Mitochondrial DNA variants in inclusion body myositis.

Mitochondrial DNA variants have been shown to be associated with many diseases. Mutations at mitochondrial DNA nucleotide positions 3192, 3196, 3397 and 4336 have been described in association with late-onset Alzheimer's disease. The pathological similarities between inclusion body myositis and Alzheimer's disease prompted an analysis of the relationship between the reported mutations and sporadic inclusion body myositis. The 4336G variant was not significantly increased in patients with inclusion body myositis or Alzheimer's disease when compared to controls. None of the patients with inclusion body myositis carried mutations at nucleotide positions 3192, 3196 and 3397. A transition at nucleotide position 4580 was detected in some patients with inclusion body myositis and Alzheimer's disease but was not significantly higher in frequency when compared to controls. Phylogenetic analysis showed that the 4336G and 4580A variants clustered together in their respective group. A group of patients with inclusion body myositis also clustered together on a separate branch of the phylogenetic tree. Closer investigation of this group revealed a common polymorphism at nucleotide position 16311. The frequency of the 16311C variant was higher in inclusion body myositis than in Alzheimer's disease and controls, although when only caucasian patients were considered the increased frequency was not statistically significant. Further studies will be required to determine whether this variant plays a role in the pathogenesis of inclusion body myositis.

Insulin effects on glucose metabolism, memory, and plasma amyloid precursor protein in Alzheimer's disease differ according to apolipoprotein-E genotype.

Higher fasting plasma insulin levels and reduced CSF-to-plasma insulin ratios, suggestive of insulin resistance, have been observed in patients with Alzheimer's disease (AD) who do not possess an apolipoprotein E (ApoE)-epsilon 4 allele. Insulin has also been implicated in processing of beta-amyloid and amyloid precursor protein (APP). We examined the effects of intravenous insulin administration while maintaining euglycemia on insulin-mediated glucose disposal, memory, and plasma APP in patients with AD and normal adults of varying ApoE genotypes. AD subjects without an epsilon 4 allele had significantly lower insulin-mediated glucose disposal rates than did AD patients with an epsilon 4 allele (p < 0.03) or than did normal adults without an epsilon 4 allele (p < 0.02). AD subjects without an epsilon 4 allele also showed significant memory facilitation with insulin administration (p < 0.04), whereas the AD-epsilon 4 group did not. Insulin reduced APP levels for AD patients without an ApoE epsilon 4 allele, but raised APP for AD patients with an ApoE epsilon H4 allele These results document ApoE-related differences in insulin metabolism in AD that may relate to disease pathogenesis.

The effect of insulin and glucose on the plasma concentration of Alzheimer's amyloid precursor protein.

The deposition of beta amyloid is a critical event in the pathogenesis of Alzheimer's disease. This peptide is a metabolite of the amyloid precursor protein. Recent research suggests that there is a correlation between plasma insulin and glucose concentrations and memory performance in Alzheimer's disease sufferers. Additionally, in vitro evidence suggests that both insulin and glucose may affect the metabolism of amyloid precursor protein and therefore the production of beta amyloid--however, to our knowledge no in vivo data have yet been published. We investigated the effect of elevated plasma levels of glucose and insulin on the plasma concentration of amyloid precursor protein in non-Alzheimer's disease subjects. As would be expected following ingestion of a glucose drink, blood insulin and glucose levels significantly increased. Interestingly, however, plasma amyloid precursor protein concentration decreased. Whilst no correlation was observed between insulin or glucose levels and plasma amyloid precursor protein concentration, the decrease in plasma amyloid precursor protein concentration was affected by the apolipoprotein E genotype of the subject. Possession of an epsilon4 allele resulted in a reduced decrease in plasma amyloid precursor protein in response to glucose ingestion when compared to non-epsilon4 subjects. We conclude that glucose ingestion, and the subsequent elevation of plasma levels of glucose and insulin leads to a decrease in plasma amyloid precursor protein concentration. Further studies are required to determine the clinical significance of these physiological changes in plasma amyloid precursor protein and the implications for Alzheimer's disease pathogenesis.