Eye movement disorders in genetic dystonia syndromes: A literature overview

With the growing possibilities in genetic testing, the number of genetic disorders associated with dystonia has constantly increased over the last few years. Accurate phenotyping is crucial to guide and interpret genetic analyses in the search for an etiological diagnosis. Although eye movements examination has proven a valuable tool in the assessment of patients with inherited movement disorders such as ataxia or parkinsonism, less is known about the association between eye movement disorders and genetic dystonia. This study aimed to summarize the most frequent eye movement disorders in monogenetic forms of dystonia as classified by the Movement Disorders Society (MDS). More than sixty genetic disorders causing dystonia were repeatedly associated with eye movement disorders. Among these, 24 are classified as DYT genes, 22 were classified by MDS as having another prominent movement disorder, and 19 are genetic disorders that manifest with dystonia but are not included in the MDS classification. Six different eye movement disorders have consistently been reported (saccadic slowing and supranuclear gaze palsy, saccadic initiation failure and oculomotor apraxia, saccadic dysmetria, oculogyric crisis, nystagmus and ophthalmoplegia). The phenotypic association of each disorder with monogenic dystonic diseases, as well as the possible underlying pathophysiological mechanisms, is described here. Our findings suggest that eye movement disorders, along with the movement phenotype, may help delineate subgroups of dystonia by reflecting disruptions in specific brain networks. Therefore, eye movement examination is a crucial part of the neurological evaluation, providing valuable insights into patients with inherited forms of dystonia.