Iacono D, Volkman I, Nennesmo I, Pedersen NL, Fratiglioni L, Johansson B, Karlsson D, Winblad B, Gatz M.
Neuropathologic assessment of dementia markers in identical and fraternal twins.
Brain Pathol. 2014 Jul;24(4):317-33. Epub 2014 Mar 7
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What happens in two genetically identical brains after 98 years? What happens in the brains of two not genetically identical, but fraternal and opposite-sex twins after 79 years? What are the similarities and differences between two brains that at the beginning of their lives shared the same parental imprinting, similar social stimuli and environments, and equivalent nutrition, and then reached a life of eight, nine, or 10 decades long? The group of monozygotic and dizygotic twins analyzed in this study was diagnosed with dementia, mainly of Alzheimer’s disease (AD) type, as well as other medical conditions. Were the brain lesions associated with AD comparable between identical and fraternal twin brains? Were those AD lesions the only cerebral lesions present in their brains? What about their genotypes: Is the ApoE gene so important, and is it the only one? If there are differences in terms of brain pathology between genetically identical twins who died at the same age, what are the possible explanations?
These and other questions were the stimulating basis of this peculiar investigation. We had the unique opportunity to analyze a series of brains from monozygotic and dizygotic twins using the up-to-date clinical and pathologic criteria for Alzheimer’s dementia (AD). One of our several aims was to observe whether the brains from identical and fraternal twins could show more similarities, or pathologic concordances, in monozygotic (MZ) compared to dizygotic (DZ) twins. The study was performed on twin subjects, part of the Swedish Twin Registry and connected studies, who received periodic clinical and cognitive assessments before death, and an extensive neuropathologic assessment of multiple regions of the brain using immunohistochemistry techniques and semi-quantitative pathology scoring systems.
We hope that this investigation, unique in its genre, could offer new, unexplored, and intriguing views on the interaction among genetics, early social and environmental imprinting, education, and the possible pathologic changes, compensatory capacity, and plasticity phenomena of the central nervous system during normal and pathologic aging. We hope that this study will open new perspectives in human neuroscience, and that it will stimulate the entire medical and scientific community to consider those numerous and varied aspects of the gene-environment interaction that still need to be completely understood. Such future discoveries will probably shed light on what makes the human species so unique among mammals—so unique that its members will even donate their brains to investigate their own kind, as those twins and their families, to whom go our greatest recognition, generously did.
I thank the twins, their families, and the entire scientific team who made this investigation possible.