tRNA-ALA is a mitochondrial noncoding gene that produces the nucleic acid adaptor molecule transfer RNA (tRNA). tRNAs bind relevant amino acids and function during protein formation by providing the ribosome with the correct peptide sequence. tRNA-ALA specifically adds alanine during translation.
Disorders associated with tRNA-ALA deficiency include myopathy, myotonic dystrophy-like disorders, and chronic progressive external ophthalmoplegia.
tRNA-ALA is located in mitochondrial DNA and is 69 bases long ranging from 5587 to 5655 base pairs existing in the minus orientation. It is a non-coding gene that transcribes into an alanine transporting RNA molecule. It carries an alanine specific anti-codon sequence that binds specific mRNA codons during protein formation in the ribosome.
Heteroplasmic loss-of-function mutations in tRNA-ALA are causative of myotonic dystrophy-like disorders, myopathy, and chronic progressive external ophthalmoplegia. Mitochondrial genes are maternally inherited, and oocytes may contain a mixture of mitochondria with varying genotypes; therefore the clinical severity of tRNA-ALA deficiency is linked to mitochondrial heteroplasmy.
Al-Shamsi et al., 2016 performed Whole Exome Sequencing (WES) in 85 Emirati patients who were admitted to the metabolic unit with un-diagnosable inborn errors of metabolism (IEM) and other genetic disorders. Among the cohort with IEM in whom mutational pathogenicity was confirmed, 1 patient was diagnosed with Mitochondrial tRNA-ALA deficiency (MTTA). A heteroplasmic homozygous transition in the non-coding mitochondrial gene tRNA-ALA (c.5591G>A) was identified as the cause. Cases with mitochondrial DNA mutations in this study exhibited 56-59% heteroplasmy. The patient clinically presented with myopathy, ptosis, and failure to thrive; muscle biopsy revealed normal mitochondria.
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