L. Nee

Dementia of the Alzheimer type Clinical and family study of 22 twin pairs

We studied 22 twin pairs in which one or both twins had dementia of the Alzheimer type (DAT). In four twins, diagnosis was confirmed by autopsy. Seven monozygotic (MZ) pairs were concordant for DAT; 10 MZ pairs were discordant. Two dizygotic (DZ) pairs were concordant for DAT, and 3 DZ pairs were discordant. The current concordance rate was 41% for MZ twins and 40% for DZ twins. The study supports the belief that, etiologically, DAT cannot be entirely accounted for by a single autosomal dominant gene. The data also suggest that in certain genetic circumstances, disease expression may be delayed in females.

Transmission and age‐at‐onset patterns in familial Alzheimer's disease Evidence for heterogeneity

We evaluated age at onset and lifetime risk for Alzheimers disease (AD) in 70 kindreds with familial AD (designated FAD) composed of 541 affected and 1,066 unaffected offspring of demented parents who were identified retrospectively. Using a survival analysis method which takes into account affected persons with unknown onset ages and unaffected persons with unknown censoring ages, we found lifetime risk of AD among at-risk offspring by age 87 to be 64%. Analysis of age at onset among kindreds showed evidence for a bimodal distribution: in this sample, families with a mean onset age of less than 58 years were designated as having early-onset, while late-onset families had a mean onset age greater than 58 years. At-risk offspring in early-onset families had an estimated lifetime risk for dementia of 53%, which is significantly less than the risk of 86% that was estimated for offspring in late-onset families. Men and women in early-onset families had equivalent risk of dementia. In late-onset families, the risk to female offspring was somewhat higher than to male offspring but this difference was marginally significant. Lifetime risk of dementia in early-onset FAD kindreds is consistent with an autosomal dominant inheritance model. Our results may suggest that late-onset FAD has at least 2 etiologies; AD in some families may be transmitted as a dominant trait, whereas a proportion of cases in these and other late-onset families may be caused by other genetic or shared environmental factors.

Familial and sporadic Alzheimer's disease Neuropathology cannot exclude a final common pathway

Whether all etiologic forms of Alzheimers disease (AD) share a final common pathway is a major issue.We determined the severity and regional distribution of neuronal loss, amyloid plaques, neuritic plaques (NPs), and neurofibrillary tangles (NFTs), and calculated the ratio of neuronal loss to NPs and NFTs in brains of 19 familial AD (FAD) patients with linkage to chromosome 14, six AD patients with mutations of chromosome 21 (codon 717 of the beta-amyloid precursor protein gene), and 11 sporadic AD (SAD) patients. There was no difference in the pattern of distribution of the various pathologic features or in the ratio of neuronal loss to NPs or NFTs in any AD group. However, FAD groups could be distinguished from SAD by the greater severity and the lack of influence of apolipoprotein E genotype on pathology. These differences may reflect differences in age at onset rather than different etiopathologic mechanisms. The similarity of pathologic findings in the different AD groups provides evidence for a final common pathophysiologic pathway in AD. NEUROLOGY 1996;46: 406-212

Frontotemporal dementia with novel tau pathology and a Glu342Val tau mutation

It is unclear how tau gene mutations cause frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP‐17), but those in exon 10 (E10) or the following intron may be pathogenic by altering E10 splicing, perturbing the normal 1:1 ratio of four versus three microtubule‐binding repeat tau (4R:3R tau ratio) and forming tau inclusions. We report on a 55‐year old woman with frontotemporal dementia and a family history of FTDP‐17 in whom we found a novel E12 (Glu342Val) tau gene mutation, prominent frontotemporal neuron loss, intracytoplasmic tau aggregates, paired helical tau filaments, increased 4R tau messenger RNA, increased 4R tau without E2 or E3 inserts, decreased 4R tau with these inserts, and a 4R:3R tau ratio greater than 1 in gray and white matter. Thus, this novel Glu342Val mutation may cause FTDP‐17 by unprecedented mechanisms that alter splicing of E2, E3, and E10 to preferentially increase 4R tau without amino terminal inserts and promote aggregation of tau filaments into cytopathic inclusions. Ann Neurol 2000;48:850–858

Familial Alzheimer's disease: Site of mutation influences clinical phenotype

Alzheimers disease (AD) is caused by multiple genetic and/or environmental etiologies. Because differences in the genetically determined pathogenesis may cause differences in the phenotype, we examined age at onset and age at death in 90 subjects with dominantly inherited AD due to different mutations (amyloid precursor protein, presenilin‐1, and presenilin‐2 genes). We found that among patients with dominantly inherited AD, genetic factors influence both age at onset and age at death. Ann Neurol 2000;48:376–379

Gilles de la Tourette syndrome: Clinical and genetic studies in a midwestern city

Clinical and genetic observations of Gilles de la Tourette syndrome were carried out on members of 14 families from the Minneapolis area. An unusual number of the families were of Jewish and other Eastern European ancestry, and in all but one of these families multiple members were affected. These observations parallel our earlier findings based on 21 families from the New York City area. Together with recent evidence indicating relative instability of a specific enzyme in some patients, these observations suggest that there is a genetically determined form of Gilles de la Tourette syndrome.

Worldwide distribution of PSEN1 Met146Leu mutation. A large variability for a founder mutation

Objective: Large kindreds segregating familial Alzheimer disease (FAD) offer the opportunity of studying clinical variability as observed for presenilin 1 (PSEN1) mutations. Two early-onset FAD (EOFAD) Calabrian families with PSEN1 Met146Leu (ATG/CTG) mutation constitute a unique population descending from a remote common ancestor. Recently, several other EOFAD families with the same mutation have been described worldwide. Methods: We searched for a common founder of the PSEN1 Met146Leu mutation in families with different geographic origins by genealogic and molecular analyses. We also investigated the phenotypic variability at onset in a group of 50 patients (mean age at onset 40.0 ± 4.8 years) by clinical, neuropsychological, and molecular methodologies. Results: EOFAD Met146Leu families from around the world resulted to be related and constitute a single kindred originating from Southern Italy before the 17th century. Phenotypic variability at onset is broad: 4 different clinical presentations may be recognized, 2 classic for AD (memory deficits and spatial and temporal disorientation), whereas the others are expressions of frontal impairment. The apathetic and dysexecutive subgroups could be related to orbital-medial prefrontal cortex and dorsolateral prefrontal cortex dysfunction. Conclusions: Genealogic and molecular findings provided evidence that the PSEN1 Met146Leu families from around the world analyzed in this study are related and represent a single kindred originating from Southern Italy. The marked phenotypic variability might reflect early involvement by the pathologic process of different cortical areas. Although the clinical phenotype is quite variable, the neuropathologic and biochemical characteristics of the lesions account for neurodegenerative processes unmistakably of Alzheimer nature.

AMY plaques in familial AD Comparison with sporadic Alzheimer’s disease

Objective: To assess AMY expression in familial AD (FAD). Background: The discovery of nonβ-amyloid (Aβ), plaque-like deposits composed of a 100-kd protein (AMY) in sporadic AD (SAD) brains prompted us to determine whether these plaques (AMY plaques) also occur in AD due to mutations of the presenilin-1 (PS-1), presenilin-2 (PS-2), or the amyloid precursor protein (APP) genes. Methods: We used immunohistochemistry and confocal laser scanning microscopy to probe the brains of 22 patients with FAD (13 with PS-1, 5 with PS-2, and 4 with APP mutations) and 14 patients with SAD. Results: AMY plaques were present in all SAD and FAD brains, including an FAD/PS-1 brain from an individual with preclinical disease. The morphology of AMY plaques in SAD and FAD brains was indistinguishable, but they differed from Aβ deposits because AMY plaques lacked an immunoreactive core. AMY plaques sometimes colocalized with Aβx-42 deposits, but they did not colocalize with Aβx-40 plaque cores in either SAD or FAD brains. The percent of cortical area occupied by AMY was greater in FAD than in SAD brains (mean percent area = 9.8% and 5.9%, t = 2.487, p = 0.018). In particular, APP and PS-1 cases had more AMY deposition than PS-2 or SAD cases (12.9%, 10.5%, 6.2% in APP, PS-1, and PS-2 AD). Conclusions: AMY plaques are consistently present in familial AD due to presenilin-1 (PS-1), PS-2, and amyloid precursor protein mutations, and they can begin to accumulate before the emergence of dementia.

A novel but non-pathogenic mutation in exon 4 of the human amyloid precursor protein (APP) gene.

Mutations in the beta-amyloid precursor protein (APP) gene have been associated with both familial Alzheimer disease (FAD) and with hereditary cerebral haemorrhage. The polymerase chain reaction was used to both amplify and sequence exon 4 of the APP gene from genomic DNA of subjects with FAD and normal control subjects. A novel, rare, conservative DNA sequence variant was discovered at nucleotide 459 of codon 153 (valine) in exon 4 of the APP gene in an affected member of a large FAD pedigree. Segregation studies indicate that this mutation is likely to be non-pathogenic, but must be recognized and discriminated from pathogenic mutations during sequencing studies of the APP gene in patients with FAD.

Molecular Genetic Strategies in Familial Alzheimer’s Disease: Theoretical and Practical Considerations

Genetic linkage studies have provided evidence to indicate that there is a defective gene on chromosome 21 which causes the autosomal dominant form of Alzheimer’s disease (AD), at least in the four large pedigrees examined. Further studies have indicated that the β-amyloid gene and the superoxide dismutase-1 gene are not the site of the familial AD (FAD) mutation, and that duplication of large regions of chromosome 21 is not the pathogenetic mechanism in either FAD or sporadic AD. Additional studies are currently under way to more precisely map the location of the FAD gene in order to expedite the ultimate goal of isolating and characterizing the actual FAD gene.