<h4>Background</h4>A syndrome of young-onset diabetes mellitus associated with microcephaly, epilepsy and intellectual disability caused by mutations in the tRNA methyltransferase 10 homologue A (TRMT10A) gene has recently been described.<h4>Case report</h4>We report two siblings from the fourth family reported to have diabetes mellitus as a result of a TRMT10A mutation. This evidence concerns the gene TRMT10A and microcephaly.