Primary carnitine deficiency cardiomyopathy

Unraveling cardiomyocyte responses and intercellular communication alterations in primary carnitine deficiency cardiomyopathy via single-nucleus RNA sequencing

Background

Primary Carnitine Deficiency (PCD) is a potentially life-threatening autosomal recessive monogenic disorder arising from mutations in the organic cation transporter 2 (OCTN2) gene. Dilated cardiomyopathy (DCM) is a prevalent symptom associated with this condition, and episodes of metabolic disturbance may lead to sudden death. However, the pathogenic mechanism remains unclear. Here, we sought to investigate the response of cardiomyocytes and alterations in the intercellular communication in individuals with PCD DCM.

Methods

The GSE211650 dataset was downloaded. Subsequently, modular analysis was performed using hdWGCNA. SCENIC was employed for transcription factor analysis. Monocle2 and SCP were applied to conduct trajectory inference and characterize dynamic features. CellChat was used to investigate intercellular interactions.

Results

OCTN2-deficient cardiomyocytes displayed transcriptomic alterations indicative of reduced contractility, developmental abnormalities, and fibrosis. The reduced expression of genes encoding troponin, myosin, and calcium ion transporters may underlie the observed decrease in contractility. Suppressed Wnt signaling and downregulated transcription factors associated with myocardial development suggest potential developmental disturbances in cardiomyocytes. Growth arrest-specific 6 (GAS6) secreted by TNNC1 high cardiomyocytes is implicated in myocardial inflammation and fibrosis. Macrophages-derived secreted phosphoprotein 1 (SPP1) promotes the activation of fibroblasts. Furthermore, there was a reduction in neuronal genes in the OCTN2-deficient group.

Conclusions

Our research has unveiled, for the first time, the responses of cardiomyocytes and alterations in the intercellular communication in PCD DCM, offering valuable insights for the precision treatment of this condition.

Human model of primary carnitine deficiency cardiomyopathy reveals ferroptosis as a novel mechanism

Primary carnitine deficiency (PCD) is an autosomal recessive monogenic disorder caused by mutations in SLC22A5. This gene encodes for OCTN2, which transports the essential metabolite carnitine into the cell. PCD patients suffer from muscular weakness and dilated cardiomyopathy. Two OCTN2-defective human induced pluripotent stem cell lines were generated, carrying a full OCTN2 knockout and a homozygous OCTN2 (N32S) loss-of-function mutation. OCTN2-defective genotypes showed lower force development and resting length in engineered heart tissue format compared with isogenic control. Force was sensitive to fatty acid-based media and associated with lipid accumulation, mitochondrial alteration, higher glucose uptake, and metabolic remodeling, replicating findings in animal models. The concordant results of OCTN2 (N32S) and -knockout emphasizes the relevance of OCTN2 for these findings. Importantly, genome-wide analysis and pharmacological inhibitor experiments identified ferroptosis, an iron- and lipid-dependent cell death pathway associated with fibroblast activation as a novel PCD cardiomyopathy disease mechanism.

Clinical Significance of Carnitine in the Treatment of Cancer: From Traffic to the Regulation

Metabolic reprogramming is a common hallmark of cancer cells. Cancer cells exhibit metabolic flexibility to maintain high proliferation and survival rates. In other words, adaptation of cellular demand is essential for tumorigenesis, since a diverse supply of nutrients is required to accommodate tumor growth and progression. Diversity of carbon substrates fueling cancer cells indicate metabolic heterogeneity, even in tumors sharing the same clinical diagnosis. In addition to the alteration of glucose and amino acid metabolism in cancer cells, there is evidence that cancer cells can alter lipid metabolism. Some tumors rely on fatty acid oxidation (FAO) as the primary energy source; hence, cancer cells overexpress the enzymes involved in FAO. Carnitine is an essential cofactor in the lipid metabolic pathways. It is crucial in facilitating the transport of long-chain fatty acids into the mitochondria for β-oxidation. This role and others played by carnitine, especially its antioxidant function in cellular processes, emphasize the fine regulation of carnitine traffic within tissues and subcellular compartments. The biological activity of carnitine is orchestrated by specific membrane transporters that mediate the transfer of carnitine and its derivatives across the cell membrane. The concerted function of carnitine transporters creates a collaborative network that is relevant to metabolic reprogramming in cancer cells. Here, the molecular mechanisms relevant to the role and expression of carnitine transporters are discussed, providing insights into cancer treatment.

A case of Fukuyama-type congenital muscular dystrophy with acute carnitine deficiency triggered by fever, vomiting, and gastrointestinal bleeding

BACKGROUND

Carnitine is essential for transporting long-chain fatty acids into mitochondria and promotes energy metabolism via β-oxidation of long-chain fatty acids. Although carnitine is also present in the peripheral blood, 98% of total carnitine is stored in muscle tissue. Neuromuscular diseases accompanied by muscle atrophy are likely to lead to secondary carnitine deficiency, owing to the reduced amount of total carnitine stored in the body.

CASE PRESENTATION

An 8-y-old Japanese boy with Fukuyama-type congenital muscular dystrophy accompanied by severe psychomotor retardation had been constantly bedridden, suffered from dysphagia, and had been fed through a gastrostomy tube since the age of 1 y. Regular oral carnitine supplementation (5 mg/kg/d of levocarnitine) was initiated at the age of 7 y, which increased serum carnitine value to within the normal range (serum total carnitine concentration, 58.5-60.9 μmol/L; acylcarnitine concentration, 45.8-55.0 μmol/L; free carnitine concentration, 5.9-12.7 μmol/L). He developed a fever, vomiting, and gastrointestinal bleeding at the age of 8 y. He fell into a coma and visited an emergency room 12 h later. Hypoglycemia and hypocarnitinemia (serum total carnitine concentration, 3.7 μmol/L; acylcarnitine concentration, 2.9 μmol/L; free carnitine concentration, 0.8 μmol/L; acyl-to-free carnitine ratio, 3.6) were observed, and he was found to be negative for urinary ketone bodies.

CONCLUSIONS

Neuromuscular diseases accompanied by muscle atrophy may lead to acute carnitine deficiency, even if the serum carnitine concentration is within the normal range before onset. During sick days, it may be necessary to modify a patient's treatment, such as increasing both oral supplementation and intravenous administration of carnitine.

Electrocardiographic and Echocardiographic Features of Carnitine-Deficient Animal Model

Primary systemic carnitine deficiency (CDSP) is a rare disease that can lead to sudden cardiac death (SCD). Meanwhile, cardiac manifestations had been widely reported in CDSP cases. Researches on phenotype and mechanism are needed imperatively to evaluate the influence of carnitine deficiency on cardiovascular system. We induce an intraperitonealinjected carnitine deficiency mouse model and a transgenic mouse model created by CRISPR/Cas-mediated genome engineering to observe the ECG and echocardiography parameters to explore the cardiac pathophysiological features in carnitine deficiency. In female drug-induced carnitine-deficient mice, the tendency of shortened QTc interval existed in experimental groups compared with the control group (P<0 05). Statistically significant differences in QTc interval existed in low-dose as well as high-dose groups and control (P<0 05). The same rule appeared in heart rate (HR) and T wave duration (P<0 05). After 8 weeks of continuous injection, HR, left ventricular ejection fraction (LVEF) and left ventricular fraction shortening (LVFS) in low-dose group, HR as well as LVPWd in high-dose group increased significantly compared with the control (all P<0 05). In male drug-induced carnitine deficient mice, the tendency of shortened QTc interval also existed in experimental groups compared with the control group (P<0 05). Statistically significant differences in QTc interval existed in low-dose group and control (P<0 05). Compared with the control, PR interval declined significantly in high-dose group (P<0 05). After 8 weeks of continuous injection, no cardiac functional indexes in experimental groups altered significantly compared with the control (all P>0 05) were found. In transgenic mice, free carnitine (C0) level statistically decreased (P<0 05) compared with the wild-type (WT) mice. There was no statistical difference between mice carried two single heterozygote (P>0 05). However, C0 level between compound heterozygote and single heterozygote was statistically significant (P>0 05). Moreover, there were no significant differences recorded compared with WT in ECG and echocardiography (P>0 05). This study suggested that carnitine deficiency had impact on cardiac function and structure in some situations. We summarized the ECG and echocardiography features of carnitine-deficient mice model and build the first transgenic animal model imitating the pathogenic genotype in human CDSP patients, which provide a foundation for further research on pathophysiological and molecular mechanism.

Screening for newborn fatty acid oxidation disorders in Chongqing and the follow-up of confirmed children

OBJECTIVE

To investigate the incidence, clinical characteristics, gene mutations and prognosis of fatty acid oxidation disorders (FAOD) in newborns in Chongqing.

METHODS

Blood samples were collected from 35 374 newborns for screening of FAOD in the Neonatal Screening Center of Women and Children's Hospital of Chongqing Medical University from July 2020 to February 2022. The acylcarnitine spectrum was detected by tandem mass spectrometry, the positive children in primary screening were recalled within 2 weeks, and the diagnosis of FAOD was confirmed by urine organic acid measurement, blood biochemistry testing and genetic analysis. The confirmed children were given early intervention, treatment and followed-up.

RESULTS

Among 35 374 newborns, there were 267 positive children in primary screening, with a positive rate of 0.75%. Five children with FAOD were diagnosed by gene detection, with an incidence rate of 1/7075. Among them, there were 3 cases of primary carnitine deficiency (PCD, 1/11 791), 1 case of short-chain acyl-CoA dehydrogenase deficiency (SCADD, 1/35 374) and 1 case of very long-chain acyl-CoA dehydrogenase deficiency (VLCADD, 1/35 374). The c.1400C>G and c.338G>A were the common mutations of SLC22A5 gene in 3 children with PCD, while c.621G>T was a novel mutation. There were no clinical manifestations during the follow-up period in 2 children with supplementation of L-carnitine. Another child with PCD did not follow the doctor's advice of L-carnitine treatment, and had acute attack at the age of 6 months. The child recovered after treatment, and developed normally during the follow-up. The detected ACADS gene mutations were c.417G>C and c.1054G>A in child with SCADD, who showed normal intelligence and physical development without any clinical symptoms. The mutations of ACADVL gene were c.1349G>A and c.1843C>T in child with VLCADD, who showed acute attack in the neonatal period and recovered after treatment; the child was fed with milk powder rich in medium-chain fatty acids and had normal development during the follow-up.

CONCLUSIONS

The incidence of FAOD in Chongqing area is relatively high. PCD is the most common type, and the clinical phenotype of VLCADD is serious. After early diagnosis through neonatal screening, standardized treatment and management is followed, most of FAOD children can have good prognosis.

Cardiologic evaluation of Turkish mitochondrial fatty acid oxidation disorders

BACKGROUND

Mitochondrial fatty acid oxidation disorders (FAODs) cause impairment in energy metabolism and can lead to a spectrum of cardiac pathologies including cardiomyopathy and arrhythmias. The frequency of underlying cardiac pathologies and the response to recommended treatment in FAODs was investigated.

METHODS

Sixty-eight children (35 males, 33 females) with the diagnosis of a FAOD were included in the study. Cardiac function was evaluated with 12-lead standard electrocardiography, echocardiography, and 24 h Holter monitoring.

RESULTS

Forty-five patients (66%) were diagnosed after disease symptoms developed and 23 patients (34%) were diagnosed in the pre-symptomatic period. Among symptomatic patients (n: 45), cardiovascular findings were detected in 18 (40%) patients, including cardiomyopathy in 14 (31.1%) and conduction abnormalities in 4 (8.8%) patients. Cardiac symptoms were more frequently detected in primary systemic carnitine deficiency (57.1%). Patients with multiple acyl-CoA dehydrogenase, long-chain 3-hydroxyacyl-CoA dehydrogenase, and mitochondrial trifunctional protein deficiencies also had an increased frequency of cardiac symptoms. Patients with medium-chain acyl-CoA dehydrogenase, very long-chain acyl-CoA dehydrogenase, and carnitine palmitoyltransferase I deficiencies had a lower prevalence of cardiac symptoms both during admission and during clinical follow up. Cardiomyopathy resolved completely in 8/14 (57%) patients and partially in 2/14 (14.3%) patients with treatment. Two patients with cardiomyopathy died in the newborn period; cardiomyopathy persisted in 1 (7.1%) patient with very long-chain acyl-CoA dehydrogenase deficiency.

CONCLUSION

Early diagnosis, treatment and follow up made a significant contribution to the improvement of cardiac symptoms of patients with FAODs.

Diagnosis, genetic characterization and clinical follow up of mitochondrial fatty acid oxidation disorders in the new era of expanded newborn screening: A single centre experience

Introduction

Mitochondrial fatty acid oxidation disorders (FAODs) are a heterogeneous group of hereditary autosomal recessive diseases included in newborn screening (NBS) program in Italy. The aim of this study was to analyse FAODs cases, identified either clinically or by NBS,for clinical and genetic characterization and to evaluate a five years' experience of NBS, in the attempt to figure out the complexity of genotype-phenotype correlation and to confirm the clinical impact of NBS in our centre experience.

Materials and methods

We analysed FAODs patients diagnosed either by NBS or clinically, followed since February 2014 to April 2019 at the Regional Screening Centre and Inherited Metabolic Diseases Unit of Verona. Diagnosis was confirmed by plasma acylcarnitines, urinary organic acids, enzymatic and genetic testing. For not clear genotypes due to the presence of variants of uncertain significance, in silico predictive tools have been used as well as enzymatic activity assays. Patients underwent clinical, nutritional and biochemical follow up.

Results

We diagnosed 30 patients with FAODs. 20 by NBS: 3 CUD, 6 SCADD, 5 MCADD, 4 VLCADD, 2 MADD. Overall incidence of FAODs diagnosed by NBS was 1:4316 newborns. No one reported complications during the follow up period. 10 patients were diagnosed clinically: 2 CUD, 2 CPT2D, 1 VLCADD, 5 MADD. Mean age at diagnosis was 29.3 years. Within this group, complications or symptoms were reported at diagnosis, but not during follow-up. 12 mutations not previously reported in literature were found, all predicted as pathogenic or likely pathogenic.

Discussion and conclusions

Our study highlighted the great phenotypic variability and molecular heterogeneity of FAODs and confirmed the importance of a tailored follow up and treatment. Despite the short duration of follow up, early identification by NBS prevented diseases related complications and resulted in normal growth and psycho-motor development as well.

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Early identification by newborn screening prevents disease related complications.

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Newborn screening is changing prevalence clinical and molecular heterogeneity of FAODs.

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Genotype-phenotype correlation helps to achieve personalized follow-up and treatment.

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Enzymatic assay may be pivotal in predicting phenotype and symptoms severity.

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Diagnosis on clinical grounds is anyway important to change disease course.

Primary carnitine deficiency - diagnosis after heart transplantation: better late than never!

Background

Primary carnitine deficiency due to mutations in the SLC22A5 gene is a rare but well-treatable metabolic disorder that puts patients at risk for metabolic decompensations, skeletal and cardiac myopathy and sudden cardiac death.

Results

We report on a 7-year-old boy diagnosed with primary carnitine deficiency 2 years after successful heart transplantation thanks his younger sister’s having been identified via expanded newborn screening during a pilot study evaluating an extension of the German newborn screening panel.

Conclusion

As L-carnitine supplementation can prevent and mostly reverse clinical symptoms of primary carnitine deficiency, all patients with cardiomyopathy should be investigated for primary carnitine deficiency even if newborn screening results were unremarkable.

Primary Carnitine Deficiency: A Rare, Reversible Metabolic Cardiomyopathy

A 24-year-old female with a diagnosis of primary carnitine deficiency, a rare inherited metabolic disorder predominantly described in the paediatric literature that causes cardiomyopathy, presented for evaluation after three months of nonadherence with prescribed carnitine therapy. Initial echocardiography demonstrated severe left ventricular dilation (104 ml/m²) (normal < 76 ml/m²) with moderate systolic dysfunction (ejection fraction 40%) and severe right ventricular dilation with mild systolic dysfunction. Carnitine replacement was commenced, and a cardiac magnetic resonance imaging (MRI) performed five days later demonstrated dramatic improvement in biventricular function with normalization of left and right ventricular systolic function. To our knowledge, this is only the second case describing the rapid reversal of cardiomyopathy in an adult patient with this rare condition.

Lipid storage myopathies: Current treatments and future directions

Lipid storage myopathies (LSMs) are a heterogeneous group of genetic disorders that present with abnormal lipid storage in multiple body organs, typically muscle. Patients can clinically present with cardiomyopathy, skeletal muscle weakness, myalgia, and extreme fatigue. An early diagnosis is crucial, as some LSMs can be managed by simple nutraceutical supplementation. For example, high dosage l-carnitine is an effective intervention for patients with Primary Carnitine Deficiency (PCD). This review discusses the clinical features and management practices of PCD as well as Neutral Lipid Storage Disease (NLSD) and Multiple Acyl-CoA Dehydrogenase Deficiency (MADD). We provide a detailed summary of current clinical management strategies, highlighting issues of high-risk contraindicated treatments with case study examples not previously reviewed. Additionally, we outline current preclinical studies providing disease mechanistic insight. Lastly, we propose that a number of other conditions involving lipid metabolic dysfunction that are not classified as LSMs may share common features. These include Neurofibromatosis Type 1 (NF1) and autoimmune myopathies, including Polymyositis (PM), Dermatomyositis (DM), and Inclusion Body Myositis (IBM).

Carnitine-related hypoglycemia caused by 3 days of pivalate antibiotic therapy in a patient with severe muscular dystrophy: a case report

BACKGROUND

Long-term treatment with antibiotics containing pivalic acid may decrease serum carnitine concentration and can sometimes be associated with severe hypoglycemia and encephalopathy in infants. Little has been reported, however, on severe hypocarnitinemia induced by acute administration in older children.

CASE PRESENTATION

We describe a 6-year-old Japanese girl with Fukuyama-type congenital muscular dystrophy who lost consciousness after 3 days of treatment with an antibiotic containing pivalic acid (cefditoren pivoxil). Investigations at the onset of unconsciousness revealed hypoglycemia (free plasma glucose concentration: 31 mg/dL) and hypocarnitinemia (serum free carnitine concentration: 6.2 μmol/L). Intravenous administration of glucose rapidly improved her symptoms without any complications. Serum free carnitine concentration was 29.0 μmol/L immediately prior to the initiation of cefditoren pivoxil. Computed tomography scanning showed severe peripheral skeletal muscle atrophy, indicating the likelihood of decreased carnitine stores in skeletal muscle.

CONCLUSIONS

Although serum carnitine concentration can appear deceptively normal, skeletal muscle carnitine stores can be reduced in patients with severe muscular atrophy. Even a short course of a pivalate-containing antibiotic can lead to life-threatening hypocarnitinemia in older children with severe muscular dystrophy.

Dilated Cardiomyopathy as the Only Clinical Manifestation of Carnitine Transporter Deficiency

The authors present a case of carnitine transporter deficiency, which was unmasked after an episode of respiratory distress resistant to treatment with bronchodilators. Chest radiograph showed cardiomegaly; electrocardiogram showed left ventricular hypertrophy and echocardiography revealed dilated cardiomyopathy. Heart failure therapy was initiated and metabolic screening was requested, as family history was indicative of inborn errors of metabolism. Very low levels of free carnitine and carnitine esters in blood were found and genetic testing confirmed the diagnosis of carnitine transporter deficiency. After oral supplementation with L-carnitine, symptoms gradually ameliorated and heart function had fully recovered. Sequence analysis in the SLC22A5 gene revealed the missense mutation c.1319C > T (p.Th440Met) in homozygous state. Homozygous c.1319C > T (p.Th440Met) mutation has not been associated with a pure cardiac phenotype before.