The brown bowel syndrome: a possible smooth muscle mitochondrial myopathy?

Two cases of lipofuscinosis of the gastrointestinal tract are described, and a mitochondrial origin of the pigment is proposed. The mechanism of formation of lipofuscin is discussed, with particular reference to the maintenance of structurally and functionally intact mitochondrial membranes. The central role of vitamin E is considered, and its biochemical significance to mitochondrial metabolism is emphasized. Comparisons are drawn between the abnormalities demonstrated within the smooth muscle cells of the two cases described, and the muscle cells observed in cases of skeletal muscle myopathies of mitochondrial origin. It is proposed that lipofuscinosis of the gastrointestinal tract, otherwise known as the 'brown bowel syndrome', may be regarded as a smooth muscle myopathy of mitochondrial origin.