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MT-TL1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

MT-TL1 gene

The MT-TL1 gene provides instructions for a transfer RNA molecule essential for the assembly of proteins that drive mitochondrial energy production.

Normal Function

The MT-TL1 gene provides instructions for making a transfer RNA (tRNA) molecule designated as tRNALeu(UUR). During protein assembly, this molecule attaches to the amino acid leucine (Leu) and inserts it into the appropriate locations in the growing protein. This process occurs within mitochondria, which use oxidative phosphorylation to create adenosine triphosphate (ATP), the cell's main energy source. In pancreatic beta cells, mitochondria also help trigger the release of insulin to regulate blood glucose levels.

Health Conditions Related to Genetic Changes

Maternally inherited diabetes and deafness

The A3243G mutation in the MT-TL1 gene is the most common cause of maternally inherited diabetes and deafness (MIDD), accounting for 85 percent of cases. This mutation reduces the ability of tRNALeu(UUR) to add leucine to proteins, impairing mitochondrial function and insulin release.

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

The A3243G mutation is also responsible for about 80 percent of cases of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). This condition is characterized by recurrent severe headaches, muscle weakness (myopathy), hearing loss, stroke-like episodes, and seizures.

Myoclonic epilepsy with ragged-red fibers

Mutations in the MT-TL1 gene have been found in individuals with MERRF/MELAS overlap syndrome, which combines features of myoclonic epilepsy with ragged-red fibers (MERRF) and MELAS, such as muscle twitches (myoclonus), ataxia, and diabetes.

Progressive external ophthalmoplegia

Mutations in the MT-TL1 gene, including A3243G, can cause progressive external ophthalmoplegia, a disorder that weakens eye muscles and causes drooping eyelids (ptosis).

Other disorders

Approximately 20 mutations in the MT-TL1 gene are associated with various symptoms, including muscle weakness, pain, extreme fatigue (exercise intolerance), and cardiomyopathy. Some children with these mutations have experienced delayed development, psychiatric problems, or autism spectrum disorder. MT-TL1 mutations have also been identified in a small number of cases of sudden infant death syndrome (SIDS).

Other Names for This Gene

  • MTTL1
  • tRNA leucine 1 (UUA/G)

Frequently Asked Questions

Women with MT-TL1 mutations can have children, but there are risks to consider. The mutation is passed to all offspring, and the severity of the disease in children can be unpredictable. Additionally, pregnancy can be physically demanding and may exacerbate symptoms in the mother, such as fatigue or hearing loss. Preconception counseling with a geneticist and a mitochondrial specialist is essential to discuss the risks of transmission and to plan for appropriate monitoring during pregnancy.
The A3243G mutation is the most common cause of maternally inherited diabetes and deafness (MIDD) and a leading cause of MELAS syndrome. Because it is maternally inherited, an affected mother will pass the mutation to all her children, but only her daughters will pass it to the next generation. The severity of symptoms varies widely among family members; some may only experience mild diabetes and hearing loss, while others may develop severe neurological issues like stroke-like episodes or seizures due to the variable expression of mitochondrial DNA.
While both conditions stem from the A3243G mutation, MIDD is primarily characterized by diabetes and progressive hearing loss, often without severe neurological involvement. MELAS, however, includes additional features such as recurrent stroke-like episodes, severe headaches, muscle weakness, and lactic acidosis. The distinction is made through clinical evaluation, blood tests for lactate levels, and brain imaging to look for stroke-like lesions, which are absent in pure MIDD.
Patients are often advised to avoid extreme physical exertion and prolonged fasting, as these can deplete mitochondrial energy reserves and trigger symptoms like lactic acidosis or stroke-like episodes. A diet rich in complex carbohydrates and regular, moderate exercise is generally recommended to maintain stable blood glucose and energy levels. Some patients may benefit from mitochondrial cocktails containing coenzyme Q10, L-carnitine, and B vitamins, though this should be discussed with a specialist.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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