Eye movement disorders in inborn errors of metabolism: A quantitative analysis of 37 patients

Inborn errors of metabolism are genetic disorders that need to be recognized as early as possible because treatment may be available. In late‐onset forms, core symptoms are movement disorders, psychiatric symptoms, and cognitive impairment. Eye movement disorders are considered to be frequent too, although specific knowledge is lacking. We describe and analyze eye movements in patients with an inborn error of metabolism, and see whether they can serve as an additional clue in the diagnosis of particularly late‐onset inborn errors of metabolism. Demographics, disease characteristics, and treatment data were collected. All patients underwent a standardized videotaped neurological examination and a video‐oculography. Videos are included. We included 37 patients with 15 different inborn errors of metabolism, including 18 patients with a late‐onset form. With the exception of vertical supranuclear gaze palsy in Niemann‐Pick type C and external ophthalmolplegia in Kearns‐Sayre syndrome, no relation was found between the type of eye movement disorder and the underlying metabolic disorder. Movement disorders were present in 29 patients (78%), psychiatric symptoms in 14 (38%), and cognitive deficits in 26 patients (70%). In 87% of the patients with late‐onset disease, eye movement disorders were combined with one or more of these core symptoms. To conclude, eye movement disorders are present in different types of inborn errors of metabolism, but are often not specific to the underlying disorder. However, the combination of eye movement disorders with movement disorders, psychiatric symptoms, or cognitive deficits can serve as a diagnostic clue for an underlying late‐onset inborn error of metabolism.