A Belgian ancestral haplotype harbours a highly prevalent mutation for 17q21-linked tau-negative FTLD.

Among patients with frontotemporal lobar degeneration (FTLD), the respective frequencies of dominant 17q21-linked tau-negative FTLD (with unidentified molecular defect) and 17q21-linked tau-positive FTLD (due to MAPT mutations) remain unknown. Here, in a series of 98 genealogically unrelated Belgian FTLD patients, we identified an ancestral 8 cM MAPT containing haplotype in two patients belonging to multiplex families DR2 and DR8, without demonstrable MAPT mutations, in which FTLD was conclusively linked to 17q21 [maximum summed log of the odds (LOD) score of 5.28 at D17S931]. Interestingly, the same DR2-DR8 ancestral haplotype was observed in five additional familial FTLD patients, indicative of a founder effect. In the FTLD series, the DR2-DR8 ancestral haplotype explained 7% (7 out of 98) of FTLD and 17% (7 out of 42) of familial FTLD and was seven times more frequent than MAPT mutations (1 out of 98 or 1%). Clinically, DR2-DR8 haplotype carriers presented with FTLD often characterized by language impairment, and in one carrier the neuropathological diagnosis was FTLD with rare tau-negative ubiquitin-positive inclusions. Together, these results strongly suggest that the DR2-DR8 founder haplotype at 17q21 harbours a tau-negative FTLD causing mutation that is a much more frequent cause of FTLD in Belgium than MAPT mutations.

Characterization of ubiquitinated intraneuronal inclusions in a novel Belgian frontotemporal lobar degeneration family.

The most common histologic feature in patients with frontotemporal lobar degeneration (FTLD) is intracellular brain inclusions of yet uncharacterized proteins that react with antiubiquitin (Ub) antibodies, but not with tau or synuclein (FTLD-U). We identified a four-generation Belgian FTLD family in which 8 patients had dominantly inherited FTLD. In one patient, we showed frontotemporal atrophy with filamentous Ub-positive intracellular inclusions in absence of tau pathology or any alterations in the levels of soluble tau. We characterized the cellular and subcellular localization and morphology of the inclusions. Ub-positive inclusions predominantly occurred within neurons (>97%), but were also observed within oligodendroglia (approximately 2%) and microglia (<1%), but not within astroglia. Regarding the subcellular localization, the intranuclear inclusions (INI) were up to approximately four-fold more frequent than the cytoplasmic inclusions, although the latter were more specific to neurons. The INIs frequently appeared spindle-shaped and 3-dimensional confocal reconstructions identified flattened, leaf-like structures. Ultrastructurally, straight 10- to 18-nm-diameter filaments constituted the spindle-shaped inclusions that occurred in close proximity to the nuclear membrane. Staining for HSP40, p62, and valosin/p97 was observed in only a minority of the inclusions. Whereas the precise nature of the protein remains elusive, characterization of such familial FTLD-U patients would be helpful in identifying a common denominator in the pathogenesis of familial and the more prevalent sporadic FTLD-U.

Molecular diagnostic tools in Creutzfeldt-Jakob disease and other prion disorders.

Clinical criteria and cerebrospinal fluid biomarkers for the diagnosis of human prion diseases (sporadic, iatrogenic or variant Creutzfeldt-Jakob disease and genetic inherited transmissible spongiform encephalopathies) are now widely available and show a sensitivity and specificity of approximately 98%. Final diagnosis of prion diseases is obtained by post-mortem examination upon identification of the pathological conformer of the prion protein (PrPSc) in the brain. Several diagnostic kits are now available that facilitate the immunochemical measurement of PrPSc. Several new molecular diagnostic techniques, aimed at increasing the sensitivity and specificity of PrPSc detection and at identifying markers of disease other than PrPSc, are the subject of ongoing studies. The aim of these studies is to develop preclinical screening tests for the identification of infected but still healthy individuals. These tests are also essential to investigate the safety of blood or blood-derived products and to ensure meat safety in European countries.

Extracellular protein deposition correlates with glial activation and oxidative stress in Creutzfeldt-Jakob and Alzheimer's disease.

The relation of protein deposition with glial cells and oxidative stress was studied in Creutzfeldt-Jakob disease (CJD), Alzheimer's disease (AD) and neurologically healthy control patients. Three neocortical areas, the hippocampus, and the cerebellum of 20 CJD, 10 AD and 10 control patients were immunohistochemically examined for the presence of astroglia, microglia, and protein depositions. To investigate the level of oxidative stress the percentage of neurons with cytoplasmic hydroxylated DNA was determined. Astroglia, microglia and oxidative stress were located around amyloid-beta depositions and a clear quantitative relation was identified. These markers were only increased in the hippocampus of AD compared to controls. Quantitative analysis in these groups showed a correlation between the oxidative stress level and the number of microglia in the grey matter. All markers were increased in the grey matter and the cerebellum of CJD when compared to AD and controls. The highest numbers of lesions were observed in a CJD population with a rapid disease progression. Quantitative analysis showed a correlation between the oxidative stress level and all glial cells. Further analysis showed that the number of microglia was related to the intensity of the prion depositions. Glial cells in the brain are thought to be the main producers of oxidative stress, resulting in neuronal death. Our results confirm that this close relationship exists in both AD and CJD. We also show that an increased number of glial cells and therefore possibly oxidative stress is associated with the disease progression.

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.