Newborn screening for primary carnitine deficiency using a second-tier genetic test.

OBJECTIVES: Newborn screening (NBS) for primary carnitine deficiency (PCD) exhibits suboptimal performance. This study proposes a strategy to enhance the efficacy of second-tier genetic screening by adjusting the cutoff value for free carnitine (C0). METHODS: Between January 2021 and December 2022, we screened 119,898 neonates for inborn metabolic disorders. Neonates with C0 levels below 12 µmol/L were randomly selected for second-tier genetic screening, employing a novel matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assay. RESULTS: In total, 2,515 neonates with C0 <12 µmol/L underwent further screening, including 206 neonates with C0 <8.5 µmol/L and 320 neonates with 8.5G, accounting for 25 % (7/28) of allelic frequencies. CONCLUSIONS: A novel MALDI-TOF MS assay targeting 21 SLC22A5 variants in a Chinese population was successfully established. This assay exhibits a high detection and diagnostic rate, making it suitable for population-based genetic screening. Combined genetic screening is recommended to enhance the efficiency of PCD-NBS.

Left ventricular noncompaction cardiomyopathy and short QT syndrome due to primary carnitine deficiency.

We report the case of a 13-year-old female patient presenting with presyncope and palpitations. Her electrocardiogram revealed an abbreviation of the rate-corrected QT interval with imaging showing significant left ventricular dysfunction. Carnitine levels were measured as part of her diagnostic workup, discovering a rare, reversible cause of short QT syndrome (SQTS) and associated cardiomyopathy-primary carnitine deficiency (PCD) caused by a homozygous mutation in the SLC22A5 gene, leading to an in-frame deletion mutation (NP_003051.1:p.Phe23del) affecting the organic cation transporter 2 (OCTN2) protein. Following the treatment with oral carnitine supplementation, her QT interval returned to within the normal range with significant improvement in left ventricular function.

Primary Carnitine Deficiency as a Treatable Cause of Heart Failure in Young Patients.

Non-ischemic dilated cardiomyopathy is the most common subgroup of heart failure in young adults. Several metabolic defects could be the underlying etiology in these young heart failure patients. However, most cases are considered idiopathic. Primary carnitine deficiency is an overlooked inherited metabolic disease causing cardiomyopathy in these patients. Oral carnitine replacement therapy could prevent primary carnitine deficiency patients from progressing to advanced heart failure and life-threatening arrhythmias. In this case report, we present an index primary carnitine deficiency case and his brother's diagnosis and successful treatment period to draw attention to primary carnitine deficiency as a treatable cause of heart failure in young adults.

Lenvatinib causes reduced expression of carnitine/organic cation transporter 2 and carnitine deficiency in the skeletal muscle of rats.

Lenvatinib, an oral tyrosine kinase inhibitor, is widely used to treat several types of advanced cancers but often causes muscular adverse reactions. Although carnitine supplementation may prevent these effects, the mechanism underlying lenvatinib-induced skeletal muscle impairment remains poorly understood. To this end, we aimed to investigate the impact of lenvatinib on carnitine disposition in rats. Once-daily administration of lenvatinib repeated for two weeks did not affect urinary excretion or serum concentration of carnitines throughout the treatment period but ultimately decreased the L-carnitine content in the skeletal muscle. The treatment decreased the expression of carnitine/organic cation transporter (OCTN) 2, a key transporter of carnitine, in skeletal muscle at the protein level but not at the mRNA level. In cultured C2C12 myocytes, lenvatinib inhibited OCTN2 expression in a dose-dependent manner at the protein level. Furthermore, lenvatinib dose-dependently decreased the protein levels of carnitine-related genes, adenosine triphosphate content, mitochondrial membrane potential, and markers of mitochondrial function in vitro. These results reveal the deleterious effects of lenvatinib on OCTN2 expression, carnitine content, and mitochondrial function in skeletal muscle that may be associated with muscle toxicity.

Rare case of primary carnitine deficiency presenting as acute liver failure.

Systemic primary carnitine deficiency (PCD) is an autosomal recessive disorder caused by mutations in the SLC22A5 gene that encodes carnitine transporter, OCTN2. Transporter deficiency leads to defective fatty acid oxidation. Signs and symptoms ranging from liver injury in children to cardiomyopathy and skeletal myopathy in adults, manifest during periods of stress and fasting. Though acute liver failure is infrequently described, young children presenting as acute liver failure should be screened for fatty acid oxidation defects including PCD by testing plasma for amino acids and further confirmed by genetic sequencing. Early identification and treatment using L-carnitine is lifesaving. Our patient presented as acute liver failure and diagnosis of PCD was confirmed by metabolic screening and genetic sequencing. He responded to the treatment.

Evaluation of the relationship between serum carnitine levels and intradialytic complications in children with kidney failure.

BACKGROUND: Carnitine plays a crucial role in the metabolism of fatty acids as well as energy production. Previous research has suggested a significant decrease in carnitine levels in patients with kidney failure and those undergoing hemodialysis. Therefore, we designed this study to assess the prevalence and characteristics of carnitine deficiency and its association with hemodialysis complications in the pediatric population. METHODS: This research was a pilot study of 29 children undergoing hemodialysis. Before hemodialysis, a 5-mL blood sample was drawn from each patient through a peripheral vein to measure serum-free carnitine levels, complete blood count with differential, blood urea nitrogen (BUN), creatinine, and electrolytes. Each patient was observed for intradialytic complications, including muscle cramps and hypotension, during 12 sessions of hemodialysis. RESULTS: We included 26 participants with a mean age of 14.23 years undergoing hemodialysis. Carnitine deficiency was revealed in 54.8% of our participants. Also, there was no significant correlation between carnitine deficiency and age, gender, and BUN levels (P = 0.698, P = 0.43, and P > 0.05, respectively). Intradialytic complications, including episodes of hypotension and muscle cramps, were more frequent in patients with carnitine deficiency (P = 0.02, P = 0.01, respectively). Other reasons for muscle cramps, such as fluid overload, nutritional status, dialysis regimen, and other important lab results (phosphorus, magnesium, etc.), were ruled out. CONCLUSION: In conclusion, we found a higher prevalence of carnitine deficiency in pediatric hemodialysis patients. Carnitine deficiency was significantly associated with increased intradialytic symptoms, including muscle spasms and hypotension. Our results could support a potential role of carnitine supplementation in pediatric patients with kidney failure for controlling intradialytic complications, but this requires further investigation. A higher resolution version of the Graphical abstract is available as Supplementary information.

Association between Levocarnitine Treatment and the Change in Knee Extensor Strength in Patients Undergoing Hemodialysis: A Post-Hoc Analysis of the Osaka Dialysis Complication Study (ODCS).

Carnitine deficiency is prevalent in patients undergoing hemodialysis, and it could result in lowered muscle strength. So far, the effect of treatment with levocarnitine on lower limb muscle strength has not been well described. This observational study examined the association between treatment with levocarnitine with the change in knee extensor strength (KES) in hemodialysis patients. Eligible patients were selected from the participants enrolled in a prospective cohort study for whom muscle strength was measured annually. We identified 104 eligible patients for this analysis. During the one-year period between 2014 to 2015, 67 patients were treated with intravenous levocarnitine (1000 mg per shot, thrice weekly), whereas 37 patients were not. The change in KES was significantly higher (p = 0.01) in the carnitine group [0.02 (0.01-0.04) kgf/kg] as compared to the non-carnitine group [-0.02 (-0.04 to 0.01) kgf/kg]. Multivariable-adjusted regression analysis showed the positive association between the change in KES and the treatment with levocarnitine remained significant after adjustment for the baseline KES and other potential confounders. Thus, treatment with intravenous levocarnitine was independently and positively associated with the change in KES among hemodialysis patients. Further clinical trials are needed to provide more solid evidence.

Clinical characteristics of primary carnitine deficiency: A structured review using a case-by-case approach.

A broad spectrum of signs and symptoms has been attributed to primary carnitine deficiency (PCD) since its first description in 1973. Advances in diagnostic procedures have improved diagnostic accuracy and the introduction of PCD in newborn screening (NBS) programs has led to the identification of an increasing number of PCD patients, including mothers of screened newborns, who may show a different phenotype compared to clinically diagnosed patients. To elucidate the spectrum of signs and symptoms in PCD patients, we performed a structured literature review. Using a case-by-case approach, clinical characteristics, diagnostic data, and mode of patient identification were recorded. Signs and symptoms were categorized by organ involvement. In total, 166 articles were included, reporting data on 757 individual patients. In almost 20% (N = 136) of the cases, the diagnosis was based solely on low carnitine concentration which we considered an uncertain diagnosis of PCD. The remaining 621 cases had a diagnosis based on genetic and/or functional (ie, carnitine transporter activity) test results. In these 621 cases, cardiac symptoms (predominantly cardiomyopathy) were the most prevalent (23.8%). Neurological (7.1%), hepatic (8.4%), and metabolic (9.2%) symptoms occurred mainly in early childhood. Adult onset of symptoms occurred in 16 of 194 adult patients, of whom 6 (3.1%) patients suffered a severe event without any preceding symptom (five cardiac events and one coma). In conclusion, symptoms in PCD predominantly develop in early childhood. Most newborns and mothers of newborns detected through NBS remain asymptomatic. However, though rarely, severe complications do occur in both groups.

Relationship between Carnitine Deficiency and Tyrosine Kinase Inhibitor Use in Patients with Chronic Myeloid Leukemia.

BACKGROUND: Some chemotherapeutic agents cause carnitine deficiency, which causes general fatigue. However, there is no study on carnitine deficiency in patients with chronic myeloid leukemia (CML) during tyrosine kinase inhibitor (TKI) therapy. OBJECTIVE: In this study, we investigated carnitine concentrations in patients with CML receiving TKI therapy. METHOD: This study included patients with well-controlled CML. Total carnitine and free carnitine concentrations were evaluated using the enzyme cycling method. The brief fatigue inventory (BFI) and cancer fatigue scale (CFS) were used to assess general fatigue developed during TKI therapy. RESULTS: Fifty-five patients on TKI therapy were included. Of these, 12 (21.8%) patients had low free carnitine concentrations. Free carnitine concentrations were higher in men than in women. Younger age was closely associated with lower free carnitine concentrations. TKI type, TKI dose, treatment response, or therapy duration were not associated with free carnitine concentrations. None of the scores (the global fatigue score with the BFI and CFS score) correlated with carnitine concentrations. Concentrations of free carnitine in patients in the treatment-free remission group were slightly higher than those in the TKI group, with only 9.1% having a low concentration of free carnitine. CONCLUSION: Carnitine deficiency is probably not a major cause of general fatigue but may occur in patients with CML receiving TKI therapy.

Hypoglycemia Due to Acquired Carnitine Deficiency in a Pediatric Patient Receiving Chemotherapy.

We describe a 21-month-old male with relapsed clear cell sarcoma of the kidney receiving enteral nutrition who experienced recurrent, ketotic hypoglycemia. During relapse therapy, he had recurrent hypoglycemia episodes, in the setting of hematochezia and diarrhea. Evaluation revealed low carnitine levels. He received supplementation with oral levocarnitine throughout the remainder of treatment, resulting in normalization of serum carnitine levels and no further hypoglycemia. We believe adverse effects of the chemotherapy on his single kidney and gastrointestinal insult resulted in hypoglycemia and carnitine deficiency. Our case highlights that carnitine deficiency should be considered when acute onset hypoglycemia without obvious cause occurs.

Altered mitochondrial metabolism in peripheral blood cells from patients with inborn errors of ß-oxidation.

Inborn errors of mitochondrial fatty acid oxidation (FAO), such as medium-chain acyl-CoA dehydrogenase deficiency (MCAD) and very long-chain acyl-CoA dehydrogenase deficiency (VLCAD) affects cellular function and whole-body metabolism. Carnitine uptake deficiency (CUD) disturbs the transportation of fatty acids into the mitochondria, but when treated is a mild disease without significant effects on FAO. For improved clinical care of VLCAD in particular, estimation of FAO severity could be important. We have investigated whether the oxygen consumption rate (OCR) of peripheral blood mononuclear cells (PBMCs) obtained from patients with MCAD, VLCAD, and CUD can be used to study cellular metabolism in patients with FAO defects and to determine the severity of FAO impairment. PBMCs were isolated from patients with VLCAD (n = 9), MCAD (n = 5-7), and CUD (n = 5). OCR was measured within 6-hours of venous puncture using the Seahorse XFe96. The PBMCs were exposed to glucose alone or with caprylic acid (C8:0) or palmitic acid (C16:0). OCR was significantly lower in cells from patients with ß-oxidation deficiencies (MCAD and VLCAD) compared to CUD at basal conditions. When exposed to C16:0, OCR in VLCAD cells was unchanged, whereas OCR in MCAD cells increased but not to the levels observed in CUD. However, C8:0 did not increase OCR, as would be expected, in VLCAD cells. There was no clear relationship between clinical severity level and OCR. In patients with ß-oxidation deficiencies, changes of mitochondrial respiration in PBMCs are detectable, which indicate that PBMCs have translational potential for studies of ß-oxidation defects. However, further studies are warranted.

Biochemical and genetic characteristics of patients with primary carnitine deficiency identified through newborn screening.

BACKGROUND: Primary carnitine deficiency (PCD) is an autosomal recessive disorder of carnitine transportation that leads to impaired fatty acid oxidation. Large-scale studies on newborn screening (NBS) for PCD are limited. This study aimed to investigate the biochemical and genetic characteristics of patients with PCD detected through NBS. RESULTS: A total of 548 247 newborns were screened for PCD between January 2014 and June 2021; 1714 newborns with low free carnitine (C0) levels were called back and 49 patients were diagnosed with PCD. The latest incidence rate in Quanzhou, China, was estimated to be 1 in 11 189 newborns. NBS results showed that the 49 patients had varying degrees of decreased C0 levels, whereas seven patients exhibited normal C0 levels during the recall review. All patients harbored biallelic pathogenic variants of the SLC22A5 gene. Nineteen distinct SLC22A5 variants were detected in these 49 patients, and most of the detected variants were clustered in exons 1, 4, and 7. The top eight variants had an allele frequency of 86.73%. The most common variant was c.760C > T (p.R254*) with an allele frequency of 31.63%, followed by c.51C > G (p.F17L) (17.35%) and c.1400C > G (p.S467C) (16.33%). The C0 level of patients with the N/N genotype was significantly lower than that of the M/M group. The C0 levels of patients with genotypes of R254*/R254* and R254*/F17L were far lower than those of patients with the R254*/S467C genotype. CONCLUSIONS: This study presented more than 500,000 NBS data with the latest incidence of 1:11 189 in the Quanzhou area. The SLC22A5 variant spectrum in the selected southern Chinese population has been updated. Patients with null variants were associated with low C0 levels. Combining NBS with genetic testing is critical to improve screening efficiency because patients with PCD may have normal C0 levels during NBS and recall review.

[Analysis of metabolic profile and genetic variants for newborns with primary carnitine deficiency from Guangxi].

OBJECTIVE: To analyze the metabolic profile and genetic variants for newborns with primary carnitine deficiency (PCD) from Guangxi, China. METHODS: From January 2014 to December 2019, 400 575 newborns from the jurisdiction of Guangxi Zhuang Autonomous Region Newborn Screening Center were subjected to tandem mass spectrometry (MS/MS) analysis. Newborns with positive results for PCD and their mothers were recalled for retesting. Those who were still positive were subjected to sequencing of the SLC22A5 gene. RESULTS: Twenty-two newborns and 9 mothers were diagnosed with PCD, which gave a prevalence rate of 1/18 208. Sequencing of 18 newborns and 4 mothers have identified 14 types of SLC22A5 gene variants, with the common ones including c.51C>G (10/44, 22.7%), c.1195C>T (9/44, 20.5%) and c.1400C>G (7/44, 15.9%), The c.517delC(p.L173Cfs*3) and c.1031C>T(p.T344I) were unreported previously and predicted to be pathogenic (PVS1+PM2_supporting+PM3+PP4) and likely pathogenic (PM1+PM2_supporting+PM3+PP3+PP4) based on the American College of Medical Genetics and Genomics standards and guidelines. CONCLUSION: c.51C>G, c.1195C>T and c.1400C>G are the most common variants underlying PCD in Guangxi.

3-Methylglutaconic aciduria in carriers of primary carnitine deficiency.

The etiology of secondary 3-methylglutaconic aciduria (3-MGA-uria) is not well understood although is thought to be a marker of mitochondrial dysfunction. For this reason, suspicion for a secondary 3-MGA-uria often leads to an extensive clinical and laboratory work-up for mitochondrial disease, although in many cases evidence for mitochondrial dysfunction is never found. 3-methylglutaconic aciduria in healthy individuals without known metabolic disease has not been well described. Here, we describe clinical and biochemical features of 23 individuals evaluated at the Greenwood Genetic Center for low plasma free carnitine reported on newborn screening. Of the 23 individuals evaluated, four individuals were diagnosed with primary carnitine deficiency, 16 were identified as carriers for primary carnitine deficiency, and three individuals were determined to be unaffected non-carriers based on molecular and biochemical testing. Elevated 3-MGA (>20 mmol/mol of creatinine) was identified in nine carriers of primary carnitine deficiency, while all unaffected non carriers and all affected individuals with primary carnitine deficiency had a normal 3-MGA level (<20 mmol/mol of creatinine). Average 3-MGA among all carriers was 39.66 mmol/mol of creatinine. Average plasma free carnitine in among all carriers (n = 16) was 13.87 µm/L, and average plasma free carnitine was not significantly different between carriers with and those without elevated 3-MGA (p = 0.66). In summary, we describe elevated 3-MGA as a discriminatory feature in nine healthy carriers of primary carnitine deficiency. Our findings suggest that heterozygosity for pathogenic alterations on SLC22A5 should be considered in the differential for individuals with persistent 3-MGA-uria of unclear etiology.

General anesthesia with cisatracurium and sevoflurane for a patient with primary carnitine deficiency receiving L-carnitine therapy: A case report.

RATIONALE: Lipid storage myopathies (LSMs) are a series of genetic disorders of lipid metabolism predominantly affecting muscle. The low incidence and lethal properties of this disease make anesthesia experience limited in such patients. Among all etiologies of LSMs, primary carnitine deficiency (PCD) is now considered highly treatable by early administration of L-carnitine, though it remains unclear whether L-carnitine is effective enough to protect diseased muscle against conventionally used neuromuscular blocking agents (NMBAs) during general anesthesia. Currently, no data are available concerning possible prolonged muscle weakness in these cases. PATIENT CONCERNS: This case presents a 43-year-old female who was diagnosed with a PCD-induced LSM 3 years ago due to fatigability and exertional myalgias and has been treated with L-carnitine ever since. At the time of this report, she was admitted for uterine fibroids and scheduled for selective open gynecologic surgery under general anesthesia. DIAGNOSIS: The patient's diagnosis of PCD-induced LSM was based on the clinical features, muscle biopsy, and diminished organic cation/carnitine transporter 2 (OCTN2) transporter activity in the patient's skin fibroblasts. INTERVENTIONS: L-carnitine was taken by the patient until the morning of surgery. General anesthesia with cisatracurium and sevoflurane was selected as the anesthetic plan during the operation. The train-of-four (TOF) test was adopted as additional monitoring, particularly to track the recovery of neuromuscular function. OUTCOMES: The patient was extubated successfully following a spontaneously restored TOF ratio (TOFR) of 0.9. Nonetheless, we recorded a prolonged efficacy of cisatracurium in the clinical duration and the recovery time with TOFRs of 0.7 and 0.9, respectively. LESSONS: The conventional dose of cisatracurium combined with a low dose of sevoflurane can be safely used in patients with LSMs without additional anesthetic risks. Meanwhile, continuous TOF monitoring is recommended to perform high-quality anesthesia.

L-carnitine supplementation for muscle weakness and fatigue in children with neurofibromatosis type 1: A Phase 2a clinical trial.

Reduced muscle tone, muscle weakness, and physical fatigue can impact considerably on quality of life for children with neurofibromatosis type 1 (NF1). Human muscle biopsies and mouse models of NF1 deficiency in muscle show intramyocellular lipid accumulation, and preclinical data have indicated that L-carnitine supplementation can ameliorate this phenotype. The aim of this study is to examine whether daily L-carnitine supplementation is safe and feasible, and will improve muscle strength and reduce fatigue in children with NF1. A 12-week Phase 2a trial was conducted using 1000 mg daily oral levocarnitine tartrate supplementation. Recruited children were between 8 and 12 years old with a clinical diagnosis of NF1, history of muscle weakness and fatigue, and naïve to L-carnitine. Primary outcomes were safety (self-reporting, biochemical testing) and compliance. Secondary outcomes included plasma acylcarnitine profiles, functional measures (muscle strength, long jump, handwriting speed, 6-minute-walk test [6MWT]), and parent-reported questionnaires (PedsQL™, CBCL/6-18). Six children completed the trial with no self-reported adverse events. Biochemical tests for kidney and liver function were normal, and the average compliance was 95%. Plasma acylcarnitine levels were low, but within a range not clinically linked to carnitine deficiency. For strength measures, there was a mean 53% increase in dorsiflexion strength (95% confidence interval [CI] 8.89-60.75; p = 0.02) and mean 66% increase in plantarflexion strength (95% CI 12.99-134.1; p = 0.03). In terms of muscle performance, there was a mean 10% increase in long jump distance (95% CI 2.97-16.03; p = 0.01) and 6MWT distance (95% CI 5.88-75.45; p = 0.03). Comparison with the 1000 Norms Project data showed a significant improvement in Z-score for all of these measures. Parent reports showed no negative impact on quality of life, and the perceived benefits led to the majority of individuals remaining on L-carnitine after the study. Twelve weeks of L-carnitine supplementation is safe and feasible in children with NF1, and a Phase 3 trial should confirm the efficacy of treatment.