Studying the role of mitochondria—the specialized structures within cells responsible for energy production—in metabolic diseases has been difficult because of a lack of animal models with the necessary mitochondrial mutations to observe these tiny organelles. However, a team from the University of Tsukuba have now generated the first mouse model carrying a disease-associated mitochondrial mutation and have shown that the resulting disease is caused by faulty RNA processing. Their study is published in Nucleic Acids Research.