environmental factors have been considered, familial ALS cases have raised the possibility of genetic involvement. This genetic connection is increasingly evident, even in patients with sporadic ALS. We allowed access to the genetic test to all patients attending our clinic to identify the prevalence and the role of genetic variants in the development of the disease and to identify patients with potentially treatable forms of the disease.

MATERIALS AND METHODS: 194 patients with probable or definite ALS, were enrolled. A comprehensive genetic testing was performed, including sequencing all exons of the SOD1 gene and testing for hexanucleotide intronic repeat expansions (G4C2) in the C9orf72 gene using fluorescent repeat-primed PCR (RP-PCR). Whole Exome NGS Sequencing (WES) was performed, followed by an in silico multigene panel targeting neuromuscular diseases, spastic paraplegia, and motor distal neuropathies. We conducted statistical analyses to compare different patient groups.

RESULTS: Clinically significant pathogenetic variants were detected in 14.43% of cases. The highest prevalence of pathogenetic variants was observed in fALS patients, but a substantial proportion of sALS patients also displayed at least one variant, either pathogenetic or of uncertain significance (VUS). The most observed pathogenetic variant was the expansion of the C9orf72 gene, which was associated with a shorter survival. SOD1 variants were found in 1.6% of fALS and 2.5% of sALS patients.

DISCUSSION: The study reveals a significant number of ALS patients carrying pathogenic or likely pathogenic variants, with a higher prevalence in familial ALS cases. The expansion of the C9orf72 gene emerges as the most common genetic cause of ALS, affecting familial and sporadic cases. Additionally, SOD1 variants are detected at an unexpectedly higher rate, even in patients without a familial history of ALS, underscoring the crucial role of genetic testing in treatment decisions and potential participation in clinical trials. We also investigated variants in genes such as TARDBP, FUS, NEK1, TBK1, and DNAJC7, shedding light on their potential involvement in ALS. These findings underscore the complexity of interpreting variants of uncertain significance (VUS) and their ethical implications in patient communication and genetic counseling for patients' relatives.

CONCLUSION: This study emphasizes the diverse genetic basis of ALS and advocates for integrating comprehensive genetic testing into diagnostic protocols. The evolving landscape of genetic therapies requires identifying all eligible patients transcending traditional familial boundaries. The presence of VUS highlights the multifaceted nature of ALS genetics, prompting further exploration of complex interactions among genetic variants, environmental factors, and disease development.