The potential significance of sulphated glycosaminoglycans as a common constituent of all amyloids: or, perhaps amyloid is not a misnomer.

Amyloid is a generic term referring to a group of diseases in which proteinaceous tissue deposits all have in common specific stain affinities, a common appearance in polarized light, common ultrastructure fibrillary characteristics, and uniform x-ray diffraction and infrared spectral properties. Where groups of diseases have a common underlying pathogenetic process the polypeptide responsible for the protein fibril is the same regardless of the specific disease. Where diseases have a different underlying pathogenesis the polypeptide is unique for each disease. The different amyloidogenic polypeptides are clearly not related in terms of amino acid sequence or function, yet they all tend to fold in such a way as to present the same staining, structural or spectral properties. It is proposed that amyloid fibrils are not only composed of the specific amyloidogenic polypeptide but also highly sulphated glycosaminoglycans or proteoglycans which have a profound influence on the manner in which the peptides fold and interact with each other. It is this highly charged carbohydrate which may be common to all amyloids and which plays a determining role in the final appearance of the deposit. Amyloid should therefore be considered as more than simply a protein entity but, as its name originally implied, one related to carbohydrate deposition as well.