{
  "slug": "pku-phenylalanine",
  "title": "Phenylalanine accumulation in PAH deficiency",
  "claim": "Sustained marked phenylalanine elevation caused by PAH-deficient phenylketonuria is a major cause of developmental intellectual disability, which can be prevented by early, sustained, nutritionally adequate dietary phenylalanine restriction.",
  "update_date": "2026-10-05",
  "search_cutoff": "2026-10-05",
  "framework_for_addendum": "HSEF v5.3 causal distinctions",
  "historical_scorecard_schema": "5.4",
  "regraded": false,
  "status": "curated_local_addendum",
  "full_academic_review_complete": false,
  "summary": "Early exposure and early treatment support phenylalanine-related developmental injury in PKU. Adult challenge experiments, brain transport and discordant untreated outcomes refine vulnerability and reversibility; biochemical lowering and neurocognitive recovery remain separate endpoints.",
  "timeline": [
    {
      "year": "1953",
      "source_id": "P13098090",
      "design": "Historical dietary report",
      "finding": "An early report examined phenylalanine intake in PKU.",
      "limit": "Metadata-only historical anchor: outcome details were not independently re-examined in this update.",
      "historical_anchor_only": true
    },
    {
      "year": "1974",
      "source_id": "P4140266",
      "design": "Affected-sibling comparison",
      "finding": "Earlier treatment was associated with better intellectual outcomes.",
      "limit": "Nonrandomized developmental treatment comparison; family and timing factors require attention.",
      "historical_anchor_only": false
    },
    {
      "year": "1998",
      "source_id": "P9809507",
      "design": "Brain spectroscopy and phenylalanine challenge",
      "finding": "Brain transport varied among patients with different clinical vulnerability.",
      "limit": "Small selected sample does not explain all preserved untreated cognition.",
      "historical_anchor_only": false
    },
    {
      "year": "1999",
      "source_id": "P10207169",
      "design": "Human LNAA/phenylalanine challenge",
      "finding": "Other large neutral amino acids blocked brain phenylalanine influx and EEG slowing.",
      "limit": "Acute transport and EEG effects do not establish long-term cognitive recovery.",
      "historical_anchor_only": false
    },
    {
      "year": "2007",
      "source_id": "P17693179",
      "design": "Sapropterin randomized trial",
      "finding": "Responsive patients had lower blood phenylalanine on treatment.",
      "limit": "Blood lowering is not itself a hard neurocognitive outcome.",
      "historical_anchor_only": false
    },
    {
      "year": "2010",
      "source_id": "P21153445",
      "design": "Adult randomized crossover challenge",
      "finding": "Higher phenylalanine impaired sustained attention and mood in the tested adults.",
      "limit": "Short challenge in early-treated adults does not measure irreversible childhood injury.",
      "historical_anchor_only": false
    },
    {
      "year": "2017",
      "source_id": "P29331172",
      "design": "Adult phenylketonuric-mouse intervention",
      "finding": "Blood lowering corrected monoamine deficits and partly improved behaviour.",
      "limit": "Adult biochemical rescue did not reverse all developmental cognitive deficits.",
      "historical_anchor_only": false
    },
    {
      "year": "2018",
      "source_id": "P29628378",
      "design": "Pegvaliase randomized discontinuation",
      "finding": "Continuation maintained lower blood phenylalanine than discontinuation.",
      "limit": "An enriched withdrawal design tests maintenance, not untreated developmental causation.",
      "historical_anchor_only": false
    },
    {
      "year": "2024",
      "source_id": "P38569786",
      "design": "Four-week adult randomized challenge",
      "finding": "Working-memory accuracy met the noninferiority criterion, while sustained attention differed.",
      "limit": "Domain-specific and short-term outcomes do not justify a general claim that high phenylalanine is harmless.",
      "historical_anchor_only": false
    },
    {
      "year": "2026",
      "source_id": "P41853686",
      "design": "Untreated adult-sister case comparison",
      "finding": "Sisters had strikingly different cognitive outcomes despite similar tested biochemical/genetic features.",
      "limit": "A rare discordant pair identifies an unresolved modifier rather than reversing population-level causation.",
      "historical_anchor_only": false
    }
  ],
  "gaps": [
    {
      "id": "G1",
      "question": "What determines individual brain exposure and vulnerability?",
      "source_ids": [
        "P9809507",
        "P10207169",
        "P41853686"
      ],
      "alternative": "Blood phenylalanine may imperfectly reflect transport, protective modifiers or prior developmental exposure.",
      "discriminating_test": "Longitudinal brain spectroscopy, genotype and exposure histories in prospectively identified discordant cases; matched ascertainment and independent replication.",
      "gap_type": "bounded_causal_uncertainty",
      "interpretation": "An unresolved inference or scope limit in the checked evidence, not a claim that no relevant study exists anywhere."
    },
    {
      "id": "G2",
      "question": "Which adult domains change reversibly over which time scale?",
      "source_ids": [
        "P21153445",
        "P38569786",
        "P29331172"
      ],
      "alternative": "Attention, mood and working memory may differ in sensitivity and recovery.",
      "discriminating_test": "Longer controlled exposure/reduction studies with prespecified domains, washout and repeated brain measures; distinguish early-treated adults from developmental injury.",
      "gap_type": "bounded_causal_uncertainty",
      "interpretation": "An unresolved inference or scope limit in the checked evidence, not a claim that no relevant study exists anywhere."
    },
    {
      "id": "G3",
      "question": "Which mediator carries developmental versus adult effects?",
      "source_ids": [
        "P10207169",
        "P29331172",
        "P4140266"
      ],
      "alternative": "Transport competition, monoamine inhibition and developmental structural effects may have different roles.",
      "discriminating_test": "Age-stratified model blockade/rescue and human mediator measurement; require outcomes beyond blood phenylalanine and avoid attributing every effect to one pathway.",
      "gap_type": "bounded_causal_uncertainty",
      "interpretation": "An unresolved inference or scope limit in the checked evidence, not a claim that no relevant study exists anywhere."
    },
    {
      "id": "G4",
      "question": "Do newer lowering strategies improve durable neurocognitive outcomes?",
      "source_ids": [
        "P17693179",
        "P29628378",
        "P21153445"
      ],
      "alternative": "A biochemical response may leave previous damage or adherence-related fluctuations unchanged.",
      "discriminating_test": "Prospective comparative follow-up with cognition, function, exposure variability and adverse events; separate responder-enriched maintenance from initiation trials.",
      "gap_type": "bounded_causal_uncertainty",
      "interpretation": "An unresolved inference or scope limit in the checked evidence, not a claim that no relevant study exists anywhere."
    }
  ],
  "source_cards": [
    {
      "id": "P13098090",
      "pmid": "13098090",
      "doi": "10.1016/s0140-6736(53)90473-5",
      "title": "Influence of phenylalanine intake on phenylketonuria.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/13098090/",
      "issue_year": "1953",
      "electronic_date": "",
      "access_depth": "metadata_only",
      "checked_details": "Identifier, title and publication metadata checked; original results not re-examined.",
      "publication_types": [
        "Journal Article"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "full_text_complete",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P4140266",
      "pmid": "4140266",
      "doi": "10.1016/s0140-6736(74)91873-x",
      "title": "Natural history of phenylketonuria and influence of early treatment.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/4140266/",
      "issue_year": "1974",
      "electronic_date": "",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Journal Article"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P9809507",
      "pmid": "9809507",
      "doi": "10.1097/00004647-199811000-00004",
      "title": "Blood-brain barrier phenylalanine transport and individual vulnerability in phenylketonuria.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/9809507/",
      "issue_year": "1998",
      "electronic_date": "",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Journal Article",
        "Research Support, Non-U.S. Gov't"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P10207169",
      "pmid": "10207169",
      "doi": "10.1172/JCI5017",
      "title": "Large neutral amino acids block phenylalanine transport into brain tissue in patients with phenylketonuria.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/10207169/",
      "issue_year": "1999",
      "electronic_date": "",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Journal Article",
        "Research Support, Non-U.S. Gov't"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "full_text_partial",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P17693179",
      "pmid": "17693179",
      "doi": "10.1016/S0140-6736(07)61234-3",
      "title": "Efficacy of sapropterin dihydrochloride (tetrahydrobiopterin, 6R-BH4) for reduction of phenylalanine concentration in patients with phenylketonuria: a phase III randomised placebo-controlled study.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/17693179/",
      "issue_year": "2007",
      "electronic_date": "",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Clinical Trial, Phase III",
        "Journal Article",
        "Multicenter Study",
        "Randomized Controlled Trial",
        "Research Support, N.I.H., Extramural",
        "Research Support, Non-U.S. Gov't"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P21153445",
      "pmid": "21153445",
      "doi": "10.1007/s10545-010-9253-9",
      "title": "High phenylalanine levels directly affect mood and sustained attention in adults with phenylketonuria: a randomised, double-blind, placebo-controlled, crossover trial.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/21153445/",
      "issue_year": "2011",
      "electronic_date": "2010-12-10",
      "access_depth": "full_text_partial",
      "checked_details": "Results: washout was at least four weeks and phenylalanine approached baseline before the second period. Adult challenge outcomes do not test fixed childhood injury.",
      "publication_types": [
        "Journal Article",
        "Randomized Controlled Trial"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P29331172",
      "pmid": "29331172",
      "doi": "10.1016/j.ymgme.2017.10.009",
      "title": "Blood phenylalanine reduction corrects CNS dopamine and serotonin deficiencies and partially improves behavioral performance in adult phenylketonuric mice.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/29331172/",
      "issue_year": "2018",
      "electronic_date": "2017-10-19",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Journal Article",
        "Research Support, N.I.H., Extramural"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P29628378",
      "pmid": "29628378",
      "doi": "10.1016/j.ymgme.2018.03.003",
      "title": "Pegvaliase for the treatment of phenylketonuria: A pivotal, double-blind randomized discontinuation Phase 3 clinical trial.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/29628378/",
      "issue_year": "2018",
      "electronic_date": "2018-03-18",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Clinical Trial, Phase III",
        "Journal Article",
        "Randomized Controlled Trial",
        "Research Support, Non-U.S. Gov't"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "full_text_partial",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P38569786",
      "pmid": "38569786",
      "doi": "10.1016/j.ajcnut.2023.11.007",
      "title": "Cognition after a 4-week high phenylalanine intake in adults with phenylketonuria - a randomized controlled trial.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/38569786/",
      "issue_year": "2024",
      "electronic_date": "2024-02-09",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Randomized Controlled Trial",
        "Journal Article",
        "Research Support, Non-U.S. Gov't"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "abstract_metadata",
      "complete_paper_examined_in_this_update": false
    },
    {
      "id": "P41853686",
      "pmid": "41853686",
      "doi": "10.1016/j.ymgmr.2026.101304",
      "title": "Two adult sisters with untreated phenylketonuria: Strikingly discordant clinical phenotype.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/41853686/",
      "issue_year": "2026",
      "electronic_date": "2026-03-07",
      "access_depth": "abstract_excerpt_checked",
      "checked_details": "Primary record and selected abstract passages checked; no complete-paper appraisal credited.",
      "publication_types": [
        "Journal Article"
      ],
      "correction_notices": [],
      "cohort_note": "No independence claim made; cohort identity beyond the cited report was not exhaustively audited.",
      "baseline_access_depth": "full_text_complete",
      "complete_paper_examined_in_this_update": false
    }
  ],
  "access_counts": {
    "full_text_partial": 1,
    "abstract_excerpt_checked": 8,
    "metadata_only": 1
  },
  "browser_messages": 2,
  "targeted_check": {
    "pmid": "21153445",
    "provider_access": "selected primary full-text passages reported by Consensus",
    "independent_primary_body_crosscheck": true,
    "verification_scope": "Results: washout was at least four weeks and phenylalanine approached baseline before the second period. Adult challenge outcomes do not test fixed childhood injury."
  },
  "editorial_warning": "",
  "reading_limit": "This focused addendum does not establish 50–70 complete primary Methods/Results examinations per review. Baseline reading receipts and scores retain their original scope.",
  "method": "Case-specific Consensus records assisted gap discovery, chronology and targeted paper questions. Shared template wording about an amyloid-specific Deep follow-up is not evidence of a Deep run for this topic; the dated source records establish the actual use and access limits. Primary identifiers, selected abstract passages, correction notices and available primary-body passages were cross-checked. Generated absence cells, duplicate milestones and unsupported access claims were rejected."
}