C9orf72-Linked Primary Lateral Sclerosis

Two brothers with a C9orf72 hexanucleotide repeat expansion develop frontotemporal dementia and unusually severe primary lateral sclerosis with acquired ocular motor apraxia and laryngeal dystonia. The report suggests primary lateral sclerosis may lie on the amyotrophic lateral sclerosis–frontotemporal dementia spectrum, and C9orf72 mutations may intensify eye-movement involvement beyond the motor system.