. Twin pairs discordant for neuropathologically confirmed Lewy body dementia. J Neurol Neurosurg Psychiatry. 2009 May;80(5):562-5. PubMed.

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  1. The authors' speculation that environmental or epigenetic factors may underlie the discordance in monozygotic twins emphasizes the importance of epigenetic factors in the expression of disease phenotype. Indeed, the disappointments of genomewide association studies may have their roots in the overlay of epigenetic factors. We have evidence (submitted) of epigenetic differences in a pair of monozygotic twins discordant for AD.

  2. It is not necessary to speculate or postulate that environmental or epigenetic factors that underlie the discordance of AD or LBD expression in monozygotic twins. To explain phenotype variability among genetically identical individuals, stochastic expression of genes is the most sparing hypothesis, and was the one we were led to admit (Bruni et al., 1992) after discussion of environmental and other possible factors. Stochastic expression of genes, as a general biology rule, recently returned to the forefront, at least in Europe; an interesting symposium was devoted to it (Kupiec et al, 2009).

    See also:

    Kupiec JJ et al (eds.): Le hasard au coeur de la cellule, 1vol 192pp, Paris Editions Syllepse, 2009).

    References:

    . Alzheimer's disease: a model from the quantitative study of a large kindred. J Geriatr Psychiatry Neurol. 1992 Jul-Sep;5(3):126-31. PubMed.

  3. In the absence of other alternatives, stochastic models of gene expression may be constructed to describe available data. Epigenetic influences on gene expression is a widely explored field, in basic biology and especially also in cancer. A Cold Spring Harbor Laboratory book titled Epigenetics by Allis et al. provides the basics of epigenetic influences on gene expression.

    Epigenetic/environmental influences on phenotypic expression of AD is a young, developing field that is accumulating evidence. See papers by Fuso and Scarpa and by Mastroeni et al. as examples of evidence for epigenetic modulation of phenotypic expression of AD.

    References:

    . Changes in Presenilin 1 gene methylation pattern in diet-induced B vitamin deficiency. Neurobiol Aging. 2011 Feb;32(2):187-99. PubMed.

    . Epigenetic changes in Alzheimer's disease: decrements in DNA methylation. Neurobiol Aging. 2010 Dec;31(12):2025-37. PubMed.