THIRD INTERNATIONAL CONFERENCE ON ALZHEIMER’S DISEASE S65

Some cases have defined mutations in the/-amyloid precursor protein (APP) gene on chromosome 21, others do not. Persons with trisomy 21 presumably get AD because they constitutively overexpress APP. Despite these differences in aetiology, all cases seem to have similar clinical and pathological features. The simplest explanation of the fact that there are several aetiologies, but a single pathology, is that a pathological cascade occurs which can be triggered in several ways. This cascade is APP mismetabolism ->fi -amyloid deposition -> tau phosphorylation/tangle formation -z- cell death. It is not clear why the disease pathology apparently spreads around neuronal pathways, but the fact that upregulation of APP can be mediated through interleukin responsive and heat shock responsive elements in its promoter suggests that @-amyloid deposition may induce upregulation of APP in neurons surrounding the initiating plaque. This upregulation could thus cause mismetabolism of APP at distant terminals of those neurons which surround the plaque.

254 CANDIDATE GENES FOR LATE-ONSET ALZHEIMER’S DISEASE, Roses, A.D., Alberta M.J., Saunders, A.M., Gilbert, JR. , Strittmatter, W.J., Schmeckel, D.E., and Pericak-Vance, M.A. Joseph and Kathleen Ekyan Alzheimer’s Disease Research Center, Duke University Medical Center, Durham, North Carolina 27710, U.S.A.

Linkage techniques are used to evaluate the genetic contribution of candidate genes. Locus heterogeneity for familial Alzheimer’s Disease (FAD) has been demonstrated by: 1) the identification of three mutations at Amyloid Precursor Protein codon 717 (APP717) in early onset FAD, 2) linkage support for a region on the long arm of CH19 in late-onset FAD, 3) a high lod score for a large early- onset FAD family that excludes APP as a locus on CH21 (FAD4 of the Hyslop et al series), and 4) several large early-onset pedigrees (including the Volga-German families of Schellenberg et al) that are unlinked to CH21 or CH19. Whether the Alzheimer’s Disease phenotype represents more than one pathogenetic mechanism (Alzheimer’s Diseases) or a similar process contributed by multiple loci is unclear. In order to evaluate the contribution of candidate genes on CH19, comparative gene mapping studies have identified several intriguing loci; including nerve growth factor alpha and gamma sub-units, epidermal growth factor binding protein, apolipoprotein E. transforming growth factor beta, octomer binding protein 2. kallekrein family genes (serine proteases), and others. A systematic approach using highly polymorphic microsatellite repeat markers located at or near the candidate genes as part of a directed effort to fine map the CH19q13.1-13.4 region is in progress. These analyses will be useful in narrowing the chromosomal region within which relevant genetic factors are located. Other traditional methodologies that use specific relevant probes, including in situ hybridization and mRNA expression studies, as well as immunopathological analyses, can then be applied. The development of highly polymorphic candidate gene related microsatellite probes will also be useful for two locus genetic model analyses that assume a joint contribution to the genetic basis for the phenotype.

255 ASSESSMENT OF APP GENE MUTATIONS IN A LARGE SET OF FAMILIAL AND SPORADIC AD PATIENTS R.Ta"zi, G.Vaula** D.Romano, M.Mortilla*, T.Huang, R.Tupler * W.Wasco, B.Hyman, J.Gusella, g.St.George-Hyslop , Dept. Neurology MGH, Boston, MA, Tanz Neuroscience. U. Toronto, Toronto, Ontario

In 1987, both a gene defect for familial Alzheimer disease (FAD) and the APP gene encoding the myloid protein precursor were mapped to chromosome 2<. Several FAD pedigrees have been show" to carrv mutations in the APP gene: Defects in APP have not appeared to be common causes of FAD evidenced by the presence of multiple obligate crossovers between APP and FAD in several FAD

pedigrees. One of these pedigrees is the Italian family FADL, a large kindred showing suggestive evidence for linkage to DNA markers on chromosome 21. Since the apparent APP crossover in FAD4 might be accounted for by a" intragenic recombination event or segregation of different mutations in different family branches, we further assessed APP as a candidate gene in this pedigree. All exo".s and exon/intron borders of the major APP transcript APP751 were sequenced in FAD4 and FADl, a second large kindred, and no mutations were observed. We also sequenced exons 16 and 17 (which encode the j3A4 peptide) in 30 (20 early and 10 late onset) additional FAD kindreds and 11 sporadic AD cases, screened 56 FAD kindreds and 81 cases of sporadic AD for the presence of the FAD-associated mutation, APP717 Val+Ile (by Bcl I digestion), and typed 25 FAD pedigrees for genetic linkage to APP. 38 FAD pedigrees were assessed for mutations in exons 16, 17, 18, 7, 5, and 4 by single stranded conformational analysis. No APP gene mutations or mutation-associated single-stranded conformational polymorphisms were found in any of the AD samples examined in this study, suggesting that the APP gene mutations are probably a rare cause of FAD.

256 HEREDITARY ALEHEIYER DISBASE WITH A GUANINE TO THYMINE MISSENSE CHABGE AT POBITIOI 1924 OF THE AMYLOID PRECURSOR PROTEIU (APP) GENE. B. Ghetti, M. R. Farlow, J. Murrell, and M. D. Benson Indiana University School of Medicine, Indianapolis, IN, USA

Seven patients from five generations of an Indiana kindred showed presenile dementia. The mean age of onset is 43 years, duration 6 years, and mean age at death 50 years. Initially, there are mild memory deficits, difficulty with orientation and inability to complete tasks at work or home. After 2 to 4 years, there are progressive memory and cognitive deficits as well as inability for self-care. We are studying neuropathologically three patients. Classic features of Alzheimer disease are observed. Neurofibrillary tangles (NFT) are numerous in the hippocampus, the frontal, temporal and insular cortices. NFT are also found in the hypothalamus and the substantia nigra, but are rarely seen in the striatum and thalamus. Most neocortical plaques are composed of neuritic processes and do not show a central amyloid core. In the hippocampus, plaques with conspicuously large amyloid cores are numerous in the end folium, the Ammon's horn and the subiculum. The plaques are immunolabeled with antibodies to a 28-residue synthetic peptide homologous to the NH2-terminal region of the amyloid &protein. While B-protein immunopositive deposits in the walls of meningeal and parenchymal vessels are only occasionally seen, prominent subpial ribbon-like deposits are detected by these antibodies. Along with a mild involvement of cerebellar parenchymal vessels prominent i.mmUnOpOsitiVe deposits are also seen in th; neuropil of the cerebellar molecular layer. Using polymerase chain reaction and direct DNA sequencing, Exon 15 (numbered by the APP 695 transcript) of the APP gene showed a mutation at position 1924 changing guanine to thymine. All six affected testable patients had this base pair change. (Supported by USPHS RoI NS29822 and by the American Health Assistance Foundation).

257 DNA SEQUENCE STUDIES OF THE APP GENE IN A FAMILY WITH FAD. M. Mortilla, G. Vaula, R. Tupler, W. Lukiw, Ii. Karlinsky, M. Percy, C. Bergeron, D. Crapper McLachlan, P. St. George-Hyslop. Depts. of Medicine, Neurology, Psychiatry, Pathology, Obstetrics 8 Gynecology, Universi ty of Toronto, Tans Neuroscience Bldg., 6 Queen's Park Crescent W., Toronto, Ontario, Canada.

Recently mutations in codon 717 of the APP gene have been reported in a few pedi