Genetic testing for non-parkinsonian movement disorders: Navigating the diagnostic maze

Abstract

Genetic testing has become a valuable diagnostic tool for movement disorders due to substantial advancements in understanding their genetic basis. However, the heterogeneity of movement disorders poses a significant challenge, with many genes implicated in different subtypes. This paper aims to provide a neurologist's perspective on approaching patients with hereditary hyperkinetic disorders with a focus on select forms of dystonia, paroxysmal dyskinesia, chorea, and ataxia. Age at onset, initial symptoms, and their severity, as well as the presence of any concurrent neurological and non-neurological features, contribute to the individual clinical profiles of hereditary non-parkinsonian movement disorders, aiding in the selection of appropriate genetic testing strategies. There are also more specific diagnostic clues that may facilitate the decision-making process and may be highly specific for certain conditions, such as diurnal fluctuations and l-dopa response in dopa-responsive dystonia, and triggering factors, duration and frequency of attacks in paroxysmal dyskinesia. While the genetic and mutational spectrum across non-parkinsonian movement disorders is broad, certain groups of diseases tend to be associated with specific types of pathogenic variants, such as repeat expansions in many of the ataxias. Some of these pathogenic variants cannot be detected by standard methods, such as panel or exome sequencing, but require the investigation of intronic regions for repeat expansions, such as Friedreich's or FGF14-linked ataxia. With our advancing knowledge of the genetic underpinnings of movement disorders, the incorporation of precise and personalized diagnostic strategies can enhance patient care, prognosis, and the application and development of targeted therapeutic interventions.

Keywords: Genetic testing; Hyperkinetic disorders; Non-parkinsonian disorders.