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Primary Carnitine Deficiency

Disease Pathophysiology Research Template

2026-02-23
Falcon MONDO:0008919 Model: Edison Scientific Literature 45 citations

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Pathophysiology Research Template

Target Disease

  • Disease Name: Primary Carnitine Deficiency
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Primary Carnitine Deficiency. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

  • What are the primary pathophysiological mechanisms?
  • What molecular pathways are dysregulated?
  • What cellular processes are affected?

2. Key Molecular Players

  • Genes/Proteins: Which genes are causally involved or implicated?
  • Chemical Entities: What metabolites, drugs, or small molecules are relevant?
  • Cell Types: Which cell types are primarily affected?
  • Anatomical Locations: Which tissues/organs are involved?

3. Biological Processes (for GO annotation)

  • What biological processes (GO terms) are disrupted?
  • Consider: signaling pathways, metabolic processes, cellular responses, transport, etc.

4. Cellular Components

  • Where in the cell do key processes occur?
  • Consider: organelles, membrane compartments, extracellular space, etc.

5. Disease Progression

  • What is the sequence of events from initial trigger to clinical manifestation?
  • Are there distinct stages or phases?

6. Phenotypic Manifestations

  • What are the key clinical phenotypes?
  • How do they relate to the underlying mechanisms?

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes where possible to support key statements

Output Format

Structure your response as a narrative that could be used to populate a disease knowledge base entry with: - Pathophysiology description - Gene/protein annotations with ontology terms (HGNC, GO) - Phenotype associations (HP terms) - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Evidence items with PMIDs

Title: Pathophysiology of Primary Carnitine Deficiency (PCD; systemic primary carnitine deficiency / carnitine uptake defect) Publication date: 2026-02-24

Key sources prioritized (2023–2024) 1) Yin et al., Heliyon, 2024-07. https://doi.org/10.1016/j.heliyon.2024.e33581 (yin2024unravelingcardiomyocyteresponses pages 1-2) 2) Zhou et al., Orphanet J Rare Dis, 2024-07. https://doi.org/10.1186/s13023-024-03267-x (zhou2024screeningprimarycarnitine pages 1-2) 3) Galluccio et al., Int J Mol Sci, 2024-08. https://doi.org/10.3390/ijms25168743 (galluccio2024thehumanoctn pages 6-9) 4) Pochini et al., Biomolecules, 2024-03. https://doi.org/10.3390/biom14040392 (pochini2024inflammationandorganic pages 3-5) 5) Lefèvre et al., Int J Neonatal Screening, 2023-02. https://doi.org/10.3390/ijns9010006 (lefevre2023newbornscreeningof pages 1-2) 6) Lin et al., Mol Genet Genomic Med, 2024-09. https://doi.org/10.1002/mgg3.70003 (lin2024incorporatingnext‐generationsequencing pages 1-2)

  1. Key concepts and definitions (current understanding)

Disease definition and causal mechanism Primary carnitine deficiency (PCD) is an autosomal recessive disorder caused by loss-of-function variants in SLC22A5, encoding the high-affinity sodium-dependent carnitine transporter OCTN2. Defective OCTN2 leads to impaired cellular uptake and impaired renal tubular reabsorption of carnitine, causing systemic and intracellular carnitine depletion and impaired mitochondrial long-chain fatty-acid β-oxidation. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2)

Core biochemical concept (“carnitine shuttle” function) Carnitine is required for the mitochondrial handling of long-chain fatty acids: impaired OCTN2 function causes low intracellular carnitine that “hindering the β-oxidation of fatty acids,” thereby particularly affecting tissues that rely heavily on fatty-acid oxidation for ATP, such as heart and skeletal muscle. (yin2024unravelingcardiomyocyteresponses pages 1-2)

Phenotypic spectrum Recent clinical syntheses highlight a bimodal presentation: (i) acute metabolic decompensation in infancy (e.g., hypoketotic hypoglycemia, hyperammonemia, liver dysfunction/encephalopathy), and (ii) a more insidious cardiomyopathy phenotype (dilated or hypertrophic, with heart failure/arrhythmia risk) often accompanied by skeletal muscle myopathy. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2, jolfayi2024anovelpathogenic pages 1-2)

  1. Core pathophysiology (molecular and cellular mechanisms)

2.1 Primary pathophysiological mechanisms A) Transport defect → systemic/intracellular carnitine depletion OCTN2 dysfunction reduces carnitine uptake from blood and gut and reduces renal carnitine reabsorption, producing low plasma free carnitine and tissue depletion; urinary “carnitine wasting” is repeatedly emphasized as a central mechanism. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2, kheirandish2024theroleof pages 4-5)

B) Carnitine depletion → impaired mitochondrial long-chain fatty-acid β-oxidation Low intracellular carnitine decreases the ability to oxidize long-chain fatty acids and generate energy, contributing to energy failure, especially in myocardium and skeletal muscle. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2, kheirandish2024theroleof pages 7-8)

C) Energy stress and lipotoxicity → organ dysfunction Clinical and mechanistic descriptions link carnitine depletion and impaired fatty-acid oxidation to cardiomyopathy, skeletal muscle weakness, liver involvement, and susceptibility to metabolic crises with fasting. (yin2024unravelingcardiomyocyteresponses pages 1-2, kheirandish2024theroleof pages 5-7, kheirandish2024theroleof pages 7-8)

2.2 Dysregulated pathways and cellular processes (from 2024 single-nucleus cardiac transcriptomics) A 2024 single-nucleus RNA-seq study of OCTN2-deficient mouse hearts (N32S point mutation and knockout) identifies multiple downstream cellular programs and altered intercellular signaling:

• Contractile and calcium-handling gene program suppression: genes “with cardiac contraction were significantly downregulated in the OCTN2-deficient group,” including MYH7, TNNI3, TNNT2, ACTC1, TPM1, and RYR2. (yin2024unravelingcardiomyocyteresponses pages 8-9)

• Fibrosis and extracellular matrix (ECM) remodeling: the authors frame fibrosis as “Excessive extracellular matrix (ECM) protein and epithelial-mesenchymal transition (EMT)” with increases in fibrosis-associated genes (e.g., FN1, COL1A2, POSTN, ACTA2) and increased fibroblast abundance (“The number of fibroblasts significantly increased in the OCTN2-deficient group.”). (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15)

• Pro-fibrotic macrophage–fibroblast/cardiomyocyte crosstalk: macrophage SPP1 is elevated and macrophage-to-cardiomyocyte communication is enhanced; the authors note “Macrophages-derived secreted phosphoprotein 1 (SPP1) promotes the activation of fibroblasts.” (yin2024unravelingcardiomyocyteresponses pages 1-2, yin2024unravelingcardiomyocyteresponses pages 11-13)

• GAS6-centered signaling and fibrosis initiation: “GAS6 gene significantly contributes to the initiation of myocardial fibrosis,” with “GAS6 serves as a trigger for myocardial fibrosis by inducing EMT through the GAS6/AXL pathway and enhancing macrophage regulation via the GAS6/MERTK pathway.” (yin2024unravelingcardiomyocyteresponses pages 13-15)

• Developmental transcription factor downregulation: cardiomyocyte developmental transcription factors (HAND1, HEY2, FOXM1, MEF2A, NR2F2, GATA6) are reported as “significantly downregulated in OCTN2-deficient cardiomyocytes,” consistent with impaired cardiomyocyte maintenance programs. (yin2024unravelingcardiomyocyteresponses pages 8-9, yin2024unravelingcardiomyocyteresponses pages 13-15)

• Signaling pathway shifts: Hippo and Wnt pathways are “found to be enriched”/altered; the authors report Hippo activation with decreased YAP1 and inhibition of canonical Wnt signaling. (yin2024unravelingcardiomyocyteresponses pages 8-9)

• Cell-type composition changes: five major cardiac cell types were identified (cardiomyocyte, fibroblast, neuron, macrophage, stem cell), with “significant aggregation of macrophage and fibroblast” and “significant reduction” in neurons in OCTN2-deficient hearts. (yin2024unravelingcardiomyocyteresponses pages 4-7)

Interpretation Together, these findings provide a plausible mechanistic bridge from an upstream metabolic transport defect (carnitine depletion and impaired β-oxidation) to myocardial remodeling: contractile dysfunction, immune activation, and fibroblast-driven ECM deposition/fibrosis, with altered trophic signaling and cellular composition. (yin2024unravelingcardiomyocyteresponses pages 1-2, yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15)

  1. Key molecular players (entities implicated in causality and progression)

3.1 Genes/proteins • SLC22A5 / OCTN2: canonical causative gene; OCTN2 is a Na+-dependent high-affinity carnitine transporter. A 2024 review notes the canonical OCTN2 is a 557-aa plasma membrane protein; an alternatively spliced OCTN2-VT is retained in the ER and is inactive for carnitine transport. (galluccio2024thehumanoctn pages 6-9)

• Variant-to-function impact: Galluccio et al. summarize a large functional survey of 150 OCTN2 missense variants (HEK293T 14C-carnitine uptake), reporting 71% with decreased transport and 37 variants with <20% WT activity, with many loss-of-function variants mapping to transmembrane domains and/or causing intracellular retention. (galluccio2024thehumanoctn pages 6-9)

• Secondary mediators implicated in cardiomyopathy remodeling (from snRNA-seq): GAS6, AXL, MERTK, SPP1, ITGAV/ITGB1; fibrosis-associated ECM genes (FN1, POSTN, COL1A2, ACTA2). (yin2024unravelingcardiomyocyteresponses pages 13-15, yin2024unravelingcardiomyocyteresponses pages 11-13)

3.2 Chemical entities/metabolites • L-carnitine (therapeutic replacement); free carnitine “C0” is the newborn screening biomarker. (zhou2024screeningprimarycarnitine pages 1-2, belaramani2024expandednewbornscreening pages 2-3) • Acylcarnitines (short/long chain): OCTN2 activity is inhibited by acylcarnitines and is involved in transport of carnitine conjugates; diagnostic follow-up commonly evaluates carnitine and acylcarnitines. (basan2024araretreatable pages 1-2, galluccio2024thehumanoctn pages 14-15) • Long-chain fatty acids (substrates whose mitochondrial utilization is impaired). (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2) • Ammonia (hyperammonemia reported in acute decompensation; implicated in encephalopathy). (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 5-7)

3.3 Cell types primarily affected • Cardiomyocytes: vulnerable due to reliance on fatty-acid oxidation; show contractile gene downregulation and altered signaling in OCTN2 deficiency. (yin2024unravelingcardiomyocyteresponses pages 1-2, yin2024unravelingcardiomyocyteresponses pages 8-9) • Cardiac fibroblasts: increased abundance and profibrotic activation (FN1/COL1A2/POSTN/ACTA2). (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15) • Macrophages (notably SPP1+ states): increased communication with cardiomyocytes and role in fibrosis signaling. (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15) • Neurons (cardiac-associated): decreased abundance and reduced VEGFA/VEGFR interaction signals reported in OCTN2-deficient hearts. (yin2024unravelingcardiomyocyteresponses pages 11-13) • Renal tubular epithelial cells (proximal tubule): central to carnitine reabsorption and therefore systemic carnitine homeostasis (mechanistic basis for renal carnitine leak). (kheirandish2024theroleof pages 4-5, basan2024araretreatable pages 1-2)

3.4 Anatomical locations (tissues/organs) OCTN2 is highlighted as highly expressed in myocardium, skeletal muscle, kidney (renal tubules), placenta, and intestine—consistent with systemic carnitine homeostasis and the major organ systems affected clinically. (yin2024unravelingcardiomyocyteresponses pages 1-2, zhou2024screeningprimarycarnitine pages 1-2)

  1. Biological processes (GO-style; disrupted processes) Representative disrupted processes supported by mechanistic evidence include: • Carnitine transmembrane transport / cellular carnitine uptake (defective due to OCTN2). (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 4-5) • Renal tubular reabsorption / carnitine homeostasis (renal leak in OCTN2 deficiency). (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 4-5) • Mitochondrial fatty-acid β-oxidation and oxidative energy metabolism (decreased due to impaired carnitine-dependent fatty-acid utilization). (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2) • Cardiac muscle contraction and calcium ion handling (downregulation of contractile and Ca2+ genes; RYR2 implicated). (yin2024unravelingcardiomyocyteresponses pages 8-9) • Extracellular matrix organization / collagen deposition / fibrosis and EMT-related remodeling (FN1, COL1A2, POSTN, ACTA2; EMT framing). (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15, yin2024unravelingcardiomyocyteresponses pages 8-9) • Immune cell activation and cytokine/ligand–receptor signaling shaping remodeling (SPP1, GAS6/AXL/MERTK intercellular axes). (yin2024unravelingcardiomyocyteresponses pages 13-15, yin2024unravelingcardiomyocyteresponses pages 11-13)

  2. Cellular components (where processes occur) • Plasma membrane: OCTN2 is a plasma membrane transporter; alternatively spliced OCTN2-VT is ER-retained and inactive. (galluccio2024thehumanoctn pages 6-9) • Endoplasmic reticulum: retention of OCTN2-VT indicates trafficking/localization as a mechanism of transport loss. (galluccio2024thehumanoctn pages 6-9) • Mitochondria: downstream metabolic dysfunction is centered on impaired mitochondrial β-oxidation. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2) • Extracellular space / extracellular matrix: fibrosis is reflected by ECM deposition and ECM-receptor interaction pathway changes. (yin2024unravelingcardiomyocyteresponses pages 4-7, yin2024unravelingcardiomyocyteresponses pages 8-9)

  3. Disease progression (sequence from trigger to clinical manifestation)

Initiation 1) Inherited biallelic pathogenic variants in SLC22A5 → reduced OCTN2 function via mislocalization/retention, pore disruption, or truncation, lowering cellular carnitine transport. (galluccio2024thehumanoctn pages 6-9, jolfayi2024anovelpathogenic pages 1-2)

Systemic biochemical stage 2) Reduced intestinal uptake and/or renal tubular reabsorption of carnitine → low plasma free carnitine and reduced tissue carnitine pools; urinary carnitine wasting is a central cause of systemic depletion. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2)

Metabolic stress stage 3) Mitochondrial long-chain fatty-acid β-oxidation impairment → reduced ATP generation during fasting/illness → metabolic decompensation (hypoketotic hypoglycemia, hyperammonemia, liver abnormalities, encephalopathy). (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 7-8)

Organ remodeling and cardiomyopathy stage 4) Chronic energy deficit and altered signaling in myocardium → depressed contractility gene programs, inflammation-linked signaling, fibroblast expansion, ECM deposition and fibrosis. snRNA-seq supports increased fibroblasts and macrophage-fibroblast/cardiomyocyte signaling (SPP1, GAS6), linking metabolic deficiency to structural remodeling. (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 13-15, yin2024unravelingcardiomyocyteresponses pages 4-7)

Clinical endpoints 5) Cardiomyopathy progression may include arrhythmias, heart failure, and sudden cardiac death; discontinuation or nonadherence to carnitine can precipitate poor outcomes (including reported sudden deaths when supplementation stopped, and arrhythmia progression with nonadherence). (yin2024unravelingcardiomyocyteresponses pages 1-2, basan2024araretreatable pages 2-4, stafford2024unmaskingprimarycarnitine pages 1-2)

  1. Phenotypic manifestations (HP-style; clinical features tied to mechanisms)

Metabolic crisis features (fasting/illness-driven) • Hypoketotic hypoglycemia and hyperammonemia (energy failure + altered nitrogen handling), with encephalopathy and abnormal liver tests in infants. (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 7-8)

Cardiac phenotypes • Dilated cardiomyopathy with reduced contractility, hypertrophic cardiomyopathy mimicry, arrhythmias, heart failure and possible sudden cardiac death; mechanistically supported by downregulation of cardiomyocyte contraction/Ca2+ genes and remodeling toward fibrosis. (yin2024unravelingcardiomyocyteresponses pages 1-2, yin2024unravelingcardiomyocyteresponses pages 8-9, stafford2024unmaskingprimarycarnitine pages 1-2)

Skeletal muscle phenotypes • Progressive muscle weakness/myopathy and hypotonia consistent with energy deficiency in oxidative tissues. (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 5-7)

Neurologic phenotypes • Encephalopathy in crises; emerging/translational evidence in the 2024 snRNA-seq study suggests altered neuron-associated signaling and reduced neurons in OCTN2-deficient hearts, potentially relevant to arrhythmia susceptibility. (yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 4-7)

  1. Recent developments (2023–2024) and latest research

8.1 Systems biology of PCD cardiomyopathy (2024) Yin et al. apply single-nucleus RNA-seq and ligand–receptor analyses to define cell-type remodeling and signaling axes in OCTN2-deficient cardiomyopathy, highlighting fibrosis initiation via GAS6/AXL and SPP1+ macrophage-driven fibroblast activation and ECM deposition, alongside suppression of cardiomyocyte contraction and calcium-handling genes. (yin2024unravelingcardiomyocyteresponses pages 13-15, yin2024unravelingcardiomyocyteresponses pages 11-13, yin2024unravelingcardiomyocyteresponses pages 8-9)

8.2 Transporter structure/function and regulation (2024) Recent OCTN2-focused transporter reviews emphasize: (i) isoforms including an ER-retained inactive splice variant, (ii) a broad landscape of functionally validated loss-of-function missense variants, and (iii) transcriptional regulation by nuclear receptors (e.g., PPARα/PPARγ) and other signaling pathways, supporting precision-medicine interpretation of variants and context-dependent carnitine homeostasis. (galluccio2024thehumanoctn pages 6-9, galluccio2024thehumanoctn pages 15-16)

8.3 Newborn screening: algorithmic refinement and genetic second-tier testing (2023–2024) • A 2023 worldwide overview emphasizes that NBS for PCD is “of high complexity” and highlights major pitfalls including “maternal carnitine deficiency… pivalic acid-based antibiotherapy, pre-term birth,” motivating multi-tier algorithms combining biochemical cutoffs, repeat DBS sampling, and molecular testing. (lefevre2023newbornscreeningof pages 1-2) • In 2024, second-tier NGS approaches demonstrated operational gains by reducing false positives and increasing PPV in NBS-positive infants (details in Section 9). (lin2024incorporatingnext‐generationsequencing pages 2-4, lin2024incorporatingnext‐generationsequencing pages 4-5)

  1. Current applications and real-world implementations

9.1 Newborn screening (NBS) Biomarker and key pitfalls NBS commonly uses tandem mass spectrometry to measure free carnitine (C0) in dried blood spots; however, placental/maternal carnitine transfer can cause false results, and programs may detect maternal PCD among infants flagged for low C0. (zhou2024screeningprimarycarnitine pages 1-2, ji2023primarycarnitinedeficiency pages 5-7, heuvel2023aqualitativestudy pages 1-2)

Algorithm design (example: France planning for expansion) A 2023 review describes a multi-step approach using C0 as first tier and additional retesting/second-tier molecular testing, and a third-tier day-21 repeat DBS to mitigate prematurity/maternal-related low C0 effects; it reports an aim to raise PPV “toward ~20%” via tiering strategies. (lefevre2023newbornscreeningof pages 7-8, lefevre2023newbornscreeningof pages 8-10)

Program performance statistics (Hong Kong) In a Hong Kong expanded NBS program (Oct 2015–Dec 2022), carnitine uptake defect (CUD/PCD) accounted for 9 true positives. The reported sensitivity was 100% with specificity 99.96% and PPV 16.6%, with 42 false positives. (belaramani2024expandednewbornscreening media fcd9c847)

9.2 Second-tier sequencing to improve NBS performance (2024) Lin et al. (Quanzhou, China) screened 60,070 newborns (2020) and applied targeted NGS to 130 infants with C0 < 8.5 μmol/L. Six infants had biallelic pathogenic SLC22A5 variants (incidence ~1/10,012). Adding second-tier NGS improved PPV from 4.62% (6/130) to 20% (6/30) by reducing recalls and classifying 76.92% (100/130) as genetically negative. (lin2024incorporatingnext‐generationsequencing pages 1-2, lin2024incorporatingnext‐generationsequencing pages 2-4)

9.3 Epidemiology and variant spectrum to guide implementation (2023–2024) • Meta-analysis across 9,958,380 Chinese newborns (476 cases) estimated prevalence 0.05‰ (≈1/20,000) with regional differences (southern 0.07‰ vs northern 0.02‰). Frequent variants included c.1400C>G (45%), c.51C>G (26%), and c.760C>T (14%). (zhou2024screeningprimarycarnitine pages 1-2, zhou2024screeningprimarycarnitine pages 5-8) • A 2023 China Neonatal Genomes Project analysis estimated prevalence ~1:17,456 (carrier frequency ~1:66), and reported genotype–phenotype associations: homozygous c.760C>T and c.844C>T were more likely to present cardiomyopathy, while homozygous c.1400C>G was more likely asymptomatic (p<0.05). It also reported conventional NBS missed 11.7% (2/17) of cases and proposed combining MS/MS with a high-frequency SLC22A5 variant panel for improved detection. (ji2023primarycarnitinedeficiency pages 1-2, ji2023primarycarnitinedeficiency pages 3-5, ji2023primarycarnitinedeficiency pages 5-7)

  1. Treatment: expert opinions and outcome data (recent clinical evidence)

L-carnitine replacement is the disease-modifying cornerstone PCD is repeatedly described as treatable and potentially reversible, especially for cardiomyopathy, with the key principle being early and continuous carnitine replacement. (basan2024araretreatable pages 1-2, lefevre2023newbornscreeningof pages 1-2)

Dose ranges and monitoring • Case-based implementation (2024): in an infant with dilated cardiomyopathy, L-carnitine 100 mg/kg/day increased free carnitine to 14 μmol/L by month 3 and normalized LV function by 6 months (LVEF 70%). (basan2024araretreatable pages 2-4) • Literature guidance cited in the same report recommends chronic oral 100–300 mg/kg/day. (basan2024araretreatable pages 2-4) • A 2024 review states lifelong high-dose oral L-carnitine is typical (100–200 mg/kg/day in three doses), with titration to plasma free carnitine and clinical response. (kheirandish2024theroleof pages 7-8)

Adherence and long-term outcomes • Clinical caution: “Two patients have died suddenly... when L-carnitine supplementation was discontinued,” supporting the view that sustained supplementation is critical. (basan2024araretreatable pages 2-4) • A 2024 cardiology case report documents nonadherence associated with arrhythmia/device rescues and progression of hypertrophy, whereas later compliance correlated with clinical stability. (stafford2024unmaskingprimarycarnitine pages 1-2)

Safety/implementation considerations High-dose L-carnitine is generally tolerated, but diarrhea and “fishy odor” (trimethylamine) may occur and be managed by dose adjustment or adjunctive measures. (kheirandish2024theroleof pages 7-8)

  1. Knowledge-base-ready annotations (ontology-oriented; examples)

11.1 Gene/protein annotations • Gene: SLC22A5 (protein: OCTN2), causal for PCD. (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2)

Suggested GO-style biological process annotations (evidence-based) • “carnitine transmembrane transport” (defective OCTN2-mediated uptake). (kheirandish2024theroleof pages 4-5) • “renal carnitine reabsorption / carnitine homeostasis” (renal leak). (basan2024araretreatable pages 1-2) • “fatty acid beta-oxidation” (impaired). (basan2024araretreatable pages 1-2, yin2024unravelingcardiomyocyteresponses pages 1-2) • “cardiac muscle contraction” and “calcium ion transport” (downregulated cardiomyocyte gene programs). (yin2024unravelingcardiomyocyteresponses pages 8-9) • “extracellular matrix organization” and “epithelial to mesenchymal transition” (fibrosis/EMT). (yin2024unravelingcardiomyocyteresponses pages 8-9, yin2024unravelingcardiomyocyteresponses pages 13-15)

Cellular component annotations • Plasma membrane (OCTN2 localization); endoplasmic reticulum (inactive ER-retained OCTN2-VT). (galluccio2024thehumanoctn pages 6-9) • Mitochondria (β-oxidation impairment). (basan2024araretreatable pages 1-2) • Extracellular matrix (fibrosis/ECM deposition). (yin2024unravelingcardiomyocyteresponses pages 11-13)

11.2 Phenotype associations (HP-style; examples) • Cardiomyopathy (dilated/hypertrophic), heart failure, arrhythmia/sudden death risk. (yin2024unravelingcardiomyocyteresponses pages 1-2, stafford2024unmaskingprimarycarnitine pages 1-2, basan2024araretreatable pages 2-4) • Hypoketotic hypoglycemia, hyperammonemia, encephalopathy. (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 7-8) • Myopathy/hypotonia/progressive muscle weakness. (basan2024araretreatable pages 1-2, kheirandish2024theroleof pages 5-7)

11.3 Cell type involvement (CL-style; examples) • Cardiomyocytes, fibroblasts, macrophages, neurons (cardiac-associated), renal tubular epithelial cells. (yin2024unravelingcardiomyocyteresponses pages 4-7, yin2024unravelingcardiomyocyteresponses pages 11-13, kheirandish2024theroleof pages 4-5)

11.4 Anatomical locations (UBERON-style; examples) • Heart/myocardium, skeletal muscle, kidney (renal tubules), liver, placenta, intestine. (yin2024unravelingcardiomyocyteresponses pages 1-2, kheirandish2024theroleof pages 4-5)

11.5 Chemical entities (ChEBI-style; examples) • L-carnitine; acylcarnitines; long-chain fatty acids; ammonia. (basan2024araretreatable pages 1-2, zhou2024screeningprimarycarnitine pages 1-2, kheirandish2024theroleof pages 5-7)

  1. Evidence items (PMID-linked where available in retrieved texts) The retrieved full-text excerpts used here did not consistently include PubMed identifiers in-line. The report therefore cites the primary sources by DOI/URL and provides mechanistic quotations directly from full text where available. Key genetic association evidence is consistent with curated databases and newborn-screening cohorts described in recent peer-reviewed sources. (galluccio2024thehumanoctn pages 6-9, zhou2024screeningprimarycarnitine pages 1-2, lin2024incorporatingnext‐generationsequencing pages 2-4)

Limitations of this synthesis • Some requested items (e.g., comprehensive, explicitly listed PMIDs for each mechanistic claim; transporter Km/Vmax kinetics) were not present in the available retrieved text snippets, so this report prioritizes DOI-linked primary/peer-reviewed sources and direct quoted statements from accessible full text. (galluccio2024thehumanoctn pages 6-9, yin2024unravelingcardiomyocyteresponses pages 13-15)

References

  1. (yin2024unravelingcardiomyocyteresponses pages 1-2): Yifan Yin, Liang Ye, Min Chen, Hao Liu, and Jing-kun Miao. Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus rna sequencing. Heliyon, 10:e33581, Jul 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e33581, doi:10.1016/j.heliyon.2024.e33581. This article has 2 citations.

  2. (zhou2024screeningprimarycarnitine pages 1-2): Jinfu Zhou, Guilin Li, Yinglin Zeng, Xiaolong Qiu, Peiran Zhao, Ting Huang, Xi Wang, Jinying Luo, Na Lin, and Liangpu Xu. Screening primary carnitine deficiency in 10 million chinese newborns: a systematic review and meta-analysis. Orphanet Journal of Rare Diseases, Jul 2024. URL: https://doi.org/10.1186/s13023-024-03267-x, doi:10.1186/s13023-024-03267-x. This article has 6 citations and is from a peer-reviewed journal.

  3. (galluccio2024thehumanoctn pages 6-9): Michele Galluccio, Martina Tripicchio, and Lorena Pochini. The human octn sub-family: gene and protein structure, expression, and regulation. International Journal of Molecular Sciences, 25:8743, Aug 2024. URL: https://doi.org/10.3390/ijms25168743, doi:10.3390/ijms25168743. This article has 5 citations.

  4. (pochini2024inflammationandorganic pages 3-5): Lorena Pochini, Michele Galluccio, Lara Console, Mariafrancesca Scalise, Ivano Eberini, and Cesare Indiveri. Inflammation and organic cation transporters novel (octns). Biomolecules, 14:392, Mar 2024. URL: https://doi.org/10.3390/biom14040392, doi:10.3390/biom14040392. This article has 14 citations.

  5. (lefevre2023newbornscreeningof pages 1-2): Charles R. Lefèvre, François Labarthe, Diane Dufour, Caroline Moreau, Marie Faoucher, Paul Rollier, Jean-Baptiste Arnoux, Marine Tardieu, Léna Damaj, Claude Bendavid, Anne-Frédérique Dessein, Cécile Acquaviva-Bourdain, and David Cheillan. Newborn screening of primary carnitine deficiency: an overview of worldwide practices and pitfalls to define an algorithm before expansion of newborn screening in france. International Journal of Neonatal Screening, 9:6, Feb 2023. URL: https://doi.org/10.3390/ijns9010006, doi:10.3390/ijns9010006. This article has 18 citations.

  6. (lin2024incorporatingnext‐generationsequencing pages 1-2): Yiming Lin, Zhenzhu Zheng, Weihua Lin, and Weilin Peng. Incorporating next‐generation sequencing as a second‐tier test for primary carnitine deficiency. Molecular Genetics & Genomic Medicine, Sep 2024. URL: https://doi.org/10.1002/mgg3.70003, doi:10.1002/mgg3.70003. This article has 3 citations and is from a peer-reviewed journal.

  7. (basan2024araretreatable pages 1-2): Hacer Basan, Emine Azak, İbrahim İlker Çetin, Esra Kılıç, Berrak Bilginer Gürbüz, Sümeyra Zeynep Özbey, and Çiğdem Seher Kasapkara. A rare treatable cause of cardiomyopathy: primary carnitine deficiency. Molecular Syndromology, 15:156-160, Nov 2024. URL: https://doi.org/10.1159/000534932, doi:10.1159/000534932. This article has 4 citations and is from a peer-reviewed journal.

  8. (jolfayi2024anovelpathogenic pages 1-2): Amir Ghaffari Jolfayi, Niloofar Naderi, Serwa Ghasemi, Alireza Salmanipour, Sara Adimi, Majid Maleki, and Samira Kalayinia. A novel pathogenic variant in the carnitine transporter gene, slc22a5, in association with metabolic carnitine deficiency and cardiomyopathy features. BMC Cardiovascular Disorders, Jan 2024. URL: https://doi.org/10.1186/s12872-023-03676-z, doi:10.1186/s12872-023-03676-z. This article has 5 citations and is from a peer-reviewed journal.

  9. (kheirandish2024theroleof pages 4-5): Ali Kheirandish, Reza Shah Hosseini, Shirin Yaghoobpoor, Ashkan Bahrami, Alireza Aghajani, M. Fathi, Milad Alipour, Ameneh Zarebidoki, and Ashraf Mohamadkhani. The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature. Gastroenterology and Hepatology From Bed to Bench, 17:357-378, 2024. URL: https://doi.org/10.22037/ghfbb.v17i4.2960, doi:10.22037/ghfbb.v17i4.2960. This article has 0 citations and is from a peer-reviewed journal.

  10. (kheirandish2024theroleof pages 7-8): Ali Kheirandish, Reza Shah Hosseini, Shirin Yaghoobpoor, Ashkan Bahrami, Alireza Aghajani, M. Fathi, Milad Alipour, Ameneh Zarebidoki, and Ashraf Mohamadkhani. The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature. Gastroenterology and Hepatology From Bed to Bench, 17:357-378, 2024. URL: https://doi.org/10.22037/ghfbb.v17i4.2960, doi:10.22037/ghfbb.v17i4.2960. This article has 0 citations and is from a peer-reviewed journal.

  11. (kheirandish2024theroleof pages 5-7): Ali Kheirandish, Reza Shah Hosseini, Shirin Yaghoobpoor, Ashkan Bahrami, Alireza Aghajani, M. Fathi, Milad Alipour, Ameneh Zarebidoki, and Ashraf Mohamadkhani. The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature. Gastroenterology and Hepatology From Bed to Bench, 17:357-378, 2024. URL: https://doi.org/10.22037/ghfbb.v17i4.2960, doi:10.22037/ghfbb.v17i4.2960. This article has 0 citations and is from a peer-reviewed journal.

  12. (yin2024unravelingcardiomyocyteresponses pages 8-9): Yifan Yin, Liang Ye, Min Chen, Hao Liu, and Jing-kun Miao. Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus rna sequencing. Heliyon, 10:e33581, Jul 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e33581, doi:10.1016/j.heliyon.2024.e33581. This article has 2 citations.

  13. (yin2024unravelingcardiomyocyteresponses pages 11-13): Yifan Yin, Liang Ye, Min Chen, Hao Liu, and Jing-kun Miao. Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus rna sequencing. Heliyon, 10:e33581, Jul 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e33581, doi:10.1016/j.heliyon.2024.e33581. This article has 2 citations.

  14. (yin2024unravelingcardiomyocyteresponses pages 13-15): Yifan Yin, Liang Ye, Min Chen, Hao Liu, and Jing-kun Miao. Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus rna sequencing. Heliyon, 10:e33581, Jul 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e33581, doi:10.1016/j.heliyon.2024.e33581. This article has 2 citations.

  15. (yin2024unravelingcardiomyocyteresponses pages 4-7): Yifan Yin, Liang Ye, Min Chen, Hao Liu, and Jing-kun Miao. Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus rna sequencing. Heliyon, 10:e33581, Jul 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e33581, doi:10.1016/j.heliyon.2024.e33581. This article has 2 citations.

  16. (belaramani2024expandednewbornscreening pages 2-3): Kiran Moti Belaramani, Toby Chun Hei Chan, Edgar Wai Lok Hau, Matthew Chun Wing Yeung, Anne Mei Kwun Kwok, Ivan Fai Man Lo, Terry Hiu Fung Law, Helen Wu, Sheila Suet Na Wong, Shirley Wai Lam, Gladys Ha Yin Ha, Toby Pui Yee Lau, Tsz Ki Wong, Venus Wai Ching Or, Rosanna Ming Sum Wong, Wong Lap Ming, Jasmine Chi Kwan Chow, Eric Kin Cheong Yau, Antony Fu, Josephine Shuk Ching Chong, Ho Chung Yau, Grace Wing Kit Poon, Kwok Leung Ng, Kwong Tat Chan, Yuen Yu Lam, Joannie Hui, Chloe Miu Mak, and Cheuk Wing Fung. Expanded newborn screening for inborn errors of metabolism in hong kong: results and outcome of a 7 year journey. International Journal of Neonatal Screening, 10:23, Mar 2024. URL: https://doi.org/10.3390/ijns10010023, doi:10.3390/ijns10010023. This article has 10 citations.

  17. (galluccio2024thehumanoctn pages 14-15): Michele Galluccio, Martina Tripicchio, and Lorena Pochini. The human octn sub-family: gene and protein structure, expression, and regulation. International Journal of Molecular Sciences, 25:8743, Aug 2024. URL: https://doi.org/10.3390/ijms25168743, doi:10.3390/ijms25168743. This article has 5 citations.

  18. (basan2024araretreatable pages 2-4): Hacer Basan, Emine Azak, İbrahim İlker Çetin, Esra Kılıç, Berrak Bilginer Gürbüz, Sümeyra Zeynep Özbey, and Çiğdem Seher Kasapkara. A rare treatable cause of cardiomyopathy: primary carnitine deficiency. Molecular Syndromology, 15:156-160, Nov 2024. URL: https://doi.org/10.1159/000534932, doi:10.1159/000534932. This article has 4 citations and is from a peer-reviewed journal.

  19. (stafford2024unmaskingprimarycarnitine pages 1-2): Sarah G. Stafford, Charlie J. Sang, Brian C. Jensen, Joseph A. Sivak, and Thelsa T. Weickert. Unmasking primary carnitine deficiency as a mimic of hypertrophic cardiomyopathy. JACC Case Reports, 29:102730, Nov 2024. URL: https://doi.org/10.1016/j.jaccas.2024.102730, doi:10.1016/j.jaccas.2024.102730. This article has 1 citations.

  20. (galluccio2024thehumanoctn pages 15-16): Michele Galluccio, Martina Tripicchio, and Lorena Pochini. The human octn sub-family: gene and protein structure, expression, and regulation. International Journal of Molecular Sciences, 25:8743, Aug 2024. URL: https://doi.org/10.3390/ijms25168743, doi:10.3390/ijms25168743. This article has 5 citations.

  21. (lin2024incorporatingnext‐generationsequencing pages 2-4): Yiming Lin, Zhenzhu Zheng, Weihua Lin, and Weilin Peng. Incorporating next‐generation sequencing as a second‐tier test for primary carnitine deficiency. Molecular Genetics & Genomic Medicine, Sep 2024. URL: https://doi.org/10.1002/mgg3.70003, doi:10.1002/mgg3.70003. This article has 3 citations and is from a peer-reviewed journal.

  22. (lin2024incorporatingnext‐generationsequencing pages 4-5): Yiming Lin, Zhenzhu Zheng, Weihua Lin, and Weilin Peng. Incorporating next‐generation sequencing as a second‐tier test for primary carnitine deficiency. Molecular Genetics & Genomic Medicine, Sep 2024. URL: https://doi.org/10.1002/mgg3.70003, doi:10.1002/mgg3.70003. This article has 3 citations and is from a peer-reviewed journal.

  23. (ji2023primarycarnitinedeficiency pages 5-7): Xiaoshan Ji, Yanzhuang Ge, Qi Ni, Suhua Xu, Zhongmeng Xiong, Lin Yang, Liyuan Hu, Yun Cao, Yulan Lu, Qiufen Wei, Wenqing Kang, Deyi Zhuang, Wenhao Zhou, and Xinran Dong. Primary carnitine deficiency: estimation of prevalence in chinese population and insights into newborn screening. Frontiers in Genetics, Dec 2023. URL: https://doi.org/10.3389/fgene.2023.1304458, doi:10.3389/fgene.2023.1304458. This article has 8 citations and is from a peer-reviewed journal.

  24. (heuvel2023aqualitativestudy pages 1-2): Lieke M. van den Heuvel, Adriana Kater-Kuipers, Tessa van Dijk, Loek L. Crefcoeur, Gepke Visser, Mirjam Langeveld, and Lidewij Henneman. A qualitative study on the perspectives of mothers who had been diagnosed with primary carnitine deficiency through newborn screening of their child. Orphanet Journal of Rare Diseases, Jun 2023. URL: https://doi.org/10.1186/s13023-023-02735-0, doi:10.1186/s13023-023-02735-0. This article has 5 citations and is from a peer-reviewed journal.

  25. (lefevre2023newbornscreeningof pages 7-8): Charles R. Lefèvre, François Labarthe, Diane Dufour, Caroline Moreau, Marie Faoucher, Paul Rollier, Jean-Baptiste Arnoux, Marine Tardieu, Léna Damaj, Claude Bendavid, Anne-Frédérique Dessein, Cécile Acquaviva-Bourdain, and David Cheillan. Newborn screening of primary carnitine deficiency: an overview of worldwide practices and pitfalls to define an algorithm before expansion of newborn screening in france. International Journal of Neonatal Screening, 9:6, Feb 2023. URL: https://doi.org/10.3390/ijns9010006, doi:10.3390/ijns9010006. This article has 18 citations.

  26. (lefevre2023newbornscreeningof pages 8-10): Charles R. Lefèvre, François Labarthe, Diane Dufour, Caroline Moreau, Marie Faoucher, Paul Rollier, Jean-Baptiste Arnoux, Marine Tardieu, Léna Damaj, Claude Bendavid, Anne-Frédérique Dessein, Cécile Acquaviva-Bourdain, and David Cheillan. Newborn screening of primary carnitine deficiency: an overview of worldwide practices and pitfalls to define an algorithm before expansion of newborn screening in france. International Journal of Neonatal Screening, 9:6, Feb 2023. URL: https://doi.org/10.3390/ijns9010006, doi:10.3390/ijns9010006. This article has 18 citations.

  27. (belaramani2024expandednewbornscreening media fcd9c847): Kiran Moti Belaramani, Toby Chun Hei Chan, Edgar Wai Lok Hau, Matthew Chun Wing Yeung, Anne Mei Kwun Kwok, Ivan Fai Man Lo, Terry Hiu Fung Law, Helen Wu, Sheila Suet Na Wong, Shirley Wai Lam, Gladys Ha Yin Ha, Toby Pui Yee Lau, Tsz Ki Wong, Venus Wai Ching Or, Rosanna Ming Sum Wong, Wong Lap Ming, Jasmine Chi Kwan Chow, Eric Kin Cheong Yau, Antony Fu, Josephine Shuk Ching Chong, Ho Chung Yau, Grace Wing Kit Poon, Kwok Leung Ng, Kwong Tat Chan, Yuen Yu Lam, Joannie Hui, Chloe Miu Mak, and Cheuk Wing Fung. Expanded newborn screening for inborn errors of metabolism in hong kong: results and outcome of a 7 year journey. International Journal of Neonatal Screening, 10:23, Mar 2024. URL: https://doi.org/10.3390/ijns10010023, doi:10.3390/ijns10010023. This article has 10 citations.

  28. (zhou2024screeningprimarycarnitine pages 5-8): Jinfu Zhou, Guilin Li, Yinglin Zeng, Xiaolong Qiu, Peiran Zhao, Ting Huang, Xi Wang, Jinying Luo, Na Lin, and Liangpu Xu. Screening primary carnitine deficiency in 10 million chinese newborns: a systematic review and meta-analysis. Orphanet Journal of Rare Diseases, Jul 2024. URL: https://doi.org/10.1186/s13023-024-03267-x, doi:10.1186/s13023-024-03267-x. This article has 6 citations and is from a peer-reviewed journal.

  29. (ji2023primarycarnitinedeficiency pages 1-2): Xiaoshan Ji, Yanzhuang Ge, Qi Ni, Suhua Xu, Zhongmeng Xiong, Lin Yang, Liyuan Hu, Yun Cao, Yulan Lu, Qiufen Wei, Wenqing Kang, Deyi Zhuang, Wenhao Zhou, and Xinran Dong. Primary carnitine deficiency: estimation of prevalence in chinese population and insights into newborn screening. Frontiers in Genetics, Dec 2023. URL: https://doi.org/10.3389/fgene.2023.1304458, doi:10.3389/fgene.2023.1304458. This article has 8 citations and is from a peer-reviewed journal.

  30. (ji2023primarycarnitinedeficiency pages 3-5): Xiaoshan Ji, Yanzhuang Ge, Qi Ni, Suhua Xu, Zhongmeng Xiong, Lin Yang, Liyuan Hu, Yun Cao, Yulan Lu, Qiufen Wei, Wenqing Kang, Deyi Zhuang, Wenhao Zhou, and Xinran Dong. Primary carnitine deficiency: estimation of prevalence in chinese population and insights into newborn screening. Frontiers in Genetics, Dec 2023. URL: https://doi.org/10.3389/fgene.2023.1304458, doi:10.3389/fgene.2023.1304458. This article has 8 citations and is from a peer-reviewed journal.