Inherited disorders of neurotransmitter metabolism are rare neurodevelopmental diseases presenting with movement disorders and global developmental delay. This study presents the results of the first standardized deep phenotyping approach and describes the clinical and biochemical presentation at disease onset as well as diagnostic approaches of 275 patients from the registry of the International Working Group on Neurotransmitter related Disorders. The results reveal an increased rate of prematurity, a high risk for being small for gestational age and for congenital microcephaly in some disorders. Age at diagnosis and the diagnostic delay are influenced by the diagnostic methods applied and by disease-specific symptoms. The timepoint of investigation was also a significant factor: delay to diagnosis has decreased in recent years, possibly due to novel diagnostic approaches or raised awareness. Although each disorder has a specific biochemical pattern, we observed confounding exceptions to the rule. The data provide comprehensive insights into the phenotypic spectrum of neurotransmitter disorders.We thank all patients and their families for their contributions to this study and for their trust. T.H. and J.K. were supported the grant from the Ministry of Health of the Czech Republic RVO-VFN 64165 GJIH-0599-00-7-846 and ProgresQ26/LF1. A.G.C. and N.J.P. are supported by FIS P118/00111 “Instituto de Salud Carlos III (ISCIII)” and “Fondo Europeo de desarrollo regional (FEDER)”. T.O., K.J., G.F.H. and O.K.H. were supported in parts by the Dietmar Hopp Foundation, St. Leon-Rot, Germany. M.A.K. is funded by an NIHR Professorship, the Sir Jules Thorn Award for Biomedical Research and the Rosetrees trust. M.V. is supported by Stichting Stofwisselkracht Grant. D.H. acknowledges funding by the Molecular Diagnostics Program of the National Center for Tumor Diseases (NCT) Heidelberg.Peer reviewe
