Lipopigments in veterinary pathology: pathogenesis and terminology.

The lipopigments are a heterogenous group of pigments whose pathogenesis and terminology is confused. Whereas there is epidemiological and observational evidence that ceroid is derived from degeneration and peroxidation of unsaturated lipid, the assumption that all so-called lipopigments are similarly formed, is questioned. In particular, recent studies have distanced the pathogenesis of the pigment found in the ceroid-lipofuscinoses from that perceived for ceroid. The importance of protein rather than lipid in the pathogenesis of the pigment of ceroid-lipofuscinosis and of age pigment from the equine thyroid is noted. In the former the essential feature is storage of the DCCD binding protein subunit c of mitochondrial ATP synthase. There is a need for more analytical studies on isolated pigments which are generally more soluble than anticipated by the literature. It is proposed that the term ceroid be limited to a family of pathological pigments where lipid degeneration and peroxidation is implied from observational and/or epidemiological factors. The term age pigment is unequivocal and preferred for age related pigment not obviously complicated by other factors. The terms lipofuscin and lipopigment retain a usefulness as generic terms, particularly where the nature of the pigment is uncertain. The term ceroid-lipofuscinosis for the inherited storage diseases of children and animals is misleading. The term "proteolipid proteinosis" has been suggested to define this group of diseases but this is perhaps premature until their full pathogenesis is known.