MT-TH

The MT-TH gene provides instructions for making a particular type of RNA, a molecule that is a chemical cousin of DNA. This type of RNA, called transfer RNA (tRNA), helps assemble protein building blocks known as amino acids into full-length, functioning proteins. The MT-TH gene provides instructions for a specific form of transfer RNA that is designated as tRNA^His. This molecule attaches to a particular amino acid, histidine (His), and inserts it into the appropriate locations in many different proteins.

The tRNA^His molecule is present only in cellular structures called mitochondria. These structures convert energy from food into a form that cells can use. Through a process called oxidative phosphorylation, mitochondria use oxygen and simple sugars to create adenosine triphosphate (ATP), the cell's main energy source. The tRNA^His molecule is involved in the assembly of proteins that carry out oxidative phosphorylation.

mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes - caused by mutations in the MT-TH gene

A small number of people with the features of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) have been identified with a mutation in the MT-TH gene. These individuals also have some features of another mitochondrial disorder, myoclonic epilepsy and ragged red fibers (MERRF). The signs and symptoms of this MELAS/MERRF overlap syndrome appear in early adulthood. They include recurrent severe headaches, muscle weakness or difficulty with muscle coordination (ataxia), hearing loss, stroke-like episodes including a loss of consciousness, seizures, and other problems affecting the nervous system.

In the few described cases, a particular mutation in the MT-TH gene appears to be responsible for the overlapping features of MELAS and MERRF. This mutation changes a single DNA building block (nucleotide) in the gene. Specifically, it replaces the nucleotide guanine with the nucleotide adenine at gene position 12147 (written as G12147A). Researchers have not determined how this genetic change alters energy production in mitochondria or causes the varied signs and symptoms of the MELAS/MERRF overlap syndrome.

other disorders - associated with the MT-TH gene

Another mutation in the MT-TH gene may increase the risk of developing a heart condition called cardiomyopathy. People with cardiomyopathy have a weakened heart muscle that is unable to pump blood effectively. A particular change in the MT-TH gene has been identified in several adults with cardiomyopathy, but without other common signs of mitochondrial disease such as neurological abnormalities. This mutation replaces the nucleotide guanine with the nucleotide adenine at gene position 12192 (written as G12192A). It is unclear why this alteration in mitochondrial DNA may increase a person's risk of developing heart problems without affecting other parts of the body.