Carnitine palmitoyltransferase I (CPT I) deficiency is a condition that prevents the body from using certain fats for energy.

The signs and symptoms of CPT I deficiency are often brought on by episodes of increased energy demands in the body such as illness or periods of fasting. During these times, affected individuals usually develop low levels of glucose in the blood and a low level of ketones, which are normally produced when fats are broken down to be used for energy. Together, these signs are called hypoketotic hypoglycemia. This may cause individuals to experience confusion, seizures, or a lack of energy (lethargy).

People with CPT I deficiency can also develop an enlarged liver (hepatomegaly) that is not able to remove toxins from the blood efficiently. These toxins build up and can affect brain function (hepatic encephalopathy). As long as no brain damage occurs during these episodes of hepatic encephalopathy, individuals with CPT I deficiency often have normal development.

Health can decline quickly in people with CPT I deficiency. Affected individuals are encouraged to avoid prolonged fasting to prevent serious health problems. Individuals with CPT I deficiency are at risk for nervous system damage, liver failure, coma, and sudden death. These problems can begin any time between infancy to adulthood, though some individuals experience no health problems at all.

CPT I deficiency is often detected shortly after birth by newborn screening, which identifies abnormal levels of certain compounds in the blood. People with CPT I deficiency have high levels of a compound called carnitine. Cells use carnitine, a natural substance that is acquired mostly through the diet, to process fats and produce energy.

CPT I deficiency is a rare disorder, though its prevalence varies worldwide. It is estimated to occur in 1 in 750,000 to 2,000,000 infants in the United States. CPT I deficiency is more common in certain populations, including some Native Alaskan populations and some Native Pacific Island populations. In certain regions of China, CPT I deficiency is estimated to have an incidence of 1 in 102,388 infants.

Variants (also caused mutations) in the CPT1A gene cause CPT I deficiency. This gene provides instructions for making an enzyme called carnitine palmitoyltransferase 1A, which is found in the liver.

Carnitine palmitoyltransferase 1A is essential for fatty acid oxidation, which is the multistep process that breaks down (metabolizes) fats and converts them into energy. During periods of fasting, fats are an important energy source for the liver and other tissues. Within liver cells, fatty acid oxidation takes place within mitochondria, which are the energy-producing centers. Before entering mitochondria, a group of fats called long-chain fatty acids must first be attached to carnitine. Carnitine palmitoyltransferase 1A connects carnitine to long-chain fatty acids so they can enter mitochondria and be metabolized to produce energy. 

Variants in the CPT1A gene severely reduce or eliminate the activity of carnitine palmitoyltransferase 1A. As a result, there are not enough enzymes available to attach carnitine to long-chain fatty acids when energy demands are high. Without carnitine, these fatty acids cannot enter mitochondria to be broken down and used for energy. Reduced energy production can lead to some of the features of CPT I deficiency, such as hypoketotic hypoglycemia. Fatty acids and related compounds may also build up in cells and damage the liver, heart, and brain. This abnormal buildup causes the other signs and symptoms of CPT I deficiency.

Conditions that disrupt the metabolism of fatty acids, including CPT I deficiency, are known as fatty acid oxidation disorders.

Genetic Testing Information

• Genetic Testing Registry: Carnitine palmitoyl transferase 1A deficiency

Genetic and Rare Diseases Information Center

• Carnitine palmitoyl transferase 1A deficiency

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• CARNITINE PALMITOYLTRANSFERASE I DEFICIENCY

Scientific Articles on PubMed

• PubMed

• Balci MC, Karaca M, Selamioglu A, Korbeyli HK, Durmus A, Ak B, Kozanoglu T, Gokcay GF. A different perspective into clinical symptoms in CPT I deficiency. Mol Genet Metab Rep. 2023 Nov 30;38:101032. doi: 10.1016/j.ymgmr.2023.101032. eCollection 2024 Mar. Citation on PubMed
• Bennett MJ, Boriack RL, Narayan S, Rutledge SL, Raff ML. Novel mutations in CPT 1A define molecular heterogeneity of hepatic carnitine palmitoyltransferase I deficiency. Mol Genet Metab. 2004 May;82(1):59-63. doi: 10.1016/j.ymgme.2004.02.004. Citation on PubMed
• Gobin S, Thuillier L, Jogl G, Faye A, Tong L, Chi M, Bonnefont JP, Girard J, Prip-Buus C. Functional and structural basis of carnitine palmitoyltransferase 1A deficiency. J Biol Chem. 2003 Dec 12;278(50):50428-34. doi: 10.1074/jbc.M310130200. Epub 2003 Sep 29. Citation on PubMed
• Lee K, Pritchard A, Ahmad A. Carnitine Palmitoyltransferase 1A Deficiency. 2005 Jul 27 [updated 2025 Feb 20]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from http://www.ncbi.nlm.nih.gov/books/NBK1527/ Citation on PubMed
• Longo N, Amat di San Filippo C, Pasquali M. Disorders of carnitine transport and the carnitine cycle. Am J Med Genet C Semin Med Genet. 2006 May 15;142C(2):77-85. doi: 10.1002/ajmg.c.30087. Citation on PubMed or Free article on PubMed Central
• Olpin SE, Allen J, Bonham JR, Clark S, Clayton PT, Calvin J, Downing M, Ives K, Jones S, Manning NJ, Pollitt RJ, Standing SJ, Tanner MS. Features of carnitine palmitoyltransferase type I deficiency. J Inherit Metab Dis. 2001 Feb;24(1):35-42. doi: 10.1023/a:1005694320063. Citation on PubMed
• Vockley J. Long-chain fatty acid oxidation disorders and current management strategies. Am J Manag Care. 2020 Aug;26(7 Suppl):S147-S154. doi: 10.37765/ajmc.2020.88480. Citation on PubMed