Tehran University of Medical Sciences Immunology and Genetics Journal 2645-4831 9 3 2026 07 19 240 240 Ehsan Khosh Nezhad Afkham Department of Pediatrics, School of Medicine; Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran 2026 07 02 2026 07 18 Systemic primary carnitine deficiency (SPCD) is a rare autosomal recessive metabolic disorder caused by mutations in the SLC22A5 gene, leading to defective carnitine transport and impaired fatty acid oxidation. Clinical presentations vary widely, from asymptomatic individuals detected via newborn screening to infants with severe multisystem involvement. Early recognition is critical; as timely L-carnitine supplementation can prevent life-threatening complications. We report a 5.5-month-old male infant, born to consanguineous parents, who presented with recurrent vomiting, lethargy, poor feeding, and abnormal movements suggestive of seizures. Physical examination revealed generalized hypotonia, nystagmus, hepatomegaly, peripheral edema, and respiratory distress. Laboratory workup demonstrated anemia, coagulopathy, elevated liver enzymes, hypertriglyceridemia, and markedly low plasma free carnitine. Cardiac evaluation showed mild left ventricular hypertrophy and minor valvular regurgitation. Genetic analysis confirmed a pathogenic SLC22A5 mutation. Treatment with L-carnitine supplementation, metabolic support, and seizure management led to rapid clinical and biochemical improvement. This case highlights the importance of considering PCD in infants with multisystem involvement, particularly in populations with high rates of consanguinity, and underscores the critical role of early diagnosis and intervention in improving outcomes. https://igj.tums.ac.ir/index.php/igj/article/view/240