Finnish type amyloidosis
Overview
Amyloidosis is a clinical disorder caused by extracellular deposition of insoluble abnormal fibrils that injure tissue. The fibrils are formed by the aggregation of misfolded, normally soluble proteins. In humans, about 23 different unrelated proteins are known to form amyloid fibrils in vivo. All types of amyloid consist of a major fibrillar protein that defines the type of amyloid (approximately 90%) plus various minor components.
Diagnosis
Amyloid can be diagnosed on microscopic examination of affected tissue. Amyloid deposits can be identified histologically by Congo red staining and viewing under polarized light where amyloid deposits produce a distinctive 'apple green birefringence'. Further, specific tests are available to more precisely identify the amyloid protein. Biopsies are taken from affected organs (for example, the kidney), or often in the case of systemic amyloid, from the rectum, gingiva, or omentum (anterior abdominal adipose tissue). In addition, all amyloid deposits contain serum amyloid P component (SAP), a circulating protein of the pentraxin family. Radionuclide SAP scans have been developed which can anatomically localize amyloid deposits in patients. Bleeding under the skin, called amyloid purpura, is seen in a minority of patients with amyloidosis.