[Amyloidosis. II. Current pathogenetic and clinico-nosographic aspects]

Amyloidosis is due to the overproduction of a precursor protein and its conversion into products capable of polymerisation into fibrils. The primary form, or that associated with multiple myeloma or Waldenström's macroglobulinaemia, marked by the presence of protein AL, includes the overproduction of Ig light chains followed by conversion on the part of lysosome enzymes. The forms can thus be classified as immunoproliferative diseases (plasma-cell dyscrasias). Secondary amyloidosis is primarily associated with neoplasia or chronic inflammation. Its biochemical label is the AA protein. Initially, there is overproduction of protein SAA, while the formation of AA-amyloid fibrils may theoretically be attributed to a variety of factors: changes in the amount of circulating SAA, the presence of amyloidogenetic SAA, variations in the activity of SAA catabolic systems, insufficient removal of acculated fibrils. The way in which the immunocompetent system intervenes is a controversial subject. Lesser froms of amyloidosis are known in which there are local deposits of amyloid: APUD-amyloidosis, amyloidomas. In some forms, the features of systemic accumulation are maintained, but only one organ is primarily involved. They are rarely of clinical significance (e.g. senile amyloidosis). Current biochemical techniques enable a clinical and nosographic distinction to be drawn between an Ig (AL)-amyloidosis and non-Ig (AA, APUD and AS) forms.