Primary carnitine deficiency is a fatty acid oxidative metabolic disease caused by mutations in the SLC22A5 gene. Carnitine deficiency leads to the inability of long-chain fatty acids to enter the mitochondria to participate in β-oxidation, especially when the body needs fat mobilization for energy supply, and fatty acids accumulate in the cells, causing metabolic disorders and organ damage, which can clinically lead to hypoketotic hypoglycemia, dilated cardiomyopathy, lipid deposition myopathy, hepatomegaly, etc. The diagnosis relies on tandem mass spectrometry for blood free carnitine and acylcarnitine levels and gene mutation detection. L-carnitine is the main drug used to treat the disease, and most patients recover completely after treatment. Primary carnitine deficiency is due to defective carnitine transprotein function and is an autosomal recessive disorder. PCD has been reported as a common disease of fatty acid oxidative metabolism, with a prevalence in Caucasians second only to medium-chain acyl-CoA dehydrogenase deficiency. PCD is a treatable inherited metabolic disease, and early diagnosis and long-term treatment are extremely important to improve the prognosis. The progress of PCD diagnosis and treatment is reviewed as follows. In vivo, carnitine enters the cell through the transport of carnitine transporter protein on the cell membrane, which exists in the cell membrane of cardiac muscle, skeletal muscle, small intestine, renal tubules, skin fibroblasts and placenta, etc. Mutations in the gene encoding SLC22A5 cause the carnitine transporter protein to fail to colonize the cell membrane or the functional area is damaged to varying degrees, and carnitine cannot be transported into the cell, resulting in a decrease in exogenous carnitine absorbed via the intestine. This results in a decrease in exogenous carnitine absorption through the intestine and an impairment of carnitine reabsorption by the kidney, resulting in a decrease in plasma carnitine levels and a lack of carnitine in tissue cells. The main function of carnitine is to assist the transport of long-chain fatty acids into the mitochondria to participate in β-oxidation, but carnitine deficiency leads to the accumulation of long-chain fatty acids in the cytoplasm instead of entering the mitochondria. When fatty acids are required as the main source of energy, the tissues do not receive enough energy, and toxic substances such as lipids accumulate in large quantities, leading to organ damage. PCD is a potentially lethal disease that can present with chronic progressive damage to the heart, skeletal muscle, liver and other tissues, as well as acute onset and even sudden death, with wide variation in the performance of children. In addition, other factors such as infection and diet can influence the time of onset and the severity of the clinical phenotype. In recent years, with the introduction of newborn screening for this disease, some well-developed, asymptomatic patients with PCD have been identified, and six asymptomatic patients with PCD have been identified through screening in our laboratory.