Mild carnitine uptake defect due to a novel homozygous mutation in the SLC22A5 gene detected by newborn screening

Carnitine uptake defect (CUD) is a rare autosomal recessive disorder caused by pathogenic variants in the SLC22A5 gene, resulting in primary carnitine transporter (OCTN2) deficiency and disturbed fatty acid oxidation. Patients may present in infancy with hypoketotic hypoglycemia, metabolic crisis, muscle weakness, cardiomyopathy, or sudden death, while some may remain asymptomatic even if not treated. We present a patient detected by newborn screening (NBS) who harbored a previously unreported homozygous variant in the SLC22A5 gene. OCTN2 activity testing showed mild deficiency.