Genetic evidence for a novel familial Alzheimer's disease locus on chromosome 14.

Familial Alzheimer's disease (FAD) has been shown to be genetically heterogeneous, with a very small proportion of early onset pedigrees being associated with mutations in the amyloid precursor protein (APP) gene on chromosome 21, and some late onset pedigrees showing associations with markers on chromosome 19. We now provide evidence for a major early onset FAD locus on the long arm of chromosome 14 near the markers D14S43 and D14S53 (multipoint lod score z = 23.4) and suggest that the inheritance of FAD may be more complex than had initially been suspected.

Nuclear compartmentalization of aluminum in Alzheimer's disease (AD).

Senile dementia of the Alzheimer type (AD) is a fatal encephalopathy of uncertain etiology. Whether the neurotoxin aluminum plays any role in the AD process in unknown. Here we report an increased amount of aluminum in a chromatin subcompartment, the micrococcal nuclease (MN; EC 3.1.31.1) accessible dinucleosome fraction, in neocortical nuclei isolated from 17 control and 21 AD-affected brains. At these MN-accessible loci we also observe an increase in H1 zero linker histone proteins, DNA-binding proteins which are thought to act as regulators of chromatin compaction. These data support the hypothesis that one deleterious effect of aluminum upon nuclear structure in AD-afflicted brain may be to condense brain chromatin nonrandomly through an interaction with H1 zero linker protein and thereby alter the ability of brain DNA to be effectively transcribed.

Family with 22-derived marker chromosome and late-onset dementia of the Alzheimer type: I. Application of a new model for estimation of the risk of disease associated with the marker.

We have identified 2 sisters with probable dementia of the Alzheimer type who have an unusual 22-derived marker chromosome with a greatly elongated short arm containing 2 well-separated nucleolus organizer regions. A marker chromosome similar in appearance is uncommon in the general population. Eleven of 24 of their biological relatives were also found to have the marker. The known pedigree of this family encompasses 6 generations in 2 of which there is evidence of 10 cases of dementia of the Alzheimer type. The average age-at-onset of dementia is 65.8 +/- 5.5 years; the average age-at-death among those apparently affected is 74.9 +/- 8.3 years. A new model for the estimation of risk was applied to the family data. Persons in this family with the marker were found to be 4 times more likely to develop dementia than those without the marker, the 95% confidence interval for this risk being 1-50. The probability that the association of dementia and the marker is due to chance alone is .05 (1 in 20).

Autoimmune thyroiditis associated with mild "subclinical" hypothyroidism in adults with Down syndrome: a comparison of patients with and without manifestations of Alzheimer disease.

Serum tests of thyroid function were compared in Down syndrome (DS) patients with and without manifestations of Alzheimer disease (AD). Relative to control individuals, DS patients had, overall, lower mean total T4 (P = 0.070) and T3f (P = 0.015), higher T3U (P = 0.013) and TSH (P = 0.020), no difference in free T4, and higher thyroid antithyroglobulin (ATA) (P = 0.033) and antimicrosomal autoantibody (AMA) titres (P = 0.0097). Similar trends were apparent in DS males and females, and in DS patients off all drugs. In an analysis of case/control pairs with corrections for age and sex, DS patients with AD manifestations (n = 9) had significantly lower T3 (P = 0.029) and higher AMA (P = 0.043) than paired control individuals, whereas DS patients without AD manifestations (n = 20) had significantly lower T3 (P = 0.013) but higher ATA (P = 0.0065). T3 was significantly lower in the DS patients with AD manifestations than in the unaffected (P = 0.0013). These data suggest that autoimmune thyroiditis associated with a mild "subclinical" form of hypothyroidism is common in adult DS patients and more pronounced in patients with AD manifestations than in those without. This "subclinical" hypothyroidism may contribute to cognitive deficits in ageing DS patients.

Chromatin structure and gene expression in Alzheimer's disease.

Light micrococcal nuclease digestion was used to examine DNA associated with nucleosome populations isolated from Alzheimer's disease (AD) affected superior temporal lobe neocortical nuclei. 46.1% of the immediate 5' upstream DNA sequence of the single copy neurofilament light chain (NF-L) gene was found to be associated with a mononucleosome fraction in control neocortices. This fraction was reduced to 7.4% in age-matched AD-affected neocortex. No differences in accessibility to the nuclease probe was found between AD-affected and control temporal grey matter nuclei for the human prion HuPrP gene or for the NF-L gene in nuclei isolated from the primary visual cortex or the cerebellum. An AvaI restriction endonuclease site, located 124 base pairs upstream from the TATAA box in the NF-L leader sequence, was also found to be occluded in AD-affected nuclei. From this and previous data we conclude that within the AD-affected nucleus, focused changes in neuronal chromatin conformation occur. Increases in the packing density of chromatin may reduce transcription and alter the ability of neurons to generate sufficient levels of gene products to maintain normal neocortical function.

Clinical expression of Alzheimer's disease in Down's syndrome.

Reports of the clinical manifestations of dementia in persons with Down's syndrome have been conflicting. Neuropathologic studies have been inconsistent with the clinical picture in many cases. Clarification of these issues requires longitudinal studies of patients combined with postmortem studies of brain tissue.

The molecular mechanisms of scrapie encephalopathy and relevance to human neurodegenerative disease.

We have investigated alterations in the structure and function of nuclei isolated from normal and pathological brains in a number of neurodegenerative diseases including scrapie and Alzheimer's disease. Here we summarize both general and specific changes in chromatin structure, gene expression, and neuropathological features for each encephalopathy and compare them in terms of their molecular biological similarities and differences. While both scrapie and Alzheimer's disease share a number of common alterations in genomic organization and gene activity during the pathogenic process, each neurological disease appears to operate on fundamentally different mechanisms.

Visual processing deficits as assessed by spatial frequency contrast sensitivity and backward masking in normal ageing and Alzheimer's disease.

Visual functions of patients with senile dementia of the Alzheimer type were compared with those of young people and age-matched controls. Visual acuity and spatial frequency contrast sensitivity did not differ significantly between Alzheimer patients and normal elderly subjects, although both were impaired in comparison with young subjects. Alzheimer patients required more time than ageing controls to identify letters and were susceptible to the interfering effects of a backward pattern mask on letter recognition over a longer interval. The spatial extent over which the pattern mask was effective, as well as the time interval over which a homogeneous mask interfered with letter recognition, were equivalent in normal old people and Alzheimer patients. In all the masking tasks, young people performed better than the old. It is suggested that Alzheimer's disease affects later central visual functions more than early relatively peripheral ones.

Total and poly(A) RNA yields during an aluminum encephalopathy in rabbit brains.

The yields of total and poly(A) RNA were examined in rabbit forebrains during an experimentally induced aluminum encephalopathy. Rabbits (35 day old) were injected intracranially with 13 mumole Al lactate and sacrificed 1, 3, 7, 10, or 12 days later. IRNA yields (total RNA minus transfer RNA) were not significantly altered during the encephalopathy. Poly(A) RNA yields, assayed by oligo(dT)-cellulose fractionation and by a [3H]poly(U) hybridization assay on IRNA, were increased significantly by the end of the asymptomatic stage of the encephalopathy (7 days post-Al injection). The increase in messenger RNA population may represent either a compensatory response to cell damage induced by aluminum or the accumulation of messenger RNA for proteins directly related to the expression of aluminum toxicity.

Characterization of messenger RNA from the cerebral cortex of control and Alzheimer-afflicted brain.

A detailed comparative study of RNA transcripts isolated from the neocortex of control and Alzheimer postmortem brains was made to determine whether morphological changes in the chromatin of Alzheimer neurons and glia, which we reported earlier, are accompanied by changes in the products of transcription. A number of parameters were determined including the yields of total and mRNA per gram of tissue, the relative proportions of polyadenylated [poly(A)+] mRNA in the total RNA, the size distribution of the transcripts and the length of their poly(A) tails, and the nature of their in vitro translation products. The levels of endogenous RNase activity were also measured. The effect of the agonal process on the transcript complement was examined by Northern blotting of a cloned human heat-shock cDNA to total human brain RNA. Our results reveal that the yields of total RNA, unadenylated mRNA, and poly(A) tail lengths from Alzheimer neocortex samples do not differ significantly from those of control and non-Alzheimer dementia neocortex. On the other hand we find a significant reduction in the levels and proportion of poly(A)+ mRNA in the Alzheimer samples as compared to control brain samples. Quantitative rather than qualitative differences were observed in the in vitro translation products when programmed with control and Alzheimer mRNA. No differences were found in the levels of RNase activity between control and Alzheimer samples. Heat-shock mRNA transcripts were detected in brain samples from patients in whom fever was associated with death. The direct correlation of reduced poly(A)+ mRNA and chromatin condensation in Alzheimer neocortex suggests a cause-and-effect relationship. Whether all transcribed genes are affected or only a specific subset has yet to be determined.

Aluminum, altered transcription, and the pathogenesis of Alzheimer's disease.

The etiology of some, if not all, cases of Alzheimer's disease is linked to a mutation in the proximal portion of the long arm of chromosome 21∶21q11.2 → 21q22.2. While the functional consequences of the mutation are unknown, we speculate that one consequence of the mutation is loss of the natural barriers and intracellular ligands for aluminum. As a result, aluminum gains access to several brain sites including the nuclear compartment in certain neurons of the central nervous system.Both sporadic and familial Alzheimer's disease are associated with an increased compaction of DNA within chromatin as measured by physical shearing and resistance to digestion by micrococcal nuclease and DNase I. There is also an increase in linker histone Hl(o) content on dinucleosomes released by light (3-5% ASN) micrococcal nuclease digestion, and an increase in the affinity of histone Hl(o) for DNA as measured by a salt elution technique. The change in enzyme accessibility to chromatin also involves the 5' promoter region of at least one physiologically important gene: the gene which codes for the low molecular weight moiety of neurofilament (NF-L). The conformation change involving the 5' regulator region probably reduces transcription because the pool size of the mRNA coding for NF-L is reduced to 14% of age matched control in cerebral grey matter. Reduced transcription may account for many disorders in cellular metabolic processes including the regulation of phosphorylation, calcium homeostasis, free radical metabolism, proteolysis and neurotransmitter metabolism.The experimental evidence indicates that one important toxic action of aluminum in Alzheimer's disease neocortex is to increase the binding of histones, particularly Hl(o), to DNA which results in increased compaction of chromatin and reduced transcription. The supporting evidence includes: (1) A statistically reliable correlation between the aluminum to DNA ratio on intermediate euchromatin and the amount of highly condensed heterochromatin found in a given preparation from Alzheimer affected neocortex (Crapperet al., 1980). (2) A nine-fold increase in aluminum content in Alzheimer's disease in the di- and tri- nucleosome fraction released by light micrococcal nuclease digestion of nuclei from cerebral grey matter compared to age matched controls. Compared to age matched control dinucleosomes, the Alzheimer affected dinucleosomes contain an increased abundance of the linker histone Hl(o) and an increased proportion of DNA containing the promoter region of the gene coding for NF-L. (3) A reduction in abundance to 14% of control mRNA coding for NF-L in Alzheimer affected neocortex (Crapper McLachlanet al., 1988). (4) In vitro evidence that Alzheimer linker histones bind more tightly to DNA than control and that aluminum added to nuclei,in vitro, extracted from normal control brain, enhances DNA-protein binding of Hl and Hl(o) at concentrations found in the Alzheimer affected chromatin (Lukiwet al., 1987). (5) Application of a band retardation assay indicates that aluminum,in vitro, selectively binds human Hl(o) to a 300 bp human ALU DNA fragment from a crude extract of 5% per chloric acid soluble proteins. (6) Aluminum experimentally applied to rabbit CNS induces a marked reduction in NF-L mRNA in anterior horn cells (Mumaet al., 1988). We therefore conclude that aluminum plays a major role in the pathogenesis of Alzheimer's disease. Further understanding of the role of aluminum in Alzheimer's disease requires a detailed investigation of the precise sites of co-ordination of this trivalent metal within chromatin.

BC200 RNA in normal human neocortex, non-Alzheimer dementia (NAD), and senile dementia of the Alzheimer type (AD).

BC200 RNA is a polyadenylated 200 nucleotide primate brain-specific transcript with 80% homology to the left monomer of the human Alu family of repetitive elements. Whether this transcription product contributes anything to normal brain gene function or is a residue of post transcriptional processing of brain heterogeneous nuclear RNA (hnRNA) is uncertain. However, the high abundance, tissue-specific expression and nucleotide sequence characteristics of BC200 RNA suggests that the generation of this small RNA is associated with some brain cell function. Sustained levels of the BC200 RNA transcript may be indicative of a genetically competent and normally functioning cerebral neocortex. In this investigation, we have measured the abundance of the BC200 RNA transcript in total RNA isolated from 18 temporal neocortices (Brodman area 22) of brains with no pathology and those affected with neurodegenerative disease. Neocortices were examined from 3 neurologically normal brains, 5 non-Alzheimer demented [NAD; 3 Huntington's chorea (HC), 1 amyotrophic lateral sclerosis (ALS) and 1 dementia unclassified] and 10 Alzheimer disease (AD) affected brains. Our results indicate a strong BC200 presence in both the normal brains and NAD affected neocortices, but a 70 per cent reduction in BC200 signal strength in AD afflicted brains. These results may be related to the observation that Alzheimer brains exhibit marked deficits in the abundance of neuron-specific DNA transcripts; these deficits are consistent with the idea that AD is characterized by an impairment in the primary generation of brain gene transcription products.

Calcium metabolism in aluminum encephalopathy.

Electrophysiologic deficits occurred in the in vitro hippocampal slice preparation removed from rabbits at various stages of an aluminum-induced encephalopathy. These deficits were associated with a progressive increase in total tissue calcium content. The deficits were reversed, in part, by increasing extracellular calcium concentration. Whereas calmodulin and calcium-binding protein, as measured by radioimmune assay, did not change in amount, the activity of calmodulin, as a calcium-calmodulin activator of the enzyme 3',5'-cyclic nucleotide phosphodiesterase, declined progressively as the aluminum encephalopathy developed. Cholinergic neurochemical transmission, measured by choline acetyltransferase activity and muscarinic binding, did not change in the encephalopathy. We postulate that aluminum alters brain calcium homeostasis, perhaps through an effect on calmodulin.

Intramuscular desferrioxamine in patients with Alzheimer's disease.

Although epidemiological and biochemical evidence suggests that aluminium may be associated with Alzheimer's disease (AD), there is no convincing proof of a causal link for aluminium in disease progression. We have completed a two year, single-blind study to investigate whether the progression of dementia could be slowed by the trivalent ion chelator, desferrioxamine. 48 patients with probable AD were randomly assigned to receive desferrioxamine (125 mg intramuscularly twice daily, 5 days per week, for 24 months), oral placebo (lecithin), or no treatment. No significant differences in baseline measures of intelligence, memory, or speech ability existed between groups. Activities of daily living were assessed and videorecorded at 6, 12, 18, and 24 month intervals. There were no differences in the rate of deterioration of patients receiving either placebo or no treatment. Desferrioxamine treatment led to significant reduction in the rate of decline of daily living skills as assessed by both group means (p = 0.03) and variances (p less than 0.04). The mean rate of decline was twice as rapid for the no-treatment group. Appetite (n = 4) and weight (n = 1) loss were the only reported side-effects. We conclude that sustained administration of desferrioxamine may slow the clinical progression of the dementia associated with AD.