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Background: Amyotrophic lateral sclerosis (ALS) is a rare disease with urgent need for improved treatment. Despite the acceleration of research in recent years, there is a need to understand the full natural history of the disease. As only 40% of people living with ALS are eligible for typical clinical trials, clinical trial datasets may not generalize to the full ALS population. While biomarker and cohort studies have more generous inclusion criteria, these too may not represent the full range of phenotypes, particularly if the burden for participation is high. To permit a complete understanding of the heterogeneity of ALS, comprehensive data on the full range of people with ALS is needed., Methods: The ALS Natural History Consortium (ALS NHC) consists of nine ALS clinics and was created to build a comprehensive dataset reflective of the ALS population. At each clinic, most patients are asked to participate and about 95% do. After obtaining consent, a minimum dataset is abstracted from each participant's electronic health record. Participant burden is therefore minimal., Results: Data on 1925 ALS patients were submitted as of 9 December 2022. ALS NHC participants were more heterogeneous relative to anonymized clinical trial data from the Pooled Resource Open-Access ALS Clinical Trials (PRO-ACT) database. The ALS NHC includes ALS patients of older age of onset and a broader distribution of El Escorial categories, than the PRO-ACT database., Conclusions: ALS NHC participants had a higher diversity of diagnostic and demographic data compared to ALS clinical trial participants.Key Messages What is already known on this topic: Current knowledge of the natural history of ALS derives largely from regional and national registries that have broad representation of the population of people living with ALS but do not always collect covariates and clinical outcomes. Clinical studies with rich datasets of participant characteristics and validated clinical outcomes have stricter inclusion and exclusion criteria that may not be generalizable to the full ALS population. What this study adds: To bridge this gap, we collected baseline characteristics for a sample of the population of people living with ALS seen at a consortium of ALS clinics that collect extensive, pre-specified participant-level data, including validated outcome measures.How this study might affect research , practice, or policy: A clinic-based longitudinal dataset can improve our understanding of the natural history of ALS and can be used to inform the design and analysis of clinical trials and health economics studies, to help the prediction of clinical course, to find matched controls for open label extension trials and expanded access protocols, and to document real-world evidence of the impact of novel treatments and changes in care practice.

Over the past two decades, the El Escorial criteria (EEC) have been used as eligibility criteria in major randomized controlled trials. One of the goals of the revised EEC was to allow earlier diagnosis and, thus earlier trial inclusion by introducing a new category, namely "clinically probable laboratory supported" ALS. This category allowed EMG findings to be taken into account assuming that EMG is more sensitive than the clinical examination in detecting lower motor neuron signs. Recently, Edaravone has been licensed in several countries for the treatment of ALS based on a randomized controlled trial in a selected group of ALS patients excluding the EEC category "clinically probable laboratory supported". The major reason was that in a post hoc analysis of the first Edaravone trial this group comprised many slow progressors. As it is unclear whether this bias towardslow progressors was a study-specific problem or related to the category itself, we performed an analysis in the PRO-ACT dataset. In the PRO-ACT dataset, progression in ALS patients included at baseline into the "clinically probable laboratory supported" category was significantly slower (-0.53 in ALSFRS/month) compared to the other EEC categories (-0.68 in ALSFRS/month; p  < 0.001) and exhibited a significantly longer diagnostic delay (13.5 months vs. 11.7 months, p  < 0.001). This suggests that the bias toward slow progressors in the "clinically probable laboratory supported" category is an inherent problem of the category and thus does not fulfill the previous goal of earlier diagnosis, raising several questions concerning the application of this category.