CPT2 rs74315300: What Your Genotype Means
The rs74315300 variant in the CPT2 gene involves a specific change in the protein-building instructions for the CPT2 enzyme. It is primarily associated with the myopathic form of carnitine palmitoyltransferase II (CPT II) deficiency, a condition that affects how the body processes certain fats for energy.
What each genotype means
Typical CPT2 function
This genotype represents the common, non-variant sequence at this position in the CPT2 gene. Individuals with this profile do not carry the specific p.Ser113Leu pathogenic variant associated with CPT2 deficiency.
This is the most common genotype found in the general population across all ancestries.
CPT2 deficiency carrier
This genotype indicates you carry one copy of the p.Ser113Leu variant, also known as c.338C>T. While this variant is associated with the adult-onset myopathic form of CPT2 deficiency when inherited in two copies, carriers typically do not exhibit symptoms of the condition. You should discuss any concerns regarding muscle health or metabolic function with your healthcare provider.
This genotype is rare, with the variant allele occurring at a frequency of less than 0.2% globally, though it is more frequently observed in European populations.
Increased risk for CPT2 deficiency
This genotype indicates you carry two copies of the p.Ser113Leu variant. This variant is recognized as a pathogenic cause of the adult-onset myopathic form of CPT2 deficiency, which can lead to muscle pain and rhabdomyolysis, often triggered by stress, exercise, or fasting. Please consult with a medical geneticist or your primary care physician to discuss clinical implications and appropriate management.
This homozygous genotype is extremely rare in the general population.
Understanding the rs74315300 Variant
The variant rs74315300, often referred to as p.Ser113Leu or S113L, is a single nucleotide polymorphism located within the CPT2 gene. This specific genetic change results in the substitution of the amino acid serine with leucine at position 113 of the CPT2 protein. Because this change occurs in the coding region of the gene, it can alter the structure and function of the resulting enzyme. In the context of genetic research, this variant is widely recognized as the most common pathogenic allele associated with the myopathic form of CPT II deficiency. It is frequently identified in clinical testing for individuals presenting with symptoms related to muscle metabolism, as it accounts for a significant portion of the disease-causing alleles found in affected populations.
The Role of the CPT2 Gene
The CPT2 gene provides instructions for making an enzyme called carnitine palmitoyltransferase 2. This enzyme is essential for the body's ability to use long-chain fatty acids for energy. Specifically, it works within the mitochondria—the powerhouses of the cell—to help transport these fats so they can be broken down and converted into fuel. When the CPT2 enzyme is not functioning correctly, the body cannot efficiently utilize these fats, especially during periods of increased energy demand, such as prolonged exercise or fasting. This metabolic bottleneck can lead to the accumulation of fatty acids and a lack of energy for muscle tissues, which is the underlying mechanism for the symptoms observed in the myopathic form of CPT II deficiency.
Research and Clinical Associations
Research consistently links the rs74315300 variant to the myopathic form of CPT II deficiency, which is characterized by recurrent episodes of muscle pain, weakness, and myoglobinuria—a condition where muscle breakdown products are released into the urine. While often called the 'adult' form, studies have shown that symptoms can also manifest in childhood. The evidence for this association is strong, with the variant appearing in approximately 60% of pathogenic alleles in patients with this specific phenotype. However, it is important to note that the presence of this variant alone does not guarantee a specific clinical outcome. Clinical presentation can vary, and the severity of the condition often depends on whether an individual carries one or two copies of the variant, as well as the presence of other genetic factors.
Interpreting Your Genetic Information
If you have received information regarding your status for the rs74315300 variant, it is essential to understand that this is not a medical diagnosis. Genetic testing results should always be interpreted by a qualified healthcare professional or a genetic counselor who can place the findings in the context of your personal and family health history. Because this variant is associated with a metabolic condition, individuals who are concerned about potential symptoms, such as exercise-induced muscle pain or weakness, should discuss these findings with their clinician. They can provide guidance on whether further biochemical testing or clinical evaluation is necessary. Never use genetic data to make independent decisions about your health, diet, or exercise routines without professional medical oversight.
How common is this variant?
The rs74315300 variant is rare globally, with a minor allele frequency of less than 0.2% in large population databases like gnomAD, though it is more frequently observed in European populations.
Frequently asked questions
Is rs74315300 the same as S113L?
Yes, rs74315300 is the identifier for the genetic variant that results in the amino acid change known as p.Ser113Leu or S113L in the CPT2 protein.
Does having the TT genotype mean I have CPT II deficiency?
The TT genotype is strongly associated with the myopathic form of CPT II deficiency, but a diagnosis requires clinical evaluation by a doctor. You should discuss your results with a healthcare provider to understand what they mean for your specific health.
Can I prevent symptoms if I carry this variant?
Management of CPT II deficiency typically involves avoiding known triggers like prolonged fasting or intense exercise. Please consult with a metabolic specialist or your primary care physician to discuss appropriate lifestyle management.
How common is this variant?
The variant is considered rare in the general population, with an allele frequency of less than 0.2%. It is more commonly found in individuals of European ancestry.
Sources & further reading
Educational information only, last refreshed 10/26/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs74315300?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in CPT2
This variant is associated with stress-induced myopathic forms of carnitine palmitoyltransferase II deficiency.
This variant in the CPT2 gene is involved in fatty acid oxidation, which is essential for energy production during metabolic stress.
This variant is associated with stress-induced myopathic forms of Carnitine palmitoyltransferase II deficiency.