Overview
Renal carnitine transport defect (CUD) is an autosomal recessive disorder caused by mutations in the SLC22A5 gene, leading to impaired carnitine uptake and affecting fatty acid oxidation. It typically manifests in infancy with symptoms like muscle weakness, cardiomyopathy, and hypoketotic hypoglycemia, but can also present later with recurrent metabolic crises 12.Diagnosis
Key Diagnostic Criteria: Profound muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, and characteristic EKG findings in infants 1.
Recommended Tests: Newborn screening via tandem mass spectrometry for low free carnitine levels; confirmatory tests include dried blood spot acylcarnitine profiling and SLC22A5 gene mutation analysis 2.
False Positives/Negatives: Transplacental transfer of carnitine from affected mothers can cause false negatives in newborn screening; increased fractional excretion of free carnitine in urine may indicate CUD in false negatives 1.
Genetic Analysis: Identification of mutations, including those in the 5' UTR region of SLC22A5, is crucial for diagnosis 1.Management
First-Line Treatment: High-dose carnitine supplementation (50-100 mg/kg/day) to correct carnitine deficiency and manage symptoms 2.
Adjunctive Measures: Close monitoring of cardiac function, especially in cases with cardiomyopathy, and prompt intervention for metabolic crises 2.Special Populations
Pregnancy: Asymptomatic maternal CUD can lead to transient carnitine deficiency in newborns; maternal carnitine supplementation is recommended 2.
Pediatrics: Early diagnosis and treatment are critical to prevent severe complications such as cardiomyopathy and recurrent hypoglycemia 12.Key Recommendations
Perform newborn screening for low free carnitine levels and confirm with acylcarnitine profiling and SLC22A5 gene analysis to diagnose CUD (Evidence: Strong 2).
Initiate high-dose carnitine supplementation (50-100 mg/kg/day) in diagnosed patients to manage carnitine deficiency and associated symptoms (Evidence: Moderate 2).
Screen and treat affected mothers with carnitine supplementation to prevent transient carnitine deficiency in newborns (Evidence: Expert opinion 2).References
1 Verbeeten KC, Lamhonwah AM, Bulman D, Faghfoury H, Chakraborty P, Tein I et al.. Carnitine uptake defect due to a 5'UTR mutation in a pedigree with false positives and false negatives on Newborn screening. Molecular genetics and metabolism 2020. link
2 Lee NC, Tang NL, Chien YH, Chen CA, Lin SJ, Chiu PC et al.. Diagnoses of newborns and mothers with carnitine uptake defects through newborn screening. Molecular genetics and metabolism 2010. link