Apolipoprotein E polymorphism, homocysteine serum levels and hippocampal volume in patients with alcoholism: an investigation of a gene-environment interaction

Components of the choline oxidation pathway modify the association between the apolipoprotein ε4 gene variant and cognitive decline in patients with dementia

BACKGROUND

Metabolites involved in one-carbon metabolism (OCM) may predict cognitive prognosis in dementia. The link between OCM, apolipoprotein E (APOE), and DNA methylation creates a biologically plausible mechanism of interaction.

AIM

To assess OCM metabolites as predictors of 5-year cognitive prognosis in patients with mild dementia, and in subgroups defined by the APOEε4 allele variant.

METHODS

We followed one-hundred and fifty-two patients with mild dementia (86 with Alzheimer's disease, 66 with Lewy body dementia, including 90 with at least one APOEε4 allele) for 5 years with annual Mini-Mental State Examinations (MMSE). Total homocysteine, methionine, choline, betaine, dimethylglycine, sarcosine, folate, cobalamin and pyridoxal 5'-phoshate were measured in serum at baseline. We used linear mixed models to assess metabolite-MMSE associations, including 3-way interactions between metabolites, time, and APOEε4. False-discovery rate adjusted p-values (Q-values) are reported.

RESULTS

Metabolite concentrations were not different in patients with dementia according to the presence of APOEε4. Overall, serum concentration of total homocysteine was inversely associated with MMSE performance, while betaine was positively associated with MMSE (Q < 0.05), but neither was associated with MMSE decline. Serum concentrations of betaine, dimethylglycine and sarcosine, however, were associated with slower MMSE decline in patients with APOEε4, but with faster MMSE decline in patients without the allele (all 3-way interactions: Q < 0.05).

CONCLUSION

Components of the choline oxidation pathway are associated with a better cognitive prognosis in APOEε4 carriers and a worse cognitive prognosis in non-carriers. Further research investigating targeted metabolic interventions according to APOE allele status is warranted.

Apolipoprotein E epsilon 4 allele is associated with ventricular expansion rate and surface morphology in dementia and normal aging

The apolipoprotein E epsilon 4 allele (ApoE-ε4) is the strongest known genetic risk factor for late onset Alzheimer's disease. Expansion of the lateral ventricles occurs with normal aging, but dementia accelerates this process. Brain structure and function depend on ApoE genotype not just for Alzheimer's disease patients but also in healthy elderly individuals, and even in asymptomatic young individuals. Therefore, we hypothesized that the ApoE-ε4 allele is associated with altered patterns of longitudinal ventricular expansion, in dementia and normal aging. We tested this hypothesis in a large sample of elderly participants, using a linear discriminant analysis-based approach. Carrying more ApoE-ε4 alleles was associated with faster ventricular expansion bilaterally and with regional patterns of lateral ventricle morphology at 1- and 2-year follow up, after controlling for sex, age, and dementia status. ApoE genotyping is considered critical in clinical trials of Alzheimer's disease. These findings, combined with earlier investigations showing that ApoE is also directly implicated in other conditions, suggest that the selective enrollment of ApoE-ε4 carriers may empower clinical trials of other neurological disorders.

Homocysteine, neural atrophy, and the effect of caloric restriction in rhesus monkeys

Higher serum homocysteine (Hcy) levels in humans are associated with vascular pathology and greater risk for dementia, as well as lower global and regional volumes in frontal lobe and hippocampus. Calorie restriction (CR) in rhesus monkeys (Macaca mulatta) may confer neural protection against age- or Hcy-related vascular pathology. Hcy was collected proximal to a magnetic resonance imaging (MRI) acquisition in aged rhesus monkeys and regressed against volumetric and diffusion tensor imaging indexes using voxel-wise analyses. Higher Hcy was associated with lower white matter volume in pons and corpus callosum. Hcy was correlated with lower gray matter volume and density in prefrontal cortices and striatum. CR did not influence Hcy levels. However, control monkeys exhibited a strong negative correlation between Hcy and global gray matter, whereas no relationship was evident for the CR monkeys. Similar group differences were also seen across modalities in the splenium of the corpus callosum, prefrontal cortices, hippocampus, and somatosensory areas. The data suggest that CR may ameliorate the influence of Hcy on several important age-related parameters of parenchymal health.

Proton magnetic resonance spectroscopy in alcohol use disorders: a potential new endophenotype?

BACKGROUND

Current effort is directed at defining new classification schemes for alcohol use disorders (AUD) based on genetic/biological, physiological, and behavioral endophenotypes.

METHODS

We describe briefly findings of in vivo brain proton magnetic resonance spectroscopy ((1)H MRS) studies in AUD and propose that they be further explored and expanded regarding their value as a potential endophenotype for AUD.

RESULTS

In vivo (1)H MRS, as part of the emerging field of "imaging genomics," may provide readily accessible, objective, functionally significant and region-specific neurobiological measures that successfully link genotypes to neurocognition and to psychiatric symptomatology in relatively small patient cohorts. We discuss several functional gene variants that may affect specific (1)H MRS-detectable metabolites and provide recent data from our own work that supports the view of genetic effects on metabolite measures.

CONCLUSIONS

MRS-genetics research will not only offer clues to the functional significance and downstream effects of genetic differences in AUD, but, via monitoring and/or predicting the efficacy of pharmacological and behavioral interventions as a function of genotype, has the potential to influence future clinical management of AUD.