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serum/urine melatonin, urinary dopamine and plasma amino-acid ratios.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Urinary dopamine and melatonin are surrogate readouts, not a direct demonstration of restored brain neurotransmitter concentrations.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"L-Phenylalanine collection; species, compartment, exposure, co-substrates and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"l-phenylalanine","display_name":"L-Phenylalanine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"A downstream marker can improve even when phenylalanine concentration stays similar.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Large neutral amino acid supplementation increases melatonin synthesis in phenylketonuria: a new biomarker. · 2013 · https://pubmed.ncbi.nlm.nih.gov/23164313/ · DOI 10.1016/j.jpeds.2012.10.015","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"9afc56f6-7777-5626-adb0-e5e628b17bc7","evidence_kind":"source_excerpt","locator":"Lines 214-220","start_line":214,"end_line":220,"excerpt":"## l-phenylalanine-lnaa-monoamine-markers\nA downstream marker can improve even when phenylalanine concentration stays similar.\nIn ten adults with PKU, LNAA supplementation increased melatonin measures and urinary dopamine while phenylalanine itself did not significantly change.\nModel: Three three-week crossover periods; serum/urine melatonin, urinary dopamine and plasma amino-acid ratios.\nLimitations: Urinary dopamine and melatonin are surrogate readouts, not a direct demonstration of restored brain neurotransmitter concentrations.\nEvidence access: Primary full text\nLarge neutral amino acid supplementation increases melatonin synthesis in phenylketonuria: a new biomarker. · 2013 · https://pubmed.ncbi.nlm.nih.gov/23164313/ · DOI 10.1016/j.jpeds.2012.10.015","model_system":"Three three-week crossover periods; serum/urine melatonin, urinary dopamine and plasma amino-acid ratios.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access and experimental limitations specified.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"54de7c56-1e60-5d7b-8ef9-852c58ae92ba","stable_key":"import-56f1d914-e7da-595a-af69-c217b2b47407","title":"L-Phenylalanine: transport, protein synthesis, cofactor recycling and cross-nutrient mechanisms (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted research curation; 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