Strong evidence of an essential role of LETM1 (Blomen et al., 2015; Wang et al., 2015) is in line with the notion of the vital function in maintaining the mitochondrial volume homeostasis, as postulated by P. Mitchell and with the finding that loss of LETM1 on one allele is sufficient to determine (or cause) the Wolf Hirschhorn syndrome (WHS). The gene discussed is LETM1; the disease is Wolf-Hirschhorn syndrome.