Objective: To describe and analyze eye movements in patients with an inborn errors of metabolism

Background: Inborn errors of metabolism (IEMs) presenting in adults are still largely unexplored. Despite the fact that adult-onset phenotypes have been known for many years, little attention is given to these disorders in neurological training and daily practice. In the late-onset forms, movement disorders and psychiatric symptoms are often the presenting symptom. Abnormalities of eye movements are reported in specific IEMs, and can be an early presenting sign, but are easily overlooked in clinic. As far as we know, this is the first study that systematically analyzes eye movement disorders for different types of IEMs.

Method: We included 37 patients with 15 different IEMs. All patients underwent a standardized videotaped neurological examination and a video-oculography to analyze eye movements.

Results: Movement disorders were present in 30 of the 37 patients: dystonia (77%), ataxia (60%), and myoclonus (40%) were most frequent, and 14 patients had a history of psychiatric symptoms. Eye movement abnormalities were an early feature in at least 14 patients. Some of these abnormalities were specific for the type of IEM, including a vertical supranuclear gaze palsy in Niemann-Pick type C (n=10) and a progressive external ophthalmoplegia in mitochondrial disease (n=1). However, in the rest of the cases the abnormalities found on video-oculography were heterogeneous, even in patients with the same IEM. Eye movement abnormalities included saccadic occilations (70%), nystagmus (16%), abnormal saccades (52%), impaired smooth pursuit (73%), impaired optokinetic nystagmus (56%), and eye movement abnormalities during hyperventilation (32%). In addition, we detected for the first time eye movement disorders in patients with Krabbe disease, metochromatic leukodystrophy, and methylmalonic acidemia.

Conclusion: In adults with unexplained psychiatric symptoms or movement disorders, a special focus on examination of eye movements can serve as a relatively simple clinical tool to detect an IEM. We show that eye movement disorders may be present early in disease, not only in IEM known to be associated with eye movement disorders. However, with a few exceptions, the type of eye movement disorder does not point in the direction of specific IEM.

Videos of eye movement abnormalities are available to illustrate our findings.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/eye-movement-disorders-in-adolescents-and-adults-with-an-inborn-errors-of-metabolism/