D. R. Crapper McLachlan

Alzheimer's disease in Down's syndrome: Clinicopathologic studies

Clinical and neuropathologic evidence points to the development of Alzheimers disease (AD) in seven Downs syndrome patients above age 40. Dementia was observed in these patients over periods of 2.5 to 9.2 years. The first clinical sign of AD, visual memory loss, was succeeded by impaired learning capacity and decreased occupational and social functioning, and culminated in seizures and urinary incontinence. The morphometric observations of the brains of these seven patients with AD showed that the numbers of plaques and tangles exceeded 20 per 1.5 × 106 μm2 area, in both the prefrontal and hippocampal cortices. Plaques and tangles were also evident in the basal ganglia, thalamus, hypothalamus, and midbrain. In addition, we found that four of the seven brains showed small strokes, and five of the seven amyloid angiopathy. This study also indicates that by longitudinal neuropsychological evaluations and lab tests, which exclude other causes of dementia, the diagnosis of AD can be made even in severely and profoundly retarded patients.

Aluminum and Alzheimer's Disease

There is now substantial evidence indicating that an accumulation of aluminum occurs in grey matter in diseases associated with Alzheimer neurofibrillary degeneration. Four principle sites of aluminum accumulation have been identified in Alzheimers disease: DNA containing structures of the nucleus, the protein moieties of neurofibrillary tangles, the amyloid cores of senile plaques and cerebral ferritin. Consideration of the extensive information now available on the toxic effects of aluminum in these four loci strengthens the hypothesis that aluminum could be important in the pathogenesis of this neurodegenerative process. The evidence, however, does not support an etiological role for aluminum in Alzheimers disease. The primary pathogenic events responsible for Alzheimers disease are presumed to have affected the genetically determined barriers to aluminum resulting in increased amounts of this toxic element to vulnerable target sites.

Molecular and prospective phenotypic characterization of a pedigree with familial Alzheimer's disease and a missense mutation in codon 717 of the β‐amyloid precursor protein gene

We present prospective clinical and neuropathologic details of a pedigree segregating familial Alzheimers disease (FAD) associated with a mutation (G→A substitution) at nucleotide 2149 in exon 17 of the amyloid precursor protein (APP) gene. This mutation, which is predicted to cause the missense substitution of isoleucine for valine at codon 717 of APP, cosegregated perfectly with the FAD trait (lod score = 3.49 at = 0.00). The earliest clinical manifestations of the disease relate to deficits in memory function, cognitive processing speed, and attention to complex cognitive sets. These changes occurred in the absence of changes in nonmemory language and visuospatial functions. The neuropathologic features of FAD associated with the APP717 mutation in this family include severe neuronal loss, abundant neurofibrillary tangles, amyloid plaques, and amyloid angiopathy. These results provide independent confirmation that mutations in the APP gene are linked to the FAD trait in some families.

New Evidence for an Active Role of Aluminum in Alzheimer's Disease

Application of molecular biological techniques and sensitive elemental analysis have produced new evidence implicating aluminum as an important factor in down regulation of neuronal protein metabolism. Aluminum in Alzheimers disease may act by electrostatically crosslinking proteins, particularly the methionine containing histone H1(0), and DNA. The consequence of such crosslinking is reduced transcription of at least one neuron specific gene, the low molecular weight component of neurofilaments. In the superior temporal gyrus in Alzheimers disease, down regulation of this gene occurs in approximately 86% of surviving neurons and, therefore, aluminum must be considered as having an active role in the pathogenesis. Epidemiological studies are reviewed that independently support the hypothesis that environmental aluminum is a significant risk factor. Preliminary evidence also suggests that a disorder in phosphorylation may be an important initiating factor.

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 dernented [NAD; 3 Huntingtons 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.

Characterization of Messenger RNA from the Cerebral Cortex of Control and Alzheimer‐Afflicted Brain

Abstract: 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 simples. Heatshock 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.

Changes in chromatin structure associated with Alzheimer's disease.

Abstract— The enzyme micrococcal nuclease was used to examine the accessibility of chromatin extracted from brains of 13 patients with senile and presenile dementia of the Alzheimer type. Compared with chromatin extracted from brains of 8 patients without neurological signs or brain pathology and brains of 7 patients with nonAlzheimer dementia, Alzheimer chromatin was less accessible to this enzyme‐. Reduced accessibility was reflected by a reduced yield of mononucleosomes in comparison with dinucleosomes and larger oligomers. Both neuronal and glial chromatin were found to be similarly affected. The reduced yield of mononucleosomes from Alzheimer chromatin is not due to their increased breakdown, but is probably related to protein associated with the internucleosomal linker region that retards nuclease action. Dinucleosomes isolated from control and Alzheimer nuclease digests were examined for their protein complement. Three perchloric acid‐soluble proteins situated in the histone HI region of sodium dodecyl sulfate (SDS) gels were present in elevated levels in Alzheimer dinucleosomes. These results represent the first example of altered chromosomal proteins associated with a diseased state of the brain.

Analysis of the functional effects of a mutation in SOD1 associated with familial amyotrophic lateral sclerosis

Mutations in the Cu, Zn superoxide dismutase (SOD1) gene have been reported in some pedigrees with Familial Amyotrophic Lateral Sclerosis (FALS). We have investigated the functional and structural effects of a Gly-->Ser mutation at codon 41 of SOD1 in a pedigree with FALS and the topography of SOD1 expression in the mammalian CNS. These analyses show that the 41Gly-->Ser mutation causes a 27% reduction in Cu, Zn SOD activity. SOD1 is transcribed at high levels in rat motoneurons and four other types of neurons homologous to upper motoneurons that degenerate in human ALS. However, SOD1 is transcribed at lower levels in other types of neurons, such as cerebellar Purkinje cells, which are not usually involved significantly in human ALS. On the other hand, immunocytochemical studies indicate that most types of rat neurons contain similar levels of Cu, Zn SOD immunoreactive protein. Nevertheless, these results suggest that the essential feature causing this subtype of ALS is either a reduction in Cu, Zn SOD activity in cell types that presumably critically require Cu, Zn SOD for protection against oxidative damage or the fact that the mutation in SOD1 associated with FALS results in a novel gain of function that is particularly deleterious to those cell types expressing SOD1 at high levels.

Selective messenger rna reduction in alzheimer's disease

The relative abundance of 7 messenger RNAs extracted from Alzheimer and control neocortex were examined by Northern and quantitative dot blot analysis. The average yield of mRNA coding for NF-L, the 68-kDa moiety of neurofilament protein, was reduced to 27% of control when expressed as the percentage of total RNA or 14% when expressed per gram of neocortex. In contrast, the yields of 6 other messenger RNAs fell into two categories: those which were statistically significantly reduced to about 65% of control and those which were not reduced when expressed as percentage of total RNA. The anomalous low abundance of neuron specific NF-L mRNA, coding for the lowest molecular weight moiety of neurofilament proteins, in cerebral cortex of Alzheimers disease cannot be adequately accounted for by a non-specific effect of brain damage, neuron cell loss or neurons with neurofibrillary degeneration. We speculate that this mRNA decrease is related to a functional deficit of gene expression in Alzheimers disease, perhaps related to the non-random increase in chromatin compaction previously reported from this laboratory. The inability of neurons to maintain homeostatic amounts of NF-L transcription products may be linked to the accumulation of abnormal filamentous components characteristically associated with the diseased cytoskeleton.

SOD1 missense mutation in an Italian family with ALS

We have discovered a new Italian pedigree with autosomal-dominant ALS. The pedigree, at present, comprises 75 members distributed in five generations. ALS was diagnosed in eight patients. The mean ± SD age of onset of the disease was 46.8 ± 13.5 years, with a range of 29 to 63 years. The mean ± SD duration of the disease was 11.6 ± 1.7 months. Molecular genetic studies showed a missense mutation (Gly→Ser, codon 41) in exon 2 of the Cu/Zn superoxide dismutase gene (SOD1) on chromosome 21 in the available affected member and in 45% of the at-risk subjects of the pedigree. This study confirms the presence of SOD1 point mutations in families with autosomal-dominant ALS and suggests that additional genetic or environmental factors may be involved in the full expression of the disease.