Emerging strategies for interpreting variants of uncertain significance (VUS) in amyotrophic lateral sclerosis

As the use of genetic testing for neurological diseases increases exponentially, interpreting variants of uncertain significance (VUS) has become a challenging problem. Nowhere has this become more evident than in amyotrophic lateral sclerosis (ALS) and the frontotemporal dementias (FTDs), both of which are complex heterogeneous disorders in which an increasing array of disease-causative and modifying genetic variants are observed. Moreover, while traditionally identified as distinct clinical syndromes, ALS and FTD are increasingly recognized to exist along a spectrum of clinical syndromes (termed the frontotemporal spectrum disorders of ALS; ALS-FTSD) with shared genetic risk. While VUS are generally not used in clinic for decision-making or counseling given their obvious limitations in being medically actionable, their correct interpretation is dynamic and rapidly evolving. VUS are increasingly the subject of intensive study as potential determinants of biological outcomes. It is timely therefore to review the current state of VUS interpretation and to critically evaluate how this can be applied to enhance both patient care and treatment decisions in the broader context of neurological disorders and more specifically in the context of ALS and ALS-FTSD. In doing so, we also explore the evolving challenge of defining pathogenicity of oligogenic inheritance in the context of multiple VUS detection in a single individual using an illustrative case example.