Primary carnitine deficiency (PCD) is an autosomal recessive disorder of fatty acid oxidation 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 renal tubular reabsorption of carnitine, causing systemic carnitine depletion and impaired mitochondrial long-chain fatty acid beta-oxidation. The clinical spectrum is bimodal, with acute metabolic decompensation in infancy (hypoketotic hypoglycemia, hyperammonemia, hepatic encephalopathy) and a more insidious cardiomyopathy phenotype (dilated or hypertrophic) often accompanied by skeletal myopathy. PCD is treatable with lifelong oral L-carnitine supplementation, which can reverse cardiomyopathy if started early. Estimated prevalence is approximately 1 in 20,000 in Chinese populations, with regional and ethnic variation.
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name: Primary Carnitine Deficiency
category: Mendelian
creation_date: '2025-06-12T20:16:27Z'
updated_date: '2026-05-20T06:19:54Z'
synonyms:
- Carnitine uptake defect
- CUD
- Carnitine transporter deficiency
- OCTN2 deficiency
- CDSP
- Systemic primary carnitine deficiency
description: 'Primary carnitine deficiency (PCD) is an autosomal recessive disorder of fatty acid oxidation 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 renal tubular reabsorption of carnitine, causing systemic carnitine depletion and impaired mitochondrial long-chain fatty acid beta-oxidation. The clinical spectrum is bimodal, with acute metabolic decompensation in infancy (hypoketotic hypoglycemia, hyperammonemia, hepatic encephalopathy) and a more insidious cardiomyopathy phenotype (dilated or hypertrophic) often accompanied by skeletal myopathy. PCD is treatable with lifelong oral L-carnitine supplementation, which can reverse cardiomyopathy if started early. Estimated prevalence is approximately 1 in 20,000 in Chinese populations, with regional and ethnic variation.
'
disease_term:
preferred_term: systemic primary carnitine deficiency disease
term:
id: MONDO:0008919
label: systemic primary carnitine deficiency disease
classifications:
harrisons_chapter:
- classification_value: hereditary disease
parents:
- Fatty Acid Oxidation Disorder
- Inborn Error of Metabolism
has_subtypes:
- name: Infantile acute metabolic primary carnitine deficiency
description: 'Early-onset subtype characterized by acute metabolic decompensation episodes with hypoketotic hypoglycemia, hyperammonemia, and encephalopathy, often precipitated by fasting or intercurrent illness.
'
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Supports an acute metabolic presentation subtype in PCD.
- name: Cardiac primary carnitine deficiency
description: 'Cardiac-dominant subtype with dilated or hypertrophic cardiomyopathy and heart failure risk, often with more insidious progression.
'
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Cardiomyopathy associated with PCD often presents with \nlife-threatening heart failure."
explanation: Supports a cardiac-predominant subtype with severe cardiomyopathy risk.
prevalence:
- notes: Meta-analysis of Chinese NBS data estimated prevalence of 1/20,000, with higher incidence in southern China (0.07 per mille) than northern China (0.02 per mille). China Neonatal Genomes Project estimated prevalence of approximately 1:17,456. Prevalence varies by ethnicity and region. In Hong Kong expanded NBS, carnitine uptake defect was the most common IMD identified (9 of 47 total IMD cases).
progression:
- notes: Disease progression proceeds from inherited biallelic SLC22A5 variants through systemic carnitine depletion, impaired fatty acid oxidation, and energy failure. In the acute metabolic form, fasting or illness precipitates hypoketotic hypoglycemia, hyperammonemia, and encephalopathy. In the cardiac form, chronic energy deficit leads to cardiomyocyte contractile dysfunction, fibrosis via GAS6/AXL and SPP1-driven macrophage-fibroblast signaling, and progressive cardiomyopathy with arrhythmia risk and possible sudden death. Discontinuation of carnitine supplementation can precipitate fatal outcomes.
pathophysiology:
- name: SLC22A5/OCTN2 transporter dysfunction
description: 'Loss-of-function variants in SLC22A5 impair OCTN2-mediated transmembrane carnitine transport in kidney and other tissues.
'
genes:
- preferred_term: SLC22A5
term:
id: hgnc:10969
label: SLC22A5
biological_processes:
- preferred_term: carnitine transmembrane transport
term:
id: GO:1902603
label: carnitine transmembrane transport
modifier: DECREASED
molecular_functions:
- preferred_term: transmembrane transporter activity
term:
id: GO:0022857
label: transmembrane transporter activity
modifier: DECREASED
cell_types:
- preferred_term: epithelial cell of proximal tubule
term:
id: CL:0002306
label: epithelial cell of proximal tubule
locations:
- preferred_term: kidney
term:
id: UBERON:0002113
label: kidney
evidence:
- reference: PMID:38961493
reference_title: "Screening primary carnitine deficiency in 10 million Chinese newborns: a systematic review and meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Primary carnitine deficiency (PCD) is a rare autosomal recessive \nfatty acid oxidation disorder caused by variants in SLC22A5, with its prevalence \nand SLC22A5 gene mutation spectrum varying across races and regions."
explanation: Confirms autosomal recessive etiology with SLC22A5 variants across populations.
downstream:
- target: Systemic carnitine depletion
description: Defective transport and renal reabsorption cause urinary carnitine wasting and low plasma/tissue carnitine.
- target: Urinary carnitine
description: Renal tubular OCTN2 dysfunction causes urinary carnitine wasting.
causal_link_type: DIRECT
- target: Free carnitine (C0)
description: Defective OCTN2-mediated carnitine transport and renal reabsorption produces low circulating free carnitine.
causal_link_type: DIRECT
- name: Systemic carnitine depletion
description: 'Defective renal tubular reabsorption causes urinary carnitine wasting, producing low plasma free carnitine and tissue carnitine depletion. This is the proximal biochemical consequence driving downstream metabolic failure.
'
biological_processes:
- preferred_term: carnitine transmembrane transport
term:
id: GO:1902603
label: carnitine transmembrane transport
modifier: DECREASED
cell_types:
- preferred_term: epithelial cell of proximal tubule
term:
id: CL:0002306
label: epithelial cell of proximal tubule
locations:
- preferred_term: kidney
term:
id: UBERON:0002113
label: kidney
chemical_entities:
- preferred_term: carnitine
term:
id: CHEBI:17126
label: carnitine
modifier: DECREASED
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: PARTIAL
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Supports systemic carnitine depletion as the proximal biochemical state linked to the clinical syndrome.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: As a result of its deficiency, carnitine is not reabsorbed in the kidney, leading to urinary loss and depletion of blood and tissue levels.
explanation: Review evidence directly supports OCTN2/CTD causing urinary carnitine loss and systemic carnitine depletion.
downstream:
- target: Impaired mitochondrial fatty acid beta-oxidation
description: Low intracellular carnitine limits mitochondrial import of long-chain fatty acids for beta-oxidation.
- target: Free carnitine (C0)
description: Systemic carnitine depletion is reflected by markedly reduced plasma free carnitine.
causal_link_type: DIRECT
evidence:
- reference: PMID:39248612
reference_title: "Incorporating Next-Generation Sequencing as a Second-Tier Test for Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Newborns with free carnitine (C0) levels below \n8.5 μmol/L were selected for second-tier genetic testing."
explanation: Newborn screening data support low C0 as the diagnostic biochemical readout of PCD.
- name: Impaired mitochondrial fatty acid beta-oxidation
description: 'Intracellular carnitine depletion impairs the carnitine shuttle system, reducing transfer of long-chain fatty acids into mitochondria for beta-oxidation. This causes energy failure particularly in tissues with high fatty acid oxidation demand such as heart and skeletal muscle, and drives metabolic decompensation during fasting or catabolic stress.
'
biological_processes:
- preferred_term: fatty acid beta-oxidation
term:
id: GO:0006635
label: fatty acid beta-oxidation
modifier: DECREASED
cell_types:
- preferred_term: cardiac muscle cell
term:
id: CL:0000746
label: cardiac muscle cell
- preferred_term: skeletal muscle fiber
term:
id: CL:0008002
label: skeletal muscle fiber
chemical_entities:
- preferred_term: carnitine
term:
id: CHEBI:17126
label: carnitine
modifier: DECREASED
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Confirms that carnitine depletion leads to both metabolic crises and cardiomyopathy.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Importantly, carnitine is necessary for import of long-chain fatty acyls-CoAs into mitochondria as acylcarnitines for FAO.
explanation: Supports impaired fatty-acid oxidation as the downstream consequence of carnitine depletion.
downstream:
- target: Cardiac remodeling and fibrosis in OCTN2 deficiency
- target: Hepatic metabolic decompensation
- target: Skeletal myopathy
description: Impaired fatty acid oxidation in skeletal muscle contributes to the myopathic presentation.
causal_link_type: DIRECT
- target: Muscular hypotonia
description: Energy deficiency in skeletal muscle contributes to hypotonia.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- target: Creatine kinase
description: Skeletal muscle energy failure and myopathy can increase creatine kinase.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Cardiac remodeling and fibrosis in OCTN2 deficiency
description: 'Chronic carnitine depletion in cardiomyocytes suppresses contractile and calcium-handling gene programs, triggers fibroblast expansion, and activates pro-fibrotic macrophage signaling. Single-nucleus RNA-seq studies of OCTN2-deficient hearts reveal downregulation of contractile genes (MYH7, TNNI3, TNNT2, RYR2), increased fibroblast abundance, elevated GAS6-AXL signaling initiating fibrosis through EMT, and SPP1-positive macrophage-driven fibroblast activation.
'
biological_processes:
- preferred_term: extracellular matrix organization
term:
id: GO:0030198
label: extracellular matrix organization
- preferred_term: cardiac muscle contraction
term:
id: GO:0060048
label: cardiac muscle contraction
cell_types:
- preferred_term: cardiac muscle cell
term:
id: CL:0000746
label: cardiac muscle cell
- preferred_term: fibroblast
term:
id: CL:0000057
label: fibroblast
- preferred_term: macrophage
term:
id: CL:0000235
label: macrophage
locations:
- preferred_term: heart
term:
id: UBERON:0000948
label: heart
evidence:
- reference: PMID:39091928
reference_title: "Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus RNA sequencing."
supports: SUPPORT
evidence_source: COMPUTATIONAL
snippet: "OCTN2-deficient cardiomyocytes displayed transcriptomic alterations \nindicative of reduced contractility, developmental abnormalities, and fibrosis."
explanation: Directly supports cardiac remodeling with reduced contractility and fibrosis in PCD.
downstream:
- target: Dilated cardiomyopathy
description: Cardiomyocyte contractile dysfunction and fibrosis produce the prevalent dilated cardiomyopathy phenotype.
causal_link_type: DIRECT
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Herein, we present a 10-month-old male patient with PCD, \nwhich was diagnosed while investigating the etiology of dilated cardiomyopathy \nand confirmed by molecular genetic analysis."
explanation: Supports dilated cardiomyopathy as a cardiac phenotype in molecularly confirmed PCD.
- target: Hypertrophic cardiomyopathy
description: PCD cardiomyopathy can also present as a hypertrophic cardiomyopathy phenocopy.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- target: Cardiac arrest
description: Severe cardiomyopathy and metabolic disturbance can culminate in sudden death or arrest.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- target: Ventricular arrhythmia
description: Cardiac energy failure and remodeling in CTD/PCD can produce life-threatening ventricular arrhythmias.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
evidence:
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Life-threatening arrhythmias can also occur, including nonsustained ventricular tachycardia with periods of sinus rhythm and ventricular premature beats, even in the presence of only borderline left ventricular hypertrophy.
explanation: Review evidence supports ventricular arrhythmias as a downstream cardiac manifestation of CTD/PCD.
- name: Hepatic metabolic decompensation
description: 'In the liver, carnitine deficiency impairs fatty acid oxidation and ketogenesis, leading to hypoketotic hypoglycemia during fasting. Accumulation of toxic metabolites contributes to hyperammonemia and hepatic encephalopathy, particularly in the infantile presentation of PCD.
'
biological_processes:
- preferred_term: ketone body biosynthetic process
term:
id: GO:0046951
label: ketone body biosynthetic process
modifier: DECREASED
cell_types:
- preferred_term: hepatocyte
term:
id: CL:0000182
label: hepatocyte
locations:
- preferred_term: liver
term:
id: UBERON:0002107
label: liver
chemical_entities:
- preferred_term: glucose
term:
id: CHEBI:17234
label: glucose
modifier: DECREASED
- preferred_term: ammonia
term:
id: CHEBI:16134
label: ammonia
modifier: INCREASED
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "Carnitine acts as a vital component in \nfacilitating the transport of long-chain fatty acids into the mitochondria, \nthereby enabling their oxidation for the generation of energy. Carnitine \nadditionally assumes a crucial role in the functionality of the brain. Carnitine \ndeficiency is associated with various types of inherited disorders related to \nlow levels of carnitine."
explanation: Supports carnitine's role in hepatic fatty acid oxidation and brain function, linking deficiency to encephalopathy.
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Confirms acute metabolic decompensation as a presentation of PCD.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Loss of carnitine in the kidney results in very low concentration in other tissues, resulting in severe impairment of long-chain FAO, which leads to hypoketotic hypoglycemia with fasting and stress.
explanation: Review evidence links carnitine loss to long-chain FAO impairment and hypoketotic hypoglycemia during fasting or stress.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: During episodes of metabolic decompensation, glucose and ketone bodies are inappropriately low. Transaminases and ammonia may be moderately elevated, and metabolic acidosis, prolonged prothrombin time, and elevated creatine kinase (CK) can occur.
explanation: Review evidence supports low glucose/ketones, hyperammonemia, and CK elevation during CTD decompensation.
downstream:
- target: Hypoketotic hypoglycemia
description: Impaired hepatic fatty acid oxidation and ketogenesis produces hypoketotic hypoglycemia during fasting.
causal_link_type: DIRECT
- target: Blood glucose
description: Acute metabolic decompensation includes decreased blood glucose during fasting stress.
causal_link_type: DIRECT
- target: Hyperammonemia
description: Acute hepatic metabolic disruption contributes to hyperammonemia.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- target: Ammonia
description: Hyperammonemia is the biochemical manifestation of increased ammonia during decompensation.
causal_link_type: DIRECT
- target: Encephalopathy
description: Hyperammonemia and hepatic energy failure contribute to metabolic encephalopathy.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- target: Lethargy
description: Acute encephalopathy can present with lethargy or decreased alertness.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
phenotypes:
- name: Dilated cardiomyopathy
frequency: FREQUENT
description: 'Dilated cardiomyopathy is the most common cardiac manifestation of PCD, presenting with reduced left ventricular ejection fraction and heart failure. It is often the presenting feature and can be reversed with L-carnitine supplementation.
'
phenotype_term:
preferred_term: Dilated cardiomyopathy
term:
id: HP:0001644
label: Dilated cardiomyopathy
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Cardiomyopathy associated with PCD often presents with \nlife-threatening heart failure."
explanation: Directly supports cardiomyopathy as a frequent life-threatening manifestation.
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Herein, we present a 10-month-old male patient with PCD, \nwhich was diagnosed while investigating the etiology of dilated cardiomyopathy \nand confirmed by molecular genetic analysis."
explanation: Confirms dilated cardiomyopathy as the presenting feature in a molecularly confirmed PCD case.
- name: Hypertrophic cardiomyopathy
frequency: OCCASIONAL
description: 'PCD can mimic hypertrophic cardiomyopathy and may be mistakenly attributed to sarcomeric protein dysfunction. Recognition of this phenocopy is important for appropriate management.
'
phenotype_term:
preferred_term: Hypertrophic cardiomyopathy
term:
id: HP:0001639
label: Hypertrophic cardiomyopathy
evidence:
- reference: PMID:39691889
reference_title: "Unmasking Primary Carnitine Deficiency as a Mimic of Hypertrophic Cardiomyopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Primary carnitine deficiency may mimic hypertrophic cardiomyopathy and be \nmistakenly attributed to genotype-negative sarcomeric protein dysfunction in \nhypertrophic cardiomyopathy."
explanation: Directly supports HCM as a phenocopy presentation of PCD.
- reference: PMID:38166572
reference_title: "A novel pathogenic variant in the carnitine transporter gene, SLC22A5, in association with metabolic carnitine deficiency and cardiomyopathy features."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Clinical evaluations, echocardiography, and cardiac magnetic resonance \nimaging findings revealed hypertrophic cardiomyopathy as a clinical presentation \nof PCD."
explanation: Confirms HCM as a clinical presentation in a confirmed PCD case.
- name: Hypoketotic hypoglycemia
frequency: FREQUENT
description: 'Fasting intolerance with impaired ketogenesis and hypoglycemia is a hallmark of acute metabolic decompensation in PCD, especially in infants during intercurrent illness.
'
phenotype_term:
preferred_term: Hypoketotic hypoglycemia
term:
id: HP:0001985
label: Hypoketotic hypoglycemia
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Supports metabolic decompensation as a clinical presentation, which includes hypoketotic hypoglycemia.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Loss of carnitine in the kidney results in very low concentration in other tissues, resulting in severe impairment of long-chain FAO, which leads to hypoketotic hypoglycemia with fasting and stress.
explanation: Directly supports hypoketotic hypoglycemia as a downstream consequence of CTD under fasting or stress.
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "Carnitine \ndeficiency is associated with various types of inherited disorders related to \nlow levels of carnitine."
explanation: Supports carnitine deficiency as the underlying cause of metabolic decompensation features.
- name: Hyperammonemia
frequency: OCCASIONAL
description: 'Secondary hyperammonemia occurs during acute metabolic decompensation, contributing to encephalopathy. The mechanism involves impaired urea cycle function secondary to metabolic disruption.
'
phenotype_term:
preferred_term: Hyperammonemia
term:
id: HP:0001987
label: Hyperammonemia
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "A strong correlation exists between the insufficiency \nof carnitine and the occurrence of HE."
explanation: Supports the link between carnitine deficiency and hyperammonemia/encephalopathy.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: During episodes of metabolic decompensation, glucose and ketone bodies are inappropriately low. Transaminases and ammonia may be moderately elevated, and metabolic acidosis, prolonged prothrombin time, and elevated creatine kinase (CK) can occur.
explanation: Directly supports ammonia elevation during CTD metabolic decompensation.
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Metabolic decompensation in PCD includes hyperammonemia.
- name: Skeletal myopathy
frequency: FREQUENT
description: 'Progressive skeletal muscle weakness and hypotonia result from energy deficiency in oxidative muscle fibers. Myopathy may accompany the cardiomyopathy phenotype.
'
phenotype_term:
preferred_term: Myopathy
term:
id: HP:0003198
label: Myopathy
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This presentation also usually includes skeletal \nmuscle myopathy."
explanation: Directly supports skeletal myopathy as a frequent accompanying feature.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Later-onset disorders can present with milder skeletal muscle manifestations, including hypotonia, myopathy, and exercise intolerance.
explanation: Review evidence supports skeletal muscle involvement in CTD.
- name: Muscular hypotonia
frequency: FREQUENT
description: 'Hypotonia is a common neuromuscular finding in PCD, related to impaired energy metabolism in skeletal muscle.
'
phenotype_term:
preferred_term: Hypotonia
term:
id: HP:0001252
label: Hypotonia
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This presentation also usually includes skeletal \nmuscle myopathy."
explanation: Skeletal myopathy presentation is consistent with hypotonia as a feature.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Later-onset disorders can present with milder skeletal muscle manifestations, including hypotonia, myopathy, and exercise intolerance.
explanation: Directly supports hypotonia as a skeletal muscle manifestation of CTD.
- name: Lethargy
frequency: OCCASIONAL
description: 'Decreased alertness and lethargy occur during acute metabolic decompensation and may progress to encephalopathy.
'
phenotype_term:
preferred_term: Lethargy
term:
id: HP:0001254
label: Lethargy
evidence:
- reference: PMID:38166572
reference_title: "A novel pathogenic variant in the carnitine transporter gene, SLC22A5, in association with metabolic carnitine deficiency and cardiomyopathy features."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We herein describe an 8-year-old boy with symptoms of weakness and \nlethargy diagnosed with PCD through clinical evaluations, lab tests, \nechocardiography, and cardiac magnetic resonance imaging."
explanation: Directly reports lethargy as a presenting symptom in a confirmed PCD patient. Frequency based on limited case reports.
- name: Cardiac arrest
frequency: VERY_RARE
description: 'Sudden cardiac death or arrest can occur in untreated PCD or with discontinuation of L-carnitine supplementation. Arrhythmias secondary to cardiomyopathy contribute to this risk.
'
phenotype_term:
preferred_term: Cardiac arrest
term:
id: HP:0001695
label: Cardiac arrest
evidence:
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Life-threatening arrhythmias can also occur, including nonsustained ventricular tachycardia with periods of sinus rhythm and ventricular premature beats, even in the presence of only borderline left ventricular hypertrophy.
explanation: Review evidence supports life-threatening arrhythmia risk in CTD/PCD, consistent with sudden cardiac death or arrest risk.
- name: Ventricular arrhythmia
frequency: OCCASIONAL
description: 'Life-threatening ventricular arrhythmias, including nonsustained ventricular tachycardia and ventricular premature beats, can occur in CTD/PCD and may contribute to sudden cardiac death risk.
'
phenotype_term:
preferred_term: Ventricular arrhythmia
term:
id: HP:0004308
label: Ventricular arrhythmia
evidence:
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: Life-threatening arrhythmias can also occur, including nonsustained ventricular tachycardia with periods of sinus rhythm and ventricular premature beats, even in the presence of only borderline left ventricular hypertrophy.
explanation: Directly supports ventricular arrhythmias as a cardiac manifestation of CTD/PCD.
sequelae:
- target: Cardiac arrest
description: Life-threatening ventricular arrhythmias can progress to sudden cardiac arrest or death.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Encephalopathy
frequency: OCCASIONAL
description: 'Metabolic encephalopathy occurs during acute decompensation episodes, presenting with altered consciousness ranging from excessive sleepiness to coma.
'
phenotype_term:
preferred_term: Encephalopathy
term:
id: HP:0001298
label: Encephalopathy
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "A strong correlation exists between the insufficiency \nof carnitine and the occurrence of HE."
explanation: Supports encephalopathy risk in severe carnitine deficiency through association with hepatic encephalopathy.
biochemical:
- name: Free carnitine (C0)
presence: DECREASED
context: 'Markedly reduced plasma free carnitine (C0) is the primary diagnostic biomarker for PCD. It is the first-tier newborn screening analyte measured by tandem mass spectrometry in dried blood spots. In one newborn-screening cohort, infants with C0 levels below 8.5 μmol/L were selected for second-tier genetic testing.
'
biomarker_term:
preferred_term: carnitine
term:
id: CHEBI:17126
label: carnitine
readouts:
- target: SLC22A5/OCTN2 transporter dysfunction
relationship: READOUT_OF
direction: NEGATIVE
endpoint_context: DIAGNOSTIC
interpretation: >
Low plasma free carnitine reports failed OCTN2-mediated carnitine uptake
and renal reabsorption.
- target: Systemic carnitine depletion
relationship: READOUT_OF
direction: NEGATIVE
endpoint_context: DIAGNOSTIC
interpretation: >
Free carnitine (C0) is the primary circulating readout of systemic
carnitine depletion in PCD.
evidence:
- reference: PMID:39248612
reference_title: "Incorporating Next-Generation Sequencing as a Second-Tier Test for Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Newborns with free carnitine (C0) levels below \n8.5 μmol/L were selected for second-tier genetic testing."
explanation: Directly supports low C0 as the NBS trigger biomarker threshold in PCD screening workflows.
- name: Urinary carnitine
presence: INCREASED
context: 'Elevated urinary carnitine excretion (carnitine wasting) results from defective OCTN2-mediated renal tubular reabsorption and is a hallmark of PCD. Fractional excretion of carnitine is markedly increased.
'
biomarker_term:
preferred_term: carnitine
term:
id: CHEBI:17126
label: carnitine
readouts:
- target: SLC22A5/OCTN2 transporter dysfunction
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: DIAGNOSTIC
interpretation: >
Increased urinary carnitine excretion reports defective proximal-tubule
OCTN2 reabsorption.
- target: Systemic carnitine depletion
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: MONITORING
interpretation: >
Urinary carnitine wasting explains and tracks the systemic carnitine
depletion state.
evidence:
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: CTD deficiency should be suspected by the finding of very low free plasma carnitine concentrations (<10 μmol/L) accompanied by increased fractional excretion of carnitine in urine.
explanation: Directly supports increased fractional urinary carnitine excretion in CTD/PCD.
- name: Ammonia
presence: INCREASED
context: 'Hyperammonemia occurs during acute metabolic decompensation episodes and contributes to encephalopathy. Elevated ammonia results from secondary impairment of urea cycle function.
'
biomarker_term:
preferred_term: ammonia
term:
id: CHEBI:16134
label: ammonia
readouts:
- target: Hepatic metabolic decompensation
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: MONITORING
interpretation: >
Elevated ammonia reports acute hepatic metabolic decompensation during
fasting or stress.
- target: Hyperammonemia
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: DIAGNOSTIC
interpretation: >
Blood ammonia is the direct biochemical readout of the hyperammonemia
phenotype.
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "A strong correlation exists between the insufficiency \nof carnitine and the occurrence of HE."
explanation: Links carnitine deficiency to hyperammonemia and hepatic encephalopathy.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: During episodes of metabolic decompensation, glucose and ketone bodies are inappropriately low. Transaminases and ammonia may be moderately elevated, and metabolic acidosis, prolonged prothrombin time, and elevated creatine kinase (CK) can occur.
explanation: Directly supports ammonia elevation during CTD metabolic decompensation.
- name: Blood glucose
presence: DECREASED
context: 'Hypoketotic hypoglycemia occurs during fasting or metabolic stress due to impaired fatty acid oxidation and inadequate alternative energy substrate generation.
'
biomarker_term:
preferred_term: glucose
term:
id: CHEBI:17234
label: glucose
readouts:
- target: Hepatic metabolic decompensation
relationship: READOUT_OF
direction: NEGATIVE
endpoint_context: MONITORING
interpretation: >
Low blood glucose reports failure of hepatic energy production during
decompensation.
- target: Hypoketotic hypoglycemia
relationship: READOUT_OF
direction: NEGATIVE
endpoint_context: DIAGNOSTIC
interpretation: Blood glucose is the direct biochemical readout of hypoglycemia.
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Acute metabolic decompensation in PCD includes hypoglycemia.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: During episodes of metabolic decompensation, glucose and ketone bodies are inappropriately low.
explanation: Directly supports low glucose during CTD metabolic decompensation.
- name: Creatine kinase
presence: INCREASED
context: 'Elevated creatine kinase may be seen in patients with skeletal myopathy or during acute episodes, reflecting muscle damage from energy failure.
'
biomarker_term:
preferred_term: Creatine Kinase
term:
id: NCIT:C113245
label: Creatine Kinase
readouts:
- target: Skeletal myopathy
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: MONITORING
interpretation: >
Elevated creatine kinase tracks muscle injury in the myopathic
presentation.
- target: Impaired mitochondrial fatty acid beta-oxidation
relationship: READOUT_OF
direction: POSITIVE
endpoint_context: MONITORING
interpretation: >
Creatine kinase elevation is a downstream laboratory readout of muscle
energy failure during PCD decompensation.
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This presentation also usually includes skeletal \nmuscle myopathy."
explanation: Skeletal myopathy in PCD is consistent with CK elevation.
- reference: PMID:29502916
reference_title: "Inborn Errors of Metabolism with Myopathy: Defects of Fatty Acid Oxidation and the Carnitine Shuttle System."
supports: SUPPORT
evidence_source: OTHER
snippet: During episodes of metabolic decompensation, glucose and ketone bodies are inappropriately low. Transaminases and ammonia may be moderately elevated, and metabolic acidosis, prolonged prothrombin time, and elevated creatine kinase (CK) can occur.
explanation: Directly supports CK elevation during CTD metabolic decompensation.
genetic:
- name: SLC22A5 (OCTN2) pathogenic variants
gene_term:
preferred_term: SLC22A5
term:
id: hgnc:10969
label: SLC22A5
inheritance:
- name: Autosomal recessive
evidence:
- reference: PMID:38961493
reference_title: "Screening primary carnitine deficiency in 10 million Chinese newborns: a systematic review and meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Primary carnitine deficiency (PCD) is a rare autosomal recessive \nfatty acid oxidation disorder caused by variants in SLC22A5"
explanation: Directly confirms autosomal recessive inheritance.
variants:
- name: SLC22A5 - c.1400C>G (p.Ser467Cys)
description: 'The most common pathogenic variant in Chinese PCD patients, accounting for approximately 45% of alleles. Regional variation exists with lower frequency in southern China.
'
- name: SLC22A5 - c.51C>G (p.Phe17Leu)
description: 'Second most common variant in Chinese PCD, accounting for approximately 26% of alleles.
'
- name: SLC22A5 - c.760C>T (p.Arg254*)
description: 'Nonsense variant accounting for approximately 14% of alleles in Chinese PCD. Homozygous c.760C>T carriers are more likely to present with cardiomyopathy.
'
evidence:
- reference: PMID:38125748
reference_title: "Primary carnitine deficiency: Estimation of prevalence in Chinese population and insights into newborn screening."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "patients \ncarrying homozygous c.760C>T and c.844C>T were more likely to present \ncardiomyopathy, whereas those carrying homozygous c.1400C>G were more likely to \nbe asymptomatic"
explanation: Establishes genotype-phenotype correlation for c.760C>T with cardiomyopathy.
- reference: PMID:39248612
reference_title: "Incorporating Next-Generation Sequencing as a Second-Tier Test for Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the three most common variants were \nc.760C>T (p.Arg254*), c.51C>G (p.Phe17Leu), and c.1400C>G (p.Ser467Cys)."
explanation: Confirms c.760C>T as a common PCD variant.
- name: SLC22A5 - c.821G>A (p.Trp274Ter)
description: 'Novel nonsense variant identified in an Iranian family, associated with hypertrophic cardiomyopathy. Docking analysis demonstrated reduced carnitine binding affinity.
'
evidence:
- reference: PMID:38166572
reference_title: "A novel pathogenic variant in the carnitine transporter gene, SLC22A5, in association with metabolic carnitine deficiency and cardiomyopathy features."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Whole-exome sequencing identified a new homozygous variant, SLC22A5 \n(NM_003060.4), c.821G > A: p.Trp274Ter, associated with carnitine transport."
explanation: Reports the novel pathogenic variant with functional impact on OCTN2.
features: 'Biallelic pathogenic variants in SLC22A5 abolish or severely reduce OCTN2-mediated carnitine transport. Common variants in Chinese cohorts include c.1400C>G, c.51C>G, and c.760C>T, with regional variation. Genotype-phenotype correlations exist, with homozygous c.760C>T and c.844C>T more likely to cause cardiomyopathy, while homozygous c.1400C>G tends toward asymptomatic presentation. Broader OCTN reviews note many additional missense variants of uncertain clinical significance.
'
evidence:
- reference: PMID:39201429
reference_title: "The Human OCTN Sub-Family: Gene and Protein Structure, Expression, and Regulation."
supports: SUPPORT
evidence_source: OTHER
snippet: "A \nplethora of missense variants with uncertain clinical significance are reported \nboth in the dbSNP and the Catalogue of Somatic Mutations in Cancer (COSMIC) \ndatabases for both genes."
explanation: Supports that many OCTN-family missense variants are reported, while their clinical significance is often uncertain.
- reference: CGGV:assertion_2beee8a9-193c-41ca-92c4-484c8e034b02-2018-04-24T160000.000Z
reference_title: "SLC22A5 / systemic primary carnitine deficiency disease (Definitive)"
supports: SUPPORT
evidence_source: OTHER
snippet: "SLC22A5 | HGNC:10969 | systemic primary carnitine deficiency disease | MONDO:0008919 | AR | Definitive"
explanation: ClinGen classifies the SLC22A5-systemic primary carnitine deficiency disease gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: L-carnitine supplementation
description: 'Lifelong oral L-carnitine replacement is the disease-modifying cornerstone of PCD management. Standard dosing is 100-300 mg/kg/day in divided doses, titrated to plasma free carnitine levels and clinical response. Early treatment can reverse cardiomyopathy, with LVEF normalization reported within months.
'
treatment_term:
preferred_term: carnitine supplementation
term:
id: MAXO:0010006
label: carnitine supplementation
target_phenotypes:
- preferred_term: Dilated cardiomyopathy
term:
id: HP:0001644
label: Dilated cardiomyopathy
target_mechanisms:
- target: Systemic carnitine depletion
treatment_effect: RESTORES
description: Oral L-carnitine directly restores low free carnitine levels and improves symptoms and cardiac function.
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "With oral L-carnitine supplementation, the free \ncarnitine level increased up to 14 μmol/L and the symptoms disappeared. LVEF \nincreased by 45-70%."
explanation: Demonstrates biochemical restoration and cardiac improvement after oral L-carnitine in a confirmed PCD case.
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Early recognition of this disorder and treatment with carnitine \ncan avoid life-threatening complications related to cardiomyopathy."
explanation: Supports the critical importance of early carnitine treatment.
- name: Dietary management
description: 'Avoidance of prolonged fasting is essential to prevent metabolic decompensation. Frequent feeding schedules and carbohydrate-rich snacks before bed help maintain energy supply and reduce dependence on fatty acid oxidation.
'
treatment_term:
preferred_term: dietary intervention
term:
id: MAXO:0000088
label: dietary intervention
target_phenotypes:
- preferred_term: Hypoketotic hypoglycemia
term:
id: HP:0001985
label: Hypoketotic hypoglycemia
target_mechanisms:
- target: Impaired mitochondrial fatty acid beta-oxidation
treatment_effect: BYPASSES
description: Frequent carbohydrate intake and fasting avoidance reduce dependence on impaired fatty-acid oxidation during catabolic stress.
evidence:
- reference: PMID:39203843
reference_title: "Nutritional Management of Patients with Fatty Acid Oxidation Disorders."
supports: SUPPORT
evidence_source: OTHER
snippet: "Dietary management consists of preventing periods of \nfasting and restricting fat intake by increasing carbohydrate intake, while \nmaintaining an adequate and uninterrupted caloric intake."
explanation: General FAOD nutritional guidance supports carbohydrate-based fasting avoidance as bypass management for impaired fatty-acid oxidation.
evidence:
- reference: PMID:39203843
reference_title: "Nutritional Management of Patients with Fatty Acid Oxidation Disorders."
supports: SUPPORT
evidence_source: OTHER
snippet: "Treatment of fatty acid oxidation disorders is based on dietary, pharmacological \nand metabolic decompensation measures."
explanation: Supports dietary management as part of standard FAOD care.
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Prevention of metabolic decompensation through dietary management is a standard approach.
- name: Acute decompensation management
description: 'Emergency supportive care during metabolic crises includes intravenous glucose infusion to reverse catabolism, correction of metabolic acidosis, treatment of hyperammonemia, and intravenous L-carnitine. Prompt intervention prevents progression to encephalopathy and organ failure.
'
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
target_phenotypes:
- preferred_term: Hypoketotic hypoglycemia
term:
id: HP:0001985
label: Hypoketotic hypoglycemia
- preferred_term: Encephalopathy
term:
id: HP:0001298
label: Encephalopathy
target_mechanisms:
- target: Hepatic metabolic decompensation
treatment_effect: BYPASSES
description: Intravenous glucose reverses catabolism and bypasses reliance on impaired fatty-acid oxidation during acute metabolic crises.
evidence:
- reference: PMID:39203843
reference_title: "Nutritional Management of Patients with Fatty Acid Oxidation Disorders."
supports: SUPPORT
evidence_source: OTHER
snippet: "The main measure in emergency hospital treatment is the \nadministration of IV glucose."
explanation: Supports IV glucose as emergency metabolic decompensation management in FAODs.
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Carnitine deficiency can result in \nacute metabolic decompensation or, in a more insidious presentation, \ncardiomyopathy."
explanation: Acute metabolic decompensation requires emergency supportive management.
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "If a deficiency of carnitine is \nidentified through clinical symptoms or laboratory results in patients with \nliver dysfunction, treatment with carnitine replacement therapy is recommended."
explanation: Supports carnitine replacement as treatment during acute episodes.
- name: Newborn screening
description: 'NBS for PCD uses tandem mass spectrometry to measure free carnitine (C0) in dried blood spots. The condition is of high screening complexity due to pitfalls including maternal PCD, premature birth, and medication effects on C0 levels. Second-tier NGS testing can improve positive predictive value from approximately 5% to 20%.
'
treatment_term:
preferred_term: disease screening
term:
id: MAXO:0000124
label: disease screening
evidence:
- reference: PMID:36810318
reference_title: "Newborn Screening of Primary Carnitine Deficiency: An Overview of Worldwide Practices and Pitfalls to Define an Algorithm before Expansion of Newborn Screening in France."
supports: SUPPORT
evidence_source: OTHER
snippet: "This disease is of high complexity to screen, due to its \npathophysiology and wide clinical spectrum."
explanation: Confirms the complexity and importance of NBS for PCD.
- reference: PMID:39248612
reference_title: "Incorporating Next-Generation Sequencing as a Second-Tier Test for Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The PPV reached 20% after combining with second-tier NGS.
explanation: Demonstrates improved screening performance with NGS second-tier testing.
- name: Cardiac management
description: 'Standard heart failure therapy including ACE inhibitors, beta-blockers, and diuretics may be required for patients presenting with cardiomyopathy and heart failure. Cardiac monitoring with echocardiography is essential for long-term follow-up. ICD placement may be considered for arrhythmia management.
'
treatment_term:
preferred_term: pharmacotherapy
term:
id: MAXO:0000058
label: pharmacotherapy
target_phenotypes:
- preferred_term: Dilated cardiomyopathy
term:
id: HP:0001644
label: Dilated cardiomyopathy
- preferred_term: Hypertrophic cardiomyopathy
term:
id: HP:0001639
label: Hypertrophic cardiomyopathy
evidence:
- reference: PMID:38585546
reference_title: "A Rare Treatable Cause of Cardiomyopathy: Primary Carnitine Deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Cardiomyopathy associated with PCD often presents with \nlife-threatening heart failure."
explanation: Heart failure presentation necessitates cardiac pharmacotherapy.
- name: Genetic counseling
description: 'Genetic counseling is essential for affected families, including discussion of autosomal recessive inheritance, 25% recurrence risk for each pregnancy, carrier testing for family members, and prenatal or preimplantation genetic testing options. NBS may also detect maternal PCD through low C0 in the infant.
'
treatment_term:
preferred_term: genetic counseling
term:
id: MAXO:0000079
label: genetic counseling
evidence:
- reference: PMID:38961493
reference_title: "Screening primary carnitine deficiency in 10 million Chinese newborns: a systematic review and meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Primary carnitine deficiency (PCD) is a rare autosomal recessive \nfatty acid oxidation disorder caused by variants in SLC22A5"
explanation: Autosomal recessive etiology mandates genetic counseling for affected families.
- name: Acetyl-L-carnitine for encephalopathy
description: 'Administration of acetyl-L-carnitine in patients with hepatic encephalopathy associated with carnitine deficiency can improve mental and psychological conditions, representing an adjunctive therapeutic approach.
'
treatment_term:
preferred_term: carnitine supplementation
term:
id: MAXO:0010006
label: carnitine supplementation
target_phenotypes:
- preferred_term: Encephalopathy
term:
id: HP:0001298
label: Encephalopathy
target_mechanisms:
- target: Hepatic metabolic decompensation
treatment_effect: MODULATES
description: Acetyl-L-carnitine is described as improving mental and psychological manifestations in carnitine-associated hepatic encephalopathy.
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "Thus, the administration of acetyl-L-carnitine in patients with HE can improve \ntheir mental and psychological conditions."
explanation: Review evidence supports acetyl-L-carnitine as an adjunct for hepatic encephalopathy related to carnitine deficiency.
evidence:
- reference: PMID:40406429
reference_title: "The role of genetic defects in carnitine-associated hepatic encephalopathy: a review of literature."
supports: SUPPORT
evidence_source: OTHER
snippet: "the administration of acetyl-L-carnitine in patients with HE can improve \ntheir mental and psychological conditions."
explanation: Directly supports acetyl-L-carnitine as treatment for carnitine-associated encephalopathy.
notes: 'PCD is considered one of the most treatable inborn errors of metabolism, with cardiomyopathy often fully reversible if diagnosed and treated early. However, discontinuation of L-carnitine supplementation can be fatal, with reports of sudden death when supplementation was stopped. NBS programs are expanding worldwide but face challenges with false positives due to maternal PCD, premature birth, and medication effects. Side effects of high-dose carnitine include diarrhea and fishy body odor (trimethylamine). The 2024 single-nucleus RNA-seq study of OCTN2-deficient hearts provides new mechanistic insights into cardiomyopathy progression through fibrosis pathways.
'
references: []
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.
Please provide a comprehensive research report on the pathophysiology of Primary Carnitine Deficiency. Focus on the molecular and cellular mechanisms underlying disease progression.
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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)
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
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