SOD1 mutations in Taiwanese ALS patients: Clinical characteristics, frequency, and a p.T138R founder effect

Mutations in SOD1 are a well-established genetic cause of amyotrophic lateral sclerosis (ALS), exerting toxic gain-of-function effects that promote protein misfolding and aggregation in motor neurons and glial cells. The emergence of SOD1-targeted antisense oligonucleotide therapy underscores the clinical importance of precise genetic diagnosis. This study aimed to determine the frequency, clinical characteristics, and potential founder effect of SOD1 mutations in a large Taiwanese ALS cohort, and to evaluate their aggregation propensity in vitro.

All coding exons of SOD1 were analyzed by Sanger sequencing in 650 unrelated Taiwanese patients with ALS. Haplotype analysis using single nucleotide polymorphism markers flanking SOD1 was conducted to assess a potential founder effect. Protein cross-linking assays were performed to assess the aggregation propensity of 11 SOD1 variants.

Seventeen pathogenic SOD1 variants were identified in 26 probands and 12 affected relatives. Mean age at onset was 48.9 ± 14.9 years, and 8% had bulbar-onset ALS. The most frequent variant was p.T138R (8 probands), followed by p.G11A (3 probands). The other 15 variants each occurred in a single family. A shared ancestral haplotype was observed among p.T138R carriers. Cross-linking experiments demonstrated oligomer formation in all tested mutant SOD1 proteins compared to the wild-type protein, supporting their pathogenicity.

SOD1 mutations account for approximately 4% of ALS cases in Taiwan, are associated with earlier onset and predominantly spinal-onset ALS, and include a p.T138R founder variant. These findings highlight the importance of genetic screening in ALS, particularly in guiding eligibility for emerging targeted therapies.