In contrast, in Down syndrome fibroblasts (which contain markedly elevated mitochondrial 3-MST), the 3-MST inhibitor enhanced mitochondrial respiration and various parameters of basal and stimulated mitochondrial oxygen consumption, consistent with the classic hypothesis [5,16] that the mitochondria of Down syndrome cells are under a tonic H2S-mediated suppression of mitochondrial function. The gene discussed is MPST; the disease is Down syndrome.