Improving ALS Molecular Diagnosis Through Functional Assays: Reassessment of a SOD1 Variant of Uncertain Significance

TL;DR

This study improves ALS diagnosis by using functional tests to determine if a genetic variant is harmful, helping avoid misdiagnosis and enabling timely treatment.

Contribution

A rapid functional assessment pipeline is developed to reclassify SOD1 variants of uncertain significance in ALS.

Findings

The SOD1 p.Val120Leu variant was reclassified as pathogenic based on functional assays.

The variant caused cytoplasmic aggregation and reduced neurite outgrowth in zebrafish.

Abnormal motor behavior in zebrafish further supported the variant's pathogenicity.

Abstract

Genetic testing in amyotrophic lateral sclerosis (ALS) often reveals variants of uncertain significance (VUS), which are frequently omitted from diagnostic reports or reported with limited clinical interpretation. To address this gap, we developed a rapid functional assessment pipeline in collaboration with FILSLAN, the French ALS care network, combining in vitro and in vivo neurogenetic assays. We illustrate this approach through the reclassification of the SOD1 p.Val120Leu variant, identified in an ALS patient, as pathogenic. Functional studies demonstrated that this variant leads to cytoplasmic aggregation, reduced neurite outgrowth, and abnormal motor behavior in zebrafish. These results support the systematic use of functional assays to clarify the pathogenicity of uncertain variants, thereby improving diagnostic accuracy, preventing misdiagnosis, and enabling timely therapeutic interventions in ALS.

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