David Gillis1, Aiswarya Krishnamohan2, Barak Yaacov3, Avraham Shaag3, Jane E Jackman2, Orly Elpeleg3. 1. Department of Pediatrics, Hadassah-Hebrew University Medical Center, Ein-Kerem, Jerusalem, Israel. 2. Department of Chemistry and Biochemistry, Ohio State Biochemistry Program and Center for RNA Biology, The Ohio State University, Columbus, Ohio, USA. 3. Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
Abstract
BACKGROUND: Trm10 is a tRNA m(1)G9 methyltransferase, which in yeast modifies 12 different tRNA species, yet is considered non-essential for viability under standard growth conditions. In humans, there are three Trm10 orthologs, one mitochondrial and two presumed cytoplasmic. A nonsense mutation in one of the cytoplasmic orthologs (TRMT10A) has recently been associated with microcephaly, intellectual disability, short stature and adolescent onset diabetes. METHODS AND RESULTS: The subjects were three patients who suffered from microcephaly, intellectual disability, short stature, delayed puberty, seizures and disturbed glucose metabolism, mainly hyperinsulinaemic hypoglycaemia. A homozygous Gly206Arg (G206R) mutation in the TRMT10A gene was identified using whole exome sequencing. The mutation segregated in the family and was absent from large control cohorts. Determination of the methylation activity of the expressed wild-type (WT) and variant TRMT10A enzymes with transcripts of (32)P -tRNA(Gly) GCC as a substrate revealed a striking defect (<0.1% of WT activity) for the variant enzyme. The binding affinity of the G206R variant enzyme to tRNA, determined by fluorescence anisotropy, was similar to that of the WT enzyme. CONCLUSIONS: The completely abolished m(1)G9 methyltransferase activity of the mutant enzyme is likely due to significant defects in its ability to bind the methyl donor S-adenosyl methionine. We propose that TRMT10A deficiency accounts for abnormalities in glucose homeostasis initially manifesting both ketotic and non-ketotic hypoglycaemic events with transition to diabetes in adolescence, perhaps as a consequence of accelerated β cell apoptosis. The seizure disorder and intellectual disability are probably secondary to mutant gene expression in neuronal tissue. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
BACKGROUND:Trm10 is a tRNA m(1)G9 methyltransferase, which in yeast modifies 12 different tRNA species, yet is considered non-essential for viability under standard growth conditions. In humans, there are three Trm10 orthologs, one mitochondrial and two presumed cytoplasmic. A nonsense mutation in one of the cytoplasmic orthologs (TRMT10A) has recently been associated with microcephaly, intellectual disability, short stature and adolescent onset diabetes. METHODS AND RESULTS: The subjects were three patients who suffered from microcephaly, intellectual disability, short stature, delayed puberty, seizures and disturbed glucose metabolism, mainly hyperinsulinaemic hypoglycaemia. A homozygous Gly206Arg (G206R) mutation in the TRMT10A gene was identified using whole exome sequencing. The mutation segregated in the family and was absent from large control cohorts. Determination of the methylation activity of the expressed wild-type (WT) and variant TRMT10A enzymes with transcripts of (32)P -tRNA(Gly) GCC as a substrate revealed a striking defect (<0.1% of WT activity) for the variant enzyme. The binding affinity of the G206R variant enzyme to tRNA, determined by fluorescence anisotropy, was similar to that of the WT enzyme. CONCLUSIONS: The completely abolished m(1)G9 methyltransferase activity of the mutant enzyme is likely due to significant defects in its ability to bind the methyl donorS-adenosyl methionine. We propose that TRMT10Adeficiency accounts for abnormalities in glucose homeostasis initially manifesting both ketotic and non-ketotic hypoglycaemic events with transition to diabetes in adolescence, perhaps as a consequence of accelerated β cell apoptosis. The seizure disorder and intellectual disability are probably secondary to mutant gene expression in neuronal tissue. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
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