Teaching Video NeuroImage: Infantile Upbeat Nystagmus as an Isolated Presentation of CACNA1F -Related Retinal Dystrophy

A healthy ex-full term 2-month-old male infant with unremarkable birth history presented with frequent upbeat jerk nystagmus (Video 1).He did not reliably track or blink to threat and showed no response to optokinetic drum.The remainder of the neuro-ophthalmological examination, including fundoscopy, was normal.Upbeat nystagmus may localize to the brainstem and/or cerebellar vermis, but brain MRI was normal.Complete blood count, metabolic profile, vitamin B12, vitamin B1, and toxicology were normal.Trio exome sequencing revealed a pathogenic, X-linked hemizygous variant c.3436C>T p.(Gln1146Ter) in CACNA1F, diagnostic of CACNA1F-related retinal dystrophy.In this disorder, defective voltage-gated L-type calcium channels in rod photoreceptors disrupt phototransduction to retinal bipolar cells, leading to oscillatory entrainment in the vestibulo-ocular and optokinetic reflex loop subserving congenital nystagmus. 1While patients with CACNA1F-related retinal dystrophy variably present with decreased visual acuity, myopia, and nystagmus, prognosis is fair and limited to deficits in vision.Nystagmus may improve with age.