INTRODUCTION: Neurotransmitters are chemical messengers that enable communication between the neurons in the synaptic cleft. Inborn errors of neurotransmitter biosynthesis, breakdown and transport are a group of very rare neurometabolic diseases resulting in neurological impairment at any age from newborn to adulthood. METHODS AND RESULTS: The International Working Group on Neurotransmitter related Disorders (iNTD) is the first international network focusing on the study of primary and secondary neurotransmitter disorders. It was founded with the aim to foster exchange and improve knowledge in the field of these rare diseases. The newly established iNTD patient registry for neurotransmitter related diseases collects longitudinal data on the natural disease course, approach to diagnosis, therapeutic strategies, and quality of life of affected patients. The registry forms the evidence base for the development of consensus guidelines for patients with neurotransmitter related disorders. CONCLUSION: The iNTD network and registry will improve knowledge and strengthen research capacities in the field of inborn neurotransmitter disorders. The evidence-based guidelines will facilitate standardized diagnostic procedures and treatment approaches.

1st Department of Pediatrics Pediatric Neurology Unit Agia Sofia Hospital National and Kapodistrian University of Athens Athens Greece

Dep of Pediatrics 1st Faculty of Medicine Charles University Prague and General University Hospital Prague Prague Czech Republic

Department of Child Neurology Neurometabolic Unit CIBERER ISCIII Hospital Sant Joan de Déu Barcelona Spain

Department of Neurology and Child Neurology Radboudumc Nijmegen Donders Institute of Brain Cognition and Behaviour The Netherlands

Department of Neurology Washington University School of Medicine St Louis USA

Department of Neurosciences University of California San Diego Division of Neurology Rady Children's Hospital Rady Children's Institute Genomic Medicine San Diego USA

Department of Pediatric Neurology Reina Sofia University Hospital Maimonides Biomedical Research Institute of Cordoba University of Cordoba CIBERER ISCIII Cordoba Spain

Department of Pediatrics 1 Inherited Metabolic Disorders Medical University of Innsbruck Anichstrasse 35 6020 Innsbruck Austria

Department of Pediatrics and Child Neuropsychiatry Sapienza Università di Roma Rome Italy

Developmental Neurosciences UCL Institute of Child Health and Department of Neurology Great Ormond Street Hospital for Children NHS Foundations Trust London United Kingdom

Division of Biochemical Diseases BC Childrens Hospital Vancouver Canada

Division of Child Neurology and Metabolic Diseases University Children's Hospital Heidelberg Germany

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Insights into the expanding phenotypic spectrum of inherited disorders of biogenic amines

U-IMD: the first Unified European registry for inherited metabolic diseases

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies