HCM and lactic acidosis are frequent presentations in some mitochondrial diseases related to dysfunctional mt‐tRNA maturation, such as those caused by biallelic variants in MTO1 (MIM# 614667), GTPBP3 (MIM# 608536), AARS2 (MIM# 612035) and RARS2 (MIM# 611524; Ghezzi et al., 2012; Gotz et al., 2011; Kopajtich et al., 2014; Lax et al., 2015). Here, MTO1 is linked to mitochondrial disease.