In this work, we first investigated the tissue levels of Sqr mRNA and SQR protein, as well as the SQR activity, in two mouse models of primary CoQ deficiency: the Coq9R239X mouse model with fatal mitochondrial encephalopathy and the Coq9Q95X mouse model with late‐onset mild mitochondrial myopathy (Garcia‐Corzo et al, 2013; Luna‐Sanchez et al, 2015). The gene discussed is SQOR; the disease is Mitochondrial myopathy.