The first nonsense mutation in alsin results in a homogeneous phenotype of infantile-onset ascending spastic paralysis with bulbar involvement in two siblings.

Eight mutations in the ALS2 gene have been described as causing autosomal-recessive juvenile-onset forms of the motor neuron diseases amyotrophic lateral sclerosis, primary lateral sclerosis and hereditary spastic paraplegia. All mutations are small deletions that are predicted to result in a frameshift and premature truncation of the alsin protein. Here we describe a ninth ALS2 mutation, in two siblings affected by infantile-onset ascending spastic paraplegia with bulbar involvement. This mutation is predicted to result in the substitution of an amino acid by a stop codon, and thus is the first nonsense mutation detected in this gene. It is probable that full-length alsin is required for the proper development and/or functioning of upper motor neurons.