SELENOI and hereditary spastic paraplegia: Inactivation of the gene in mice is embryonic-lethal.The SELENOI mutation causes atrophy of the cerebellum and brainstem, which can cause sensorineural deafness, blindness, and seizures.Homozygous missense mutations in SELENOI correlate with seizure activity in some individuals of a pedigree with hereditary spastic paraplegia.