Patients with Allan-Herndon-Dudley Syndrome (MCT8 Deficiency) Display Symptoms of Parkinsonism in Childhood and Respond to Levodopa/Carbidopa Treatment

Abstract

Background: Patients with mutations in the monocarboxylate transporter 8 (MCT8, SLC16A2) suffer from X-linked recessive Allan-Herndon-Dudley syndrome (AHDS), which is characterized by developmental delay and a severe movement disorder. Current trials using thyroid hormone derivatives to overcome the transporter defect have failed to achieve patient-oriented therapeutic goals. Objectives: Our aim was to define the type of movement disorder in AHDS in an observational cohort study and to investigate the causative role of the dopaminergic system. Methods: We present longitudinal clinical data from the DEEPTYPE registry of 11 patients with video documentation, standardized phenotyping, cerebrospinal fluid (CSF) analysis, neuroimaging data, and the treatment response to levodopa/carbidopa supplementation. Results: Children presented with signs of childhood parkinsonism, including hypokinesia, hypomimia, inability to sit or stand, rigidity, dystonia, and autonomic dysfunction. CSF homovanillic acid concentrations were decreased (n = 12), suggesting an isolated dopamine pathway impairment. Seven out of 8 patients responded favorably to l-dopa/carbidopa supplementation and we did not observe any adverse drug reactions. Conclusions: AHDS is associated with childhood parkinsonism, which is linked with biochemical abnormalities of dopamine metabolism. It can be treated with l-dopa/carbidopa supplementation. However, further research is needed to elucidate the exact effect of MCT8 deficiency on dopamine metabolism. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.