Movement disorders in neuro-metabolic diseases

Abstract

Inborn errors of metabolism (IEM) are a group of genetic disorders characterized by dysfunction of an enzyme or other protein involved in cellular metabolism. 1 Most IEMs involve the nervous system (neuro-metabolic diseases or NMD). NMD often present with a complex clinical picture: psychomotor retardation and/or regression, pyramidal signs, ataxia, hypotonia and epilepsy and movement disorders. 1 Movement disorders are more frequently part of this complex picture than a predominant symptom, however in some instances the clinical picture may be summarized in an invalidating movement disorder. 2 On a phenomenology basis, one can distinguish eight main types of movement disorders: dystonia and athetosis, chorea, tremor with or without parkinsonism, ballismus, myoclonus, tics and stereotypies. Most of these abnormal involuntary movements generate from a dysfunction or a lesion in the basal ganglia, excepting myoclonus, the origin of which can vary (cortical, brainstem, basal ganglia, spinal and even peripheral nervous system). 3 Classically the most frequently observed movement disorders in NMD are: dystonia, myoclonus, chorea, tremor and parkinsonism ( Fig. 1). The primary goal of this article is, departing from the literature and a large personal series, to describe the types of movement disorders most frequently observed in NMD and to discuss their clinical value in the setting of specific types of NMD.