Familial cerebral amyloid angiopathies and dementia.

Amyloidosis is a disorder of protein conformation leading to aggregation. The term defines a diverse group of proteins normally present in body fluids as soluble precursors that can be deposited as insoluble amyloid fibrils in different tissues producing organ dysfunction and cell death. These fibrils are composed of self-assembled, low molecular weight mass peptides adopting beta-pleated sheet structure, the conformation responsible for their physicochemical properties and tinctoreal characteristics. So far, 20 different proteins have been identified as subunits of amyloid fibrils (Westermark et al., 1999). Collectively, they are products of normal genes; however, several amyloid precursors contain abnormal amino acid substitutions that can impose an unusual potential for self-aggregation. The molecular mass of the amyloid peptides is within the 4 to 30-kDa range, with heterogeneity at the amino- and carboxyl-terminal portions found in most amyloid proteins. Increased levels of amyloid precursors, either in the circulation or locally in sites of deposition, are usually the result of overexpression or defective clearance, or both. Of the 20 amyloid proteins identified, few of them are known to cause amyloid deposition in the central nervous system, which in turn results in cognitive deficits, dementia, stroke, cerebellar and extrapyramidal signs, or a combination of them.