Vertical nystagmus most often signifies acquired disease, but occasionally it may be present without symptoms and without any obvious neurologic disorder, and very rarely it may be inherited. Three families with hereditary motor-type vertical (and horizontal) nystagmus and mild ataxia are described. Most of the affected individuals also showed absent optokinetic nystagmus and a hyperactive vestibulo-ocular response. Only two similar families have been reported previously.
Marmor MF. Hereditary Vertical Nystagmus. Arch Ophthalmol. 1973;90(2):107-111. doi:10.1001/archopht.1973.01000050109007