Abstract
L-carnitine plays an important role in the functioning of the central nervous system, and especially in the mitochondrial metabolism of fatty acids. Altered carnitine metabolism, abnormal fatty acid metabolism in patients with autism spectrum disorder (ASD) has been documented. ASD is a complex heterogeneous neurodevelopmental condition that is usually diagnosed in early childhood. Patients with ASD require careful classification as this heterogeneous clinical category may include patients with an intellectual disability or high functioning, epilepsy, language impairments, or associated Mendelian genetic conditions. L-carnitine participates in the long-chain oxidation of fatty acids in the brain, stimulates acetylcholine synthesis (donor of the acyl groups), stimulates expression of growth-associated protein-43, prevents cell apoptosis and neuron damage and stimulates neurotransmission. Determination of L-carnitine in serum/plasma and analysis of acylcarnitines in a dried blood spot may be useful in ASD diagnosis and treatment. Changes in the acylcarnitine profiles may indicate potential mitochondrial dysfunctions and abnormal fatty acid metabolism in ASD children. L-carnitine deficiency or deregulation of L-carnitine metabolism in ASD is accompanied by disturbances of other metabolic pathways, e.g., Krebs cycle, the activity of respiratory chain complexes, indicative of mitochondrial dysfunction. Supplementation of L-carnitine may be beneficial to alleviate behavioral and cognitive symptoms in ASD patients.
Highlights
Autism spectrum disorder (ASD) involves different neurodevelopment disorders with heterogeneous etiology
L-carnitine allows the transport of long-chain fatty acids from the cytosol to the mitochondrial matrix by the mitochondrial carnitine–acylcarnitine cycle, which is composed of three enzymes: carnitine palmitoyltransferase I (CPT I), carnitine-acylcarnitine translocase (CACT), and carnitine palmitoyltransferase II (CPT II) (Figure 2)
It is possible that mitochondrial defects are caused by L-carnitine deficiency and blockade of secondary fatty acid oxidation, as low serum concentrations of free and total carnitine were observed in children with ASD in comparison to the control group (p < 0.001) [116]
Summary
Autism spectrum disorder (ASD) involves different neurodevelopment disorders with heterogeneous etiology. L-carnitine is necessary to transfer long-chain fatty acids from the cytoplasm to mitochondria through the internal mitochondrial membrane for β-oxidation [7]. Disordered β-oxidation of long-chain fatty acids in the NSCs of the developing brain caused by. Deficiency and deregulation of carnitine metabolism accompanied by slight increases in lactate and serum ammonia in ASD are symptoms of mitochondrial dysfunction [11] (Figure 1). ASD children show low concentrations of free L-carnitine, as L-carnitine is connected with long-chain fatty acids in tissues and serum. Increases in the concentrations of long- and very-long-chain fatty acids, suggesting their impaired β-oxidation, were reported in the serum of ASD children [13,14].
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