Nat. Rev. Neurol. doi:10.1038/nrneurol.2015.172 Figure 3 A guide to the clinical diagnosis of neurotransmitter disorders Figure 3 | A guide to the clinical diagnosis of neurotransmitter disorders. If red-flag clinical features of monoamine neurotransmitter disorders are present, the initial diagnostic approach should include careful history-taking and thorough clinical examination (including reviews of videos if available). Appropriate metabolite analysis could include blood glucose, lactate, ammonia, amino acids, biotinidase, thyroid function tests, acylcarnitine, carnitine profile, white-cell enzymes and very-long-chain fatty acids; urine amino acids, organic acids, oligosaccharides, purines and pyrimidines; CSF glucose, lactate, amino acids, and neurotransmitter profile. Skin and muscle biopsy can also be undertaken for specialist metabolic investigations. Specific patterns of neurotransmitter levels in the CSF patterns can indicate specific neurotransmitter disorders. Abbreviations: 5-HIAA, 5-hydroxyindoleacetic acid; AADC, aromatic L-amino acid decarboxylase; AD, autosomal dominant; AR, autosomal recessive; CSF, cerebrospinal fluid; DHPR, dihydropteridine reductase; DND, dopa-nonresponsive dystonia; DTDS, dopamine transporter deficiency syndrome; GTP-CH 1, GTP cyclohydrolase 1; HVA, homovanillic acid; MAO, monoamine oxidase; NBIA, neurodegeneration with brain iron accumulation; P-DE, pyroxidine-dependent epilepsy; PITX3, pituitary homeobox 3; PNPO, pyridoxamine 5′-phosphate oxidase; PTPS, 6-pyruvoyl tetrahydropterin synthase; RBC, red blood cell; SR, sepiapterin reductase; TH, tyrosine hydroxylase; VMAT2, vesicular monoamine transporter 2. Ng, J. et al. (2015) Monoamine neurotransmitter disorders—clinical advances and future perspectives Nat. Rev. Neurol. doi:10.1038/nrneurol.2015.172