Parenchymal preamyloid and amyloid deposits in the brains of patients with hereditary cerebral hemorrhage with amyloidosis--Dutch type

Cerebral Small Vessel Disease in Sporadic and Familial Alzheimer Disease

Alzheimer disease (AD) is the most common cause of dementia. Biological definitions of AD are limited to the cerebral burden of amyloid β plaques, neurofibrillary pathology, and neurodegeneration. However, current evidence suggests that various features of small vessel disease (SVD) are part of and covertly modify both sporadic and familial AD. Neuroimaging studies suggest that white matter hyperintensities explained by vascular mechanisms occurs frequently in the AD spectrum. Recent advances have further emphasized that frontal periventricular and posterior white matter hyperintensities are associated with cerebral amyloid angiopathy in familial AD. Although whether SVD markers precede the classically recognized biomarkers of disease is debatable, post-mortem studies show that SVD pathology incorporating small cortical and subcortical infarcts, microinfarcts, microbleeds, perivascular spacing, and white matter attenuation is commonly found in sporadic as well as in mutation carriers with confirmed familial AD. Age-related cerebral vessel pathologies such as arteriolosclerosis and cerebral amyloid angiopathy modify progression or worsen risk by shifting the threshold for cognitive impairment and AD dementia. The incorporation of SVD as a biomarker is warranted in the biological definition of AD. Therapeutic interventions directly reducing the burden of brain amyloid β have had no major impact on the disease or delaying cognitive deterioration, but lowering the risk of vascular disease seems the only rational approach to tackle both early- and late-onset AD dementia.

Processing of Mutant β-Amyloid Precursor Protein and the Clinicopathological Features of Familial Alzheimer's Disease

Alzheimer's disease (AD) is a complex, multifactorial disease involving many pathological mechanisms. Nonetheless, single pathogenic mutations in amyloid precursor protein (APP) or presenilin 1 or 2 can cause AD with almost all of the clinical and neuropathological features, and therefore, we believe an important mechanism of pathogenesis in AD could be revealed from examining pathogenic APP missense mutations. A comprehensive review of the literature, including clinical, neuropathological, cellular and animal model data, was conducted through PubMed and the databases of Alzforum mutations, HGMD, UniProt, and AD&FTDMDB. Pearson correlation analysis combining the clinical and neuropathological data and aspects of mutant APP processing in cellular models was performed. We find that an increase in Aβ42 has a significant positive correlation with the appearance of neurofibrillary tangles (NFTs) and tends to cause an earlier age of AD onset, while an increase in Aβ40 significantly increases the age at death. The increase in the α-carboxyl terminal fragment (CTF) has a significantly negative correlation with the age of AD onset, and β-CTF has a similar effect without statistical significance. Animal models show that intracellular Aβ is critical for memory defects. Based on these results and the fact that amyloid plaque burden correlates much less well with cognitive impairment than do NFT counts, we propose a "snowball hypothesis": the accumulation of intraneuronal NFTs caused by extracellular Aβ42 and the increase in intraneuronal APP proteolytic products (CTFs and Aβs) could cause cellular organelle stress that leads to neurodegeneration in AD, which then resembles the formation of abnormal protein "snowballs" both inside and outside of neurons.

Retinal changes in the Tg-SwDI mouse model of Alzheimer's disease

Alzheimer's disease (AD), a debilitating neurodegenerative illness, is characterized by neuronal cell loss, mental deficits, and abnormalities in several neurotransmitter and protein systems. AD is also associated with visual disturbances, but their causes remain unidentified. We hypothesize that the visual disturbances stem from retinal changes, particularly changes in the retinal cholinergic system, and that the etiology in the retina parallels the etiology in the rest of the brain. To test our hypothesis, quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were employed to assess changes in acetylcholine receptor (AChR) gene expression, number of retinal cells, and astrocytic gliosis in the Transgenic Swedish, Dutch and Iowa (Tg-SwDI) mouse model as compared to age-matched wild-type (WT). We observed that Tg-SwDI mice showed an initial upregulation of AChR gene expression early on (young adults and middle-aged adults), but a downregulation later on (old adults). Furthermore, transgenic animals displayed significant cell loss in the photoreceptor layer and inner retina of the young adult animals, as well as specific cholinergic cell loss, and increased astrocytic gliosis in the middle-aged adult and old adult groups. Our results suggest that the changes observed in AD cerebrum are also present in the retina and may be, at least in part, responsible for the visual deficits associated with the disease.

Deficient cerebral clearance of vasculotropic mutant Dutch/Iowa Double A beta in human A betaPP transgenic mice

Cerebral amyloid angiopathy (CAA) is a prominent pathological feature of Alzheimer's disease and related familial CAA disorders. However, the mechanisms that account for the cerebral vascular accumulation of amyloid beta-peptide (A beta) have not been defined. Recently, we reported novel transgenic mice (Tg-SwDI) expressing neuronally derived Swedish/Dutch/Iowa vasculotropic mutant human A beta precursor (A betaPP) that develop early-onset and robust accumulation of fibrillar cerebral microvascular A beta. Deficient clearance of Dutch/Iowa mutant A beta from brain across the capillary blood-brain barrier into the circulation may contribute to its potent cerebral accumulation. To further evaluate this theory, we generated a new transgenic mouse (Tg-Sw) that is nearly identical to Tg-SwDI, except lacking the Dutch/Iowa A beta mutations. Tg-Sw and Tg-SwDI mice expressed comparable levels of human A betaPP in brain and not in peripheral tissues. However, Tg-SwDI mice strongly accumulated Dutch/Iowa mutant A beta in brain, particularly in the cerebral microvasculature, whereas Tg-Sw mice exhibited no accumulations of wild-type A beta. Conversely, Tg-SwDI mice had no detectable Dutch/Iowa mutant A beta in plasma whereas Tg-Sw mice exhibited consistent levels of human wild-type A beta in plasma. Together, these findings suggest that while wild-type A beta is readily transported out of brain into plasma, Dutch/Iowa mutant A beta is deficient in this clearance process, likely contributing to its robust accumulation in the cerebral vasculature.

The protective role of vitamin E in vascular amyloid beta-mediated damage

Amyloid beta peptide (Abeta) accumulation produces the senile plaques in the brain parenchyma characteristic of Alzheimer's Disease (AD) and the vascular deposits of Cerebral Amyloid Angiopathy (CAA). Oxidative stress is directly involved in Abeta-mediated cytotoxicity and antioxidants have been reported as cytoprotective in AD and CAA. Vitamin E has antioxidant and hydrophobic properties that render this molecule as the main antioxidant present in biological membranes, preventing lipid peroxidation, carbonyl formation and inducing intracellular modulation of cell signalling pathways. Accordingly, vascular damage produced by Abeta and prooxidant agents can be decreased or prevented by vitamin E. The protective effect of vitamin E against Abeta cytotoxicity in vascular cells in comparison to the neuronal system is reviewed in this chapter.

Dense-core senile plaques in the Flemish variant of Alzheimer's disease are vasocentric

Alzheimer's disease (AD) is characterized by deposition of beta-amyloid (Abeta) in diffuse and senile plaques, and variably in vessels. Mutations in the Abeta-encoding region of the amyloid precursor protein (APP) gene are frequently associated with very severe forms of vascular Abeta deposition, sometimes also accompanied by AD pathology. We earlier described a Flemish APP (A692G) mutation causing a form of early-onset AD with a prominent cerebral amyloid angiopathy and unusually large senile plaque cores. The pathogenic basis of Flemish AD is unknown. By image and mass spectrometric Abeta analyses, we demonstrated that in contrast to other familial AD cases with predominant brain Abeta42, Flemish AD patients predominantly deposit Abeta40. On serial histological section analysis we further showed that the neuritic senile plaques in APP692 brains were centered on vessels. Of a total of 2400 senile plaque cores studied from various brain regions from three patients, 68% enclosed a vessel, whereas the remainder were associated with vascular walls. These observations were confirmed by electron microscopy coupled with examination of serial semi-thin plastic sections, as well as three-dimensional observations by confocal microscopy. Diffuse plaques did not associate with vessels, or with neuritic or inflammatory pathology. Together with earlier in vitro data on APP692, our analyses suggest that the altered biological properties of the Flemish APP and Abeta facilitate progressive Abeta deposition in vascular walls that in addition to causing strokes, initiates formation of dense-core senile plaques in the Flemish variant of AD.

Biology of A beta amyloid in Alzheimer's disease

The genetic associations with the pathological features of AD are diverse: A rapidly growing number of mutations in presenilin 1 and 2 on chromosomes 14 and 1, respectively, are found in many early-onset FAD patients (Lendon et al., 1997). In addition, beta PP mutations are found in a small percentage of early-onset FAD kindreds. The apoE4 allele on chromosome 19 is associated with the presence of the most common form of AD, sporadic AD (Wisniewski & Frangione, 1992; Namba et al., 1991). However, it is clear that other proteins are also involved in the pathogenesis of AD, since some early-onset FAD kindreds do not have linkage to PS1, PS2, apoE, or beta PP, while at least 50% of late-onset AD is unrelated to apoE. Other proteins which have been implicated in the formation of senile plaques, but so far are not known to have any genetic linkage to AD, include proteoglycans (Snow et al., 1987), apoA1 (Wisniewski et al., 1995a), alpha 1-antichymotrypsin (Abraham et al., 1988), HB-GAM (Wisniewski et al., 1996a), complement components (McGeer & Rogers, 1992), acetylcholinesterase (Friede, 1965), and NAC (Ueda et al., 1993). Which of these proteins will be the most important for the etiology of the most common form of AD, late-onset sporadic AD, remains an open question. Three of the genes which are now known to be linked to AD, including PS1, beta PP, and apoE, have been established immunohistochemically and biochemically to be components of senile plaques (see Fig. 1). This raises at least two possibilities: either each of these proteins is part of one pathway with A beta-related amyloid formation as a final causative pathogenic event or amyloid deposition in AD is a reactive process related to dysfunction of a number of different CNS proteins. Whether or not amyloid formation is directly causative in the pathogenesis of AD, current data suggest that new therapeutic approaches which may inhibit the aggregation and/or the conformational change of sA beta to A beta fibrils (Soto et al., 1996) have the greatest likelihood to make a significant impact on controlling amyloid accumulation in AD.

Animal models of cerebral beta-amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a significant risk factor for hemorrhagic stroke in the elderly, and occurs as a sporadic disorder, as a frequent component of Alzheimer's disease, and in several rare, hereditary conditions. The most common type of amyloid found in the vasculature of the brain is beta-amyloid (A beta), the same peptide that occurs in senile plaques. A paucity of animal models has hindered the experimental analysis of CAA. Several transgenic mouse models of cerebral beta-amyloidosis have now been reported, but only one appears to develop significant cerebrovascular amyloid. However, well-characterized models of naturally occurring CAA, particularly aged dogs and non-human primates, have contributed unique insights into the biology of vascular amyloid in recent years. Some non-human primate species have a predilection for developing CAA; the squirrel monkey (Saimiri sciureus), for example, is particularly likely to manifest beta-amyloid deposition in the cerebral blood vessels with age, whereas the rhesus monkey (Macaca mulatta) develops more abundant parenchymal amyloid. These animals have been used to test in vivo beta-amyloid labeling strategies with monoclonal antibodies and radiolabeled A beta. Species-differences in the predominant site of A beta deposition also can be exploited to evaluate factors that direct amyloid selectively to a particular tissue compartment of the brain. For example, the cysteine protease inhibitor, cystatin C, in squirrel monkeys has an amino acid substitution that is similar to the mutant substitution found in some humans with a hereditary form of cystatin C amyloid angiopathy, possibly explaining the predisposition of squirrel monkeys to CAA. The existing animal models have shown considerable utility in deciphering the pathobiology of CAA, and in testing strategies that could be used to diagnose and treat this disorder in humans.

The "nonamyloidogenic" p3 fragment (amyloid beta17-42) is a major constituent of Down's syndrome cerebellar preamyloid

Down's syndrome (DS) patients show accelerated Alzheimer's disease (AD) neuropathology, which consists of preamyloid lesions followed by the development of neuritic plaques and neurofibrillary tangles. The major constituents of preamyloid and neuritic plaques are amyloid beta (Abeta) peptides. Preamyloid lesions are defined as being Abeta immunoreactive lesions, which unlike neuritic plaque amyloid are Congo red-negative and largely nonfibrillar ultrastructurally. DS patients can develop extensive preamyloid deposits in the cerebellum, without neuritic plaques; hence, DS cerebellums are a source of relatively pure preamyloid. We biochemically characterized the composition of DS preamyloid and compared it to amyloid in the neuritic plaques and leptomeninges in the same patients. We found that Abeta17-42 or p3 is a major Abeta peptide of DS cerebellar preamyloid. This 26-residue peptide is also present in low quantities in neuritic plaques. We suggest that preamyloid can now be defined biochemically as lesions in which a major Abeta peptide is p3.

Hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D): II--A review of histopathological aspects

Cerebral amyloid-beta (A beta) angiopathy is the histopathological hallmark of hereditary cerebral hemorrhage with amyloidosis (Dutch) (HCHWA-D). A beta deposits are found mainly in the cerebral and cerebellar meningocortical blood vessels and as plaques throughout the cerebrocortical gray matter. A beta deposition in arteries and arterioles starts at the junction of media and adventitia and proceeds to involve the media causing degeneration of the vascular smooth muscle cells. Cerebrocortical arterioles often show one or two layers of radial A beta around a layer of homogenous A beta that replaces the media. Degenerating neurites, reactive astrocytes and microglial cells may surround cerebrocortical angiopathic arterioles and capillaries, probably in reaction to invasion of the perivascular neuropil by A beta fibrils. Furthermore, clusters of coarse extracellular matrix deposits may be found near A beta-laden cerebrocortical arterioles. The amyloid-associated proteins, cystatin C, and beta PP colocalize diffusely with Dutch vascular A beta, whereas HLA-DR immunoreactivity is found only in the periphery of the diseased vessel wall. The latter phenomenon may be related to the presence of perivascular cells. Angiopathic blood vessels frequently show structural changes. The relation of the described pathology to the development of hemorrhage, infarction and leukoencephalopathy needs further elucidation.

A beta A4 amyloid precursor protein gene and Alzheimer's disease

Alzheimer's disease is a senile dementia caused by progressive neurodegeneration of the central nervous system. One of the most prominent pathological characteristics is beta A4 amyloid deposition in senile plaques in the brain parenchyma and in cerebral blood vessels. beta A4 amyloid is processed from a larger integral membrane protein, the beta A4 amyloid precursor protein. Different pathogenic mutations in this protein have been detected in a small number of Alzheimer's disease families. Here functional implications of these mutations on the processing of the precursor protein and the beta A4 amyloid deposition will be discussed with respect to the pathogenesis of Alzheimer's disease and related disorders.

Co-localization of beta/A4 and cystatin C in cortical blood vessels in Dutch, but not in Icelandic hereditary cerebral hemorrhage with amyloidosis

Based on the recent discovery of co-localization of beta/A4 and cystatin C in cortical blood vessels of patients with cerebral hemorrhages due to sporadic amyloid angiopathy and patients with Alzheimer's disease we investigated the presence of these two proteins in the cortical blood vessels of patients suffering from hereditary cerebral hemorrhage with amyloidosis of the Dutch (n = 11) and the Icelandic (n = 2) type. The brains of three patients with sporadic cerebral amyloid angiopathy were also investigated. Blood vessels of the Dutch patients clearly showed immunostaining with beta/A4 as well as with cystatin C antibodies, whereas the blood vessels of Icelandic patients showed only staining with cystatin C. In one of the three sporadic amyloid angiopathy patients co-localization was shown as well. The co-localization of mutated beta/A4 with normal cystatin C in the Dutch patients suggests that cystatin C deposition occurs secondarily to beta/A4 deposition. This is probably also the case in sporadic amyloid angiopathy and Alzheimer's disease. Cystatin C deposition may play a role in the development of cerebral hemorrhages and leukoencephalopathy.

Alzheimer's disease and soluble A beta

The discovery of soluble amyloid beta (sA beta) suggests that the role of amyloid in Alzheimer's disease (AD) is similar to the previously studied systemic amyloidoses and alters the notion that membrane damage is the initial event in AD. The disease state is characterized by the abnormal accumulation of a normal degradative peptide, which becomes resistant to further proteolysis due to a conformational change. Mutations in the beta PP gene have been found in a very small percentage of AD cases; hence other factors, both genetic and environmental, need to be identified. Priority needs to be given to detailed studies of the structural differences between sA beta and the A beta in amyloid deposits. This will help uncover the determining factors governing the aggregation of sA beta. These structural alterations may be critical for the possible toxic effects A beta and/or associated proteins (molecular chaperones, e.g., apolipoprotein E) have on brain cell function.

Ubiquitinated neurites are associated with preamyloid and cerebral amyloid beta deposits in patients with hereditary cerebral hemorrhage with amyloidosis Dutch type

Hereditary cerebral hemorrhage with amyloidosis Dutch type (HCHWA-D) is characterized clinically by recurrent strokes and pathologically by deposition of amyloid beta (A beta) in cerebral vessel walls and, to a lesser extent, in the neuropil. Distinct from Alzheimer's disease, amyloid formation in HCHWA-D is not associated with neurofibrillary changes. Since a central issue in the pathophysiology of Alzheimer's disease and related conditions is the role of A beta in the neurodegenerative process, we investigated HCHWA-D brains for the presence of neuritic abnormalities using antibodies to ubiquitin and to phosphorylated neurofilaments. The study showed that amyloid deposits in the vessel walls and in the neuropil were surrounded by abnormal ubiquitinated neurites, suggesting that A beta deposition induces neuritic changes.

Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type share a decrease in cerebrospinal fluid levels of amyloid beta-protein precursor

The amyloid beta-protein is a 39-42 amino acid peptide that is deposited in senile plaques and in cerebral vessel walls in individuals with Alzheimer's disease, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D), and, to a much lesser extent, normal aging. It is derived from abnormal proteolytic processing of its parent protein, the amyloid beta-protein precursor. Here we show that individuals with the HCHWA-D mutation and clinically manifesting the disease have markedly decreased cerebrospinal fluid levels of soluble amyloid beta-protein precursor (0.7 +/- 0.4 micrograms/ml) compared with age-matched normal subjects (3.0 +/- 0.2 micrograms/ml) as determined by quantitative immunoblotting and enzyme-linked immunosorbent assays. Similarly, age-matched patients diagnosed with probable Alzheimer's disease also have decreased cerebrospinal fluid levels of soluble amyloid beta-protein precursor (1.0 +/- 0.3 micrograms/ml). These parallel findings suggest a common biochemical marker for these two diseases and further establish the pathogenic relatedness of HCHWA-D and Alzheimer's disease.

Acute phase proteins but not activated microglial cells are present in parenchymal beta/A4 deposits in the brains of patients with hereditary cerebral hemorrhage with amyloidosis-Dutch type

With immunohistochemical staining methods on cryostat sections we investigated the brains of three patients with hereditary cerebral hemorrhage with amyloidosis-Dutch type, one of the cerebral beta/A4 amyloid diseases. Immunostaining for beta/A4 protein revealed numerous non-fibrillar beta/A4 depositions (amorphous or diffuse plaques) in the brain parenchyma in addition to extensive vascular amyloid deposition. All amorphous plaques contain complement proteins and alpha 1-antichymotrypsin but activated microglial cells expressing major histocompatibility (MHC) class II antigens HLA-DR and leucocyte adhesion molecules belonging to the lymphocyte-function-associated antigen (LFA)-1 family are virtually absent in cortical gray matter. Our findings are discussed from the view that a cascade of events including acute phase proteins and activated microglial cells are involved in classical amyloid plaque formation.

Presenile dementia and cerebral haemorrhage linked to a mutation at codon 692 of the beta-amyloid precursor protein gene

Several families with an early-onset form of familial Alzheimer's disease have been found to harbour mutations at a specific codon (717) of the gene for the beta-amyloid precursor protein (APP) on chromosome 21. We now report, a novel base mutation in the same exon of the APP gene which co-segregates in one family with presenile dementia and cerebral haemorrhage due to cerebral amyloid angiopathy. The mutation results in the substitution of alanine into glycine at codon 692. These results suggest that the clinically distinct entities, presenile dementia and cerebral amyloid angiopathy, can be caused by the same mutation in the APP gene.

Molecular biology of Alzheimer's amyloid--Dutch variant

Hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D) (or familial cerebral amyloid angiopathy) and familial Alzheimer's disease (FAD) share several properties. Both are autosomal dominant forms of cerebral amyloidosis characterized by beta-amyloid (A beta) deposition. In HCHWA-D the A beta is predominantly found in blood vessels and in early parenchymal plaques, whereas in AD parenchymal A beta deposits in the form of senile plaques and neurofibrillary tangles are a more prominent finding. Point mutations in the amyloid precursor protein (APP) have recently been described, in both conditions. A G to C transversion at codon 618 (extracellular portion of APP695), producing a single amino acid substitution of glutamine instead of glutamine acid, occurs in HCHWA-D; whereas mutations at codon 642 in the intramembrane region of APP695 (phenylalanine, isoleucine, or glycine instead of valine) are associated with early onset FAD. This suggests that the site of particular mutations in the APP gene and the type of amino acid substitution in the APP holoprotein are more important in determining clinicopathological phenotype and age at which A beta is deposited. Thus FAD and HCHWA-D can be regarded as two sides of the same coin.

Comparison between the Icelandic and Dutch forms of hereditary cerebral amyloid angiopathy

Hereditary cerebral amyloid angiopathy has been described in Icelandic and Dutch families. Although the clinical manifestations show similarities, biochemical characterization revealed that amyloid in the Icelandic patients consists of cystatin C and in the Dutch patients of beta-protein. Both diseases are caused by a single base mutation leading to the same amino acid (viz. glutamine). Furthermore, both cystatin C and the beta-protein precursor are protease inhibitors. Therefore, the mechanism of amyloidogenesis may be similar in both diseases. A comparison of clinical, pathological, genetic, and biochemical aspects of these two types of hereditary cerebral amyloid angiopathy is presented.

Hereditary cerebral hemorrhage with amyloidosis--Dutch type: a congophilic angiopathy. An overview

Hereditary cerebral hemorrhage with amyloidosis--Dutch type (HCHWA-D) is characterized by recurrent cerebral hemorrhages and dementia at a relatively young age. The symptoms are caused by extensive deposition of amyloid in cerebral arterioles and leptomeningeal arteries. A point-mutation in the beta-protein precursor gene on chromosome 21 is the underlying cause of the disease. This paper summarizes the clinical, radiologic, pathologic, and genetic features of this disease, with special attention to the relation between HCHWA-D and Alzheimer's disease, which is also characterized by beta-protein deposition.

Codon 618 variant of Alzheimer amyloid gene associated with inherited cerebral hemorrhage

Hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D) is an autosomal dominant form of severe cerebrovascular amyloid angiopathy causing recurrent strokes during the fifth and sixth decades of life. The major constituent of the amyloid deposits in HCHWA-D is the amyloid beta-protein (A beta), also found in Alzheimer's disease. A point mutation in the DNA sequence encoding A beta has been found in 2 unrelated patients with HCHWA-D, and an assay detecting the single base change was developed for diagnostic purposes. We describe the detection of the point mutation in a patient living in the United States, suffering from recurring cerebral hemorrhages, who only recently was diagnosed with HCHWA-D. In addition, we tested a number of family members, and found the mutation in 2 additional individuals, one of them too young to exhibit clinical manifestations. This study combined with the study of two other families in Holland indicates that the codon 618 variant in the amyloid precursor protein gene segregates with HCHWA-D.

Inherited amyloids of the nervous system

A diverse group of biochemically distinct proteins give rise to amyloids, each of which is associated with a different disease. These amyloid proteins share numerous properties and typically arise from the abnormal processing of an amyloid precursor protein. The classification, mechanisms and biochemistry of amyloid fibril formation are reviewed here, and two inherited types of amyloid affecting the nervous system are described.

Hereditary cerebral hemorrhage with amyloidosis--Dutch type: its importance for Alzheimer research

Alzheimer's disease is now commonly regarded as a form of 'amyloid encephalopathy'. Amyloid deposits in the cerebral blood vessels and parenchyma consist mainly of a unique protein called amyloid beta protein (A beta P), which has a molecular weight of 4 kDa and is 42 amino acids long. These deposits are thought to be of pathogenetic importance in Alzheimer's disease. Recently, therefore, attention has been focused on the process of turnover of the precursor of A beta P to amyloid fibrils, and the deposition and persistence of A beta P in this disease. The study of several other diseases with cerebral A beta P deposition can be informative in this respect, because they allow the comparison of different pathogenetic mechanisms that lead to this type of deposition. One of these diseases is hereditary cerebral hemorrhage with amyloidosis- Dutch type (HCHWA-D), which is the subject of this review.