An atypical intronic deletion widens the spectrum of mutations in hereditary spastic paraplegia.

OBJECTIVE: To identify the genetic mutation responsible for autosomal dominant spastic paraplegia (HSP) in a large family with a "pure" form of the disorder. BACKGROUND: The disease locus in most families with HSP is genetically linked to the SPG4 locus on chromosome 2p21-p22. Some of these families have mutations in the splice-site or coding regions of the spastin gene (SPAST). METHODS: Linkage and mutational analyses were used to identify the location and the nature of the genetic defect causing the disorder in a large family. After the disease phenotype was linked to the SPG4 locus, all 17 coding regions and flanking intronic sequences of SPAST were analyzed by single-strand conformation polymorphism analysis (SSCP) and compared between affected and normal individuals. Direct sequencing and subcloning methods were used to investigate incongruous mobility shifts. RESULTS: The genomic sequence of SPAST showed a heterozygous four--base pair deletion (delTAAT) near the 3' splice-site of exon three in all 11 affected individuals but not in 21 normal family members or in 50 unrelated controls (100 chromosomes). CONCLUSIONS: This study identifies an atypical intronic microdeletion in SPAST that causes HSP and widens the spectrum of genetic abnormalities that cause the disorder.

Distinguishable effects of presenilin-1 and APP717 mutations on amyloid plaque deposition.

Both APP and PS-1 are causal genes for early-onset familial Alzheimer's disease (AD) and their mutation effects on cerebral Abeta deposition in the senile plaques were examined in human brains of 29 familial AD (23 PS-1, 6 APP) cases and 14 sporadic AD cases in terms of Abeta40 and Abeta42. Abeta isoform data were evaluated using repeated measures analysis of variance which adjusted for within-subject measurement variation and confounding effects of individual APP and PS-1 mutations, age at onset, duration of illness and APOE genotype. We observed that mutations in both APP and PS-1 were associated with a significant increase of Abeta42 in plaques as been documented previously. In comparison to sporadic AD cases, both APP717 and PS-1 mutation cases had an increased density (measured as the number of plaques/mm(2)) and area (%) of Abeta42 plaques. However, we found an unexpected differential effect of PS-1 but not APP717 mutation cases. At least some of PS-1 but not APP717 mutation cases had the significant increase of density and area of Abeta40-plaques as compared to sporadic AD independently of APOE genotype. Our results suggest that PS-1 mutations affect cerebral accumulation of Abeta burden in a different fashion from APP717 mutations in their familial AD brains.

Inherited Alzheimer's disease PS-1 olfactory function: a 10-year follow-up study.

This study was undertaken to evaluate smell tests as a clinical marker for identifying mutation carrier status and determining the clinical diagnosis of presenilin-1 Alzheimer's disease (AD) in family members of those afflicted with the disease. Ten years ago, we gave the self-administered, 40-question scratch and sniff University of Pennsylvania Smell Identification Test to 18 at-risk family members, individuals with dominantly-inherited Alzheimer's disease. Testing results were normal 10 years ago except in the case of one individual who had smoked three packs of cigarettes a day for more than 23 years. Four subjects tested in 1990 are now afflicted with Alzheimer's disease, including the smoker. The smell test in 1990 did not demonstrate predictive capabilities before clinical conversion to dementia. At follow-up, two subjects were too impaired to take the test. Two "converted" from normal smell function to abnormal function with a wide range in score. Study findings indicate that the smell test is too variable a measure to be used as a reliable test for predicting or verifying a diagnosis of presenilin-1 Alzheimer's disease.

Platelet APP isoform ratios in asymptomatic young adults expressing an AD-related presenilin-1 mutation.

The Alzheimer's disease (AD) related amyloid precursor protein (APP) is stored, cleaved and released similarly from neurons and from platelets. We have reported that the proportion of 120-130 to 110 kDa carboxyl-cleaved APP present in the platelets of AD patients is significantly lower than that of platelets of age-matched controls. This reduced APP isoform ratio, not seen in several other disease groups, is further reduced as the severity of AD increases. Since the neuropathology of AD is believed to begin many years before the onset of cognitive loss, we have also compared platelet APP ratios of four pre-symptomatic young adults carrying a presenilin-1 mutation to seven siblings homozygous for the normal PS-1 gene in an effort to determine whether reduced APP ratios are present before apparent cognitive loss in familial AD. Decreased platelet APP ratios were not seen in any of these subjects at this time. We will continue to monitor these subjects as they near the mean age of AD onset in these families. As the magnitude of the APP ratio reduction is proportional to the severity of cognitive loss in sporadic AD, these cognitively normal incipient AD subjects would not be expected to present significant reductions in this AD severity index at this time. Alternatively, the absence of platelet APP ratio reductions may result from a failure of platelets from familial PS-1 AD subjects to manifest altered APPs, as has been reported for PS-2 AD subjects, unlike those of sporadic AD patients. Continued monitoring of cognitive status in our sub-set of controls with AD-like low APP ratios may yet validate the ability of this assay to detect incipient sporadic AD.

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.

Familial Alzheimer's disease: site of mutation influences clinical phenotype.

Alzheimer's 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.

AMY plaques in familial AD: comparison with sporadic Alzheimer's disease.

OBJECTIVE: To assess AMY expression in familial AD (FAD). BACKGROUND: The discovery of nonbeta-amyloid (Abeta), 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 Abeta deposits because AMY plaques lacked an immunoreactive core. AMY plaques sometimes colocalized with Abeta(x-42) deposits, but they did not colocalize with Abeta(x-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.

Presenilin 1 suppresses the function of c-Jun homodimers via interaction with QM/Jif-1.

Presenilin 1 (PS1) is the causative gene for an autosomal dominant familial Alzheimer's disease (AD) mapped to chromosome 14. Here we show that QM/Jun-interacting factor (Jif)-1, a negative regulator of c-Jun, is a candidate to mediate the function of PS1 in the cell. We screened for proteins that bind to PS1 from a human embryonic brain cDNA library using the two-hybrid method and isolated one clone encoding the QM/Jif-1 gene. The binding of QM/Jif-1 to full-length PS1 was confirmed in vitro by pull-down assay, and in vivo by immunoprecipitation assays with human samples, including AD brains. Immunoelectronmicroscopic analysis showed that QM/Jif-1 and PS1 are colocalized at the endoplasmic reticulum, and the nuclear matrix in human brain neurons. Chloramphenicol acetyltransferase assays in F9 cells showed that PS1 suppresses transactivation by c-Jun/c-Jun but not by c-Jun/c-Fos heterodimers, consistent with the reported function of QM/Jif-1. By monitoring fluorescent recombinant protein and by gel mobility shift assays, PS1 was shown to accelerate the translocation of QM from the cytoplasm to the nucleus and to thereby suppress the binding of c-Jun homodimer to 12-O-tetradecanoylphorbol-13- acetate (TPA)-responsive element (TRE). PS1 suppressed c-jun-associated apoptosis by retinoic acid in F9 embryonic carcinoma cells, whereas this suppression of apoptosis is attenuated by mutation in PS1. Collectively, the novel function of PS1 via QM/Jif-1 influences c-jun-mediated transcription and apoptosis.

A lack of the R406W tau mutation in progressive supranuclear palsy and corticobasal degeneration.

Linkage disequilibrium studies suggest that progressive supranuclear palsy (PSP) is an autosomal recessive condition that maps to a polymorphism in the tau gene. These results provide evidence that homozygous mutations in the tau gene may cause PSP. Recently, a missense mutation in exon 13 of one tau allele (R406W) was found in a single family with an atypical clinicopathologic form of dominantly inherited PSP. The authors report that the R406W mutation is lacking in 25 unrelated individuals with PSP and in six unrelated individuals with another tauopathy-corticobasal degeneration.

Alzheimer's disease in 22 twin pairs--13-year follow-up: hormonal, infectious and traumatic factors.

We obtained follow-up data on 22 sets of twins where at least one twin had Alzheimer's disease (AD). The concordance rate for monozygotic twins (n = 17 pairs) was 59%, whereas that for dizygotic twins was 40%. In our series 8 monozygotic twins had hysterectomies; all had AD. The twins with hysterectomies also had a tendency to develop AD at an earlier age than their co-twin. Five twins with serious systemic infection developed AD, and they tended to have earlier onset than their corresponding twin. We found no strong evidence that head injury predisposed to AD.

Lewy bodies contain altered alpha-synuclein in brains of many familial Alzheimer's disease patients with mutations in presenilin and amyloid precursor protein genes.

Missense mutations in the alpha-synuclein gene cause familial Parkinson's disease (PD), and alpha-synuclein is a major component of Lewy bodies (LBs) in sporadic PD, dementia with LBs (DLB), and the LB variant of Alzheimer's disease (AD). To determine whether alpha-synuclein is a component of LBs in familial AD (FAD) patients with known mutations in presenilin (n = 65) or amyloid precursor protein (n = 9) genes, studies were conducted with antibodies to alpha-, beta-, and gamma-synuclein. LBs were detected with alpha- but not beta- or gamma-synuclein antibodies in 22% of FAD brains, and alpha-synuclein-positive LBs were most numerous in amygdala where some LBs co-localized with tau-positive neurofibrillary tangles. As 12 (63%) of 19 FAD amygdala samples contained alpha-synuclein-positive LBs, these inclusions may be more common in FAD brains than previously reported. Furthermore, alpha-synuclein antibodies decorated LB filaments by immunoelectron microscopy, and Western blots revealed that the solubility of alpha-synuclein was reduced compared with control brains. The presence of alpha-synuclein-positive LBs was not associated with any specific FAD mutation. These studies suggest that insoluble alpha-synuclein aggregates into filaments that form LBs in many FAD patients, and we speculate that these inclusions may compromise the function and/or viability of affected neurons in the FAD brain.

Amyloid-beta-protein isoforms in brain of subjects with PS1-linked, beta APP-linked and sporadic Alzheimer disease.

To determine whether similar abnormalities of various soluble full-length and N-terminal truncated Abeta peptides occur in postmortem cerebral cortex of affected PS1 mutation carriers, we examined the amounts of two amyloid species ending at residue 40 or at residues 42(43) using sandwich ELISA systems. Our results indicate that PS1 mutations effect a dramatic accumulation in brain of the highly insoluble potentially neurotoxic long-tailed isoforms of the Abeta peptide such as Abeta1-42(43) and Abetax-42(43). This enhancing effect of PS1 mutation on Abetax-42(43) deposition was highly similar to that of a betaAPP mutation (Val717Ile) but the effects on Abetax-40 production were significantly different between these two causal genes. In contrast to previous studies of soluble Abeta in plasma and in supernatants from cultured fibroblasts of subjects with PS1 mutations, our studies also show that there is an increase in insoluble Abetax-40 peptides in brain of subjects with PS1 mutations.

Progressive supranuclear gaze palsy is in linkage disequilibrium with the tau and not the alpha-synuclein gene.

We studied two candidate genes, tau (tau) and alpha-synuclein (SNCA), for evidence of linkage disequilibrium on a group of unrelated individuals with progressive supranuclear palsy (PSP) and a group of age-matched control subjects. The tau alpha1 allele and the tau alpha1alpha1 genotype were overrepresented in individuals with PSP and the tau polymorphism was in linkage disequilibrium with the PSP disease locus when a recessive inheritance model was employed. We also report a lack of evidence to support linkage disequilibrium between PSP and the SNCA candidate Parkinson's disease gene on chromosome 4q21-q23.

A gene (ETM) for essential tremor maps to chromosome 2p22-p25.

We report the results of linkage analysis in a large American family of Czech descent with dominantly inherited "pure" essential tremor (ET) and genetic anticipation. Genetic loci on chromosome 2p22-p25 establish linkage to this region with a maximum LOD score (Zmax) = 5.92 for the locus, D2S272. Obligate recombinant events place the ETM gene in a 15-cM candidate interval between the genetic loci D2S168 and D2S224. Repeat expansion detection analysis suggests that expanded CAG trinucleotide sequences are associated with ET. These findings will facilitate the search for an ETM gene and may further our understanding of the human motor system.

An autosomal recessive disorder with posterior column ataxia and retinitis pigmentosa.

We report an autosomal recessive form of ataxia that is not allelic to Friedreich's disease in six individuals from a large kindred with family origins traced to a common founder of German-Swiss descent. The disorder begins during early childhood with a concentric contraction of the visual fields and proprioceptive loss. Eventually blindness, a severe sensory ataxia, achalasia, scoliosis, and inanition develop by third decade. Inversion recovery MRIs of the spinal cord in affected individuals demonstrate a hyperintense signal in the posterior columns. Finding the gene responsible for this disorder may aid in our understanding of the mechanisms that cause sensory neuronal degeneration.

Proteolytic processing of presenilin-1 (PS-1) is not associated with Alzheimer's disease with or without PS-1 mutations.

Cerebral presenilin-1 protein (PS-1) is normally composed of the amino-terminal fragment (NTF) with Mr 28 kDa and the carboxy-terminal fragment (CTF) with 18 kDa. We analyzed human PS-1 in brains with early-onset familial Alzheimer's disease (FAD) with and without PS-1 mutations to study whether mutated PS-1 was abnormally metabolized. Cerebral PS-1 were found to be cleaved into two fragments of NTF and CTF independently of the occurrence of PS-1 mutation in human brains. A small portion of PS-1 was recently found to suffer another processing by caspase-3, an apoptosis-related cysteine protease. In contrast to the recent finding that the Volga-German mutation on presenilin-2 (PS-2) affects the increasing caspase-3 PS-2 fragment, the PS-1 mutation did not cause a significant change in PS-1 fragmentation. We conclude that PS-1 fragmentation and other (probably caspase-3-mediated) digestion following apoptosis occur independently of PS-1 mutations.

Evidence for a new spinocerebellar ataxia locus.

The autosomal dominant ataxias (ADA) are a diverse group of multisystem, neurodegenerative disorders characterized by mutations at several chromosomal loci (SCA types 1-5, SCA type 7, DRPLA). We excluded all the known SCA loci by mutational and linkage analyses is an American family of British origin with ADA and document that an additional ataxia locus must exist. The clinical characteristics and ethnic origin of our family are similar to the British Drew family of Walworth with the SCA type 3 mutation and differ from other families without a known ataxia locus. Individuals in our family and the Drew family initially show signs of ataxia but may develop variable degrees of ophthalmoplegia, Parkinsonian features and central demyelination. The phenotypic diversity in families without a known ataxia locus suggests that there may be several other undefined ataxia loci.

Brain MRI, lumbar CSF monoamine concentrations, and clinical descriptors of patients with spinocerebellar ataxia mutations.

OBJECTIVES: To serially assess changes in lumbar CSF biogenic amines, radiographic characteristics, and neurological signs in 34 patients with dominantly inherited ataxia. METHODS: Mutational analysis was used to identify genetic subgroups. Annual assessment of lumbar CSF monoamine metabolites using a gas chromatographic/mass spectrometric method and morphometric measurements of the cerebellum, pons, and the cervical spinal cord on MRI were analysed for each patient and compared with normal controls. RESULTS: Patients with CAG trinucleotide repeat expansions on chromosome 6p (mutSCA1) and chromosome 14q (mutSCA3) had only about one half the normal concentrations of lumbar CSF homovanillic acid (HVA) whereas, 5-hydroxyindoleacetic acid (5-HIAA) concentrations were similar to those in age matched normal subjects. The HVA and 5-HIAA concentrations in clinically similar patients without mutSCA1 or mutSCA3 were normal. One year after the first study, HVA concentrations were reduced by a mean of 22% regardless of the patient's SCA mutation. Abnormalities on MRI were consistent with a spinopontine atrophy in patients with mutSCA3, spinopontocerebellar atrophy in patients with mutSCA1, and "pure" cerebellar atrophy in patients without these mutations. CONCLUSIONS: Quantitative MRI measurements were not useful in monitoring progression of disease but lumbar CSF HVA concentrations and total scores on a revised version of the ataxia clinical rating scale seemed to progress in parallel.