Although juvenile ALS is defined by onset of upper and lower motor neuron degeneration and related symptoms before 25 years of age, SPTLC1 and SPTLC2-associated ALS together form a distinct, early childhood onset subgroup of neurodevelopmental motor neuron disease with typical onset of disease in the first few years of life. This evidence concerns the gene SPTLC1 and amyotrophic lateral sclerosis.