MTTL1 is a mitochondrial gene that encodes a transfer-RNA molecule. Specifically, this tRNA is responsible for the transfer of the amino acid leucine to its correct position during mitochondrial protein translation. It is hence designated as tRNA-Leu (UUR). The gene is also required for transcription termination of the mitochondrial genome. The mitochondrial transcription termination factor (MTERF) binds to a 13 bp termination sequence located within the MTTL1 gene.
The gene has been implicated in several mitochondrial disorders including MELAS Syndrome, Leigh Syndrome, Maternally Inherited Diabetes and Deafness (MIDD), Sudden Infant Death Syndrome (SIDS), Cyclic Vomiting Syndrome (CVS), Mitochondrial Complex IV Deficiency, Age Related Macular Degeneration 1 (ARMD1) and Myoclonic Epilepsy associated with Ragged-Red Fibers (MERRF).
MTTL1 is a 75 bp long gene located in the mitochondrial genome from position 3,230 to 3,304. Several mutations in the gene have been implicated in various disorders. However, the transition 3243A>G is the most common heteroplasmic mtDNA mutation associated with disease. It has been linked to MELAS Syndrome, MIDD, ARMD1, CVS, mitochondrial complex IV deficiency, and MERRF/MELAS overlap syndrome.
Alila et al. (2015) studied the mitochondrial genome of two Tunisian families affected by dilated cardiomyopathy. The index patient from Family A was a 9-month-old female with dilated mitochondrial cardiomyopathy, left ventricular hypertrophy and increased lactic acid levels. She carried a de novo heteroplasmic m.3243A>G mutation in the MT-TL1 gene, which creates an ApaI restriction site. The mutation was found to be present in high heteroplasmic loads (63.64%). In addition, several missense mutations such as m.10895A>G (p.46N>D, MT-ND4 gene) and m.12950A>C (p.205N>T, MT-ND5 gene) were also detected. Family B consisted of a 9-year-old female with dilated cardiomyopathy, congenital cataracts and facial dysmorphia. Mitochondrial analysis revealed a homoplasmic m.5182C>T (p.238T>M) mutation in the patient’s MT-ND2 gene. It was noted that the mitochondrial variants identified in families A and B both classify in the same haplogroup H2a2a1.
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