An amyotrophic lateral sclerosis that is characterized by early childhood-onset lower extremity spasticity manifesting as toe walking and gait abnormalities, followed by progressive lower motor neuron-mediated weakness without sensory signs or symptoms and that has_material_basis_in heterozygous mutation in the SPTLC1 gene on chromosome 9q22. [ url:https://pubmed.ncbi.nlm.nih.gov/34059824/ ]