Why does homocystinuria affect connective tissue?
Cysteine is deficient in homocystinuria, and this amino acid is necessary for proper crosslinking of structural proteins such as collagen and fibrillin in connective tissue and bone, the suspensory ligament of the eye, and the extracellular milieu of endothelial cells. On this basis, altered collagen may be responsible for the lens dislocation and osteoporosis, whereas altered proteins in the elastomeric complex or its substructure (fibrillin) may be responsible for the phenotypic similarity to Marfan syndrome. Altered endothelial function (from the cytotoxic effect of homocysteine) and increased platelet activation are responsible for the thrombosis and subsequent mental retardation.
