Tryptophan
| Evidence Level: L3 | Predicted Indications: 8 |
Table of Contents
Tryptophan: From Maple Syrup Urine Disease to Restless Legs Syndrome
One-Sentence Summary
Tryptophan (marketed as Maapliv) was originally authorised in the EU for acute decompensation episodes of maple syrup urine disease (MSUD). The TxGNN model predicts it may be effective for Restless Legs Syndrome, but there are no registered clinical trials and only 6 publications, mostly older or indirect, supporting this direction.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Maple syrup urine disease (MSUD) presenting with an acute decompensation episode, in patients from birth who are not eligible for an oral or enteral BCAA-free formulation |
| Predicted New Indication | Restless legs syndrome |
| TxGNN Prediction Score | 99.72% |
| Evidence Level | L3 |
| EU Market Status | Cancelled only (no currently valid authorisation) |
| Number of Authorizations | 1 (cancelled) |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available. Based on known information, tryptophan is an essential amino acid and the precursor of serotonin and melatonin. Its authorised use is in the metabolic disease MSUD, where it is part of an amino acid-based therapy, and mechanistically it may be applicable to RLS through its effects on neurotransmitter pathways.
The link to restless legs syndrome rests on the idea that serotonergic and dopaminergic signalling are involved in RLS and periodic limb movements. Small clinical reports from 1986–1987 examined L-tryptophan in RLS and periodic leg movements. Pharmacovigilance data also show that serotonergic antidepressants can worsen movement disorders, so the serotonergic system is clearly relevant, but the direction of effect is not straightforward.
The original indication (a metabolic disorder) and RLS are not closely related clinically. The prediction is therefore a hypothesis-generating signal, not a confirmed therapeutic link.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 3953904 | 1986 | Clinical study | Am J Psychiatry | L-tryptophan in the treatment of RLS (no abstract available) |
| 3659737 | 1987 | Clinical study | Sleep | Periodic leg movement with L-dopa, 5-hydroxytryptophan and L-tryptophan (no abstract available) |
| 33836477 | 2021 | Systematic review / meta-analysis | Sleep Med Rev | RLS in chronic liver disease; elevated tryptophan is among the proposed contributing factors |
| 1305630 | 1992 | Review | Int J Neurosci | L-tryptophan in neuropsychiatric disorders, including movement disorders |
| 36897462 | 2023 | Case series | Neurol Sci | RLS in DNAJC12 deficiency, with impaired dopaminergic and serotonergic neurotransmission |
| 32546134 | 2020 | Pharmacovigilance study | BMC Psychiatry | Antidepressants and movement disorders; shows the serotonergic system matters in both directions |
EU Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| EMEA/H/C/005557 (cancelled) | Maapliv | Not specified | Maple syrup urine disease (MSUD) presenting with an acute decompensation episode in patients from birth who are not eligible for an oral and enteral… |
Safety Considerations
- Contraindication signals from the knowledge graph (not label text): autoimmune disease, systemic lupus erythematosus (including paediatric), anxiety disorder, neurotic disorder, dysthymic disorder, schizophrenia, phenylketonuria and other disorders of phenylalanine metabolism, and eosinophilia-myalgia syndrome (including the form associated with tryptophan). The eosinophilia-myalgia syndrome link reflects a historical outbreak linked to contaminated L-tryptophan supplements.
- Drug Interactions: 17 interactions were identified.
- Major (10): lorcaserin, dolasetron, palonosetron, ondansetron, fenfluramine, granisetron, sibutramine, methylene blue, doxepin (including topical), procarbazine. Many of these involve serotonergic effects, so serotonin syndrome is a key concern.
- Moderate (7): morphine, codeine, hydrocodone, cyproheptadine, ozanimod, ifosfamide.
Please refer to the SmPC for official warnings and contraindications.
Conclusion and Next Steps
Decision: Hold
Rationale: The RLS prediction has a very high model score, but the supporting evidence is limited to two small, dated clinical reports (1986–1987), with no registered trials. The product’s EU authorisation is cancelled. Many serotonergic drug interactions, and the history of eosinophilia-myalgia syndrome, call for caution. At best this is a research question.
To proceed, the following is needed:
- Full text and critical appraisal of the 1986–1987 clinical studies, as no abstracts were available
- A modern, controlled trial design for tryptophan in RLS
- Mechanism of action data
- SmPC warnings and contraindications (the package insert is not yet parsed)
- Confirmation of product quality and purity requirements, given the eosinophilia-myalgia syndrome history
- A plan for managing serotonergic drug interactions
- Clarification of why the authorisation was cancelled and what formulation would be used for RLS (route and dosage form compatibility not yet assessed)
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.