Alzheimer's disease in twins

Area of Science:

• Neuroscience
• Genetics
• Epidemiology

Background:

• Genetic susceptibility to Alzheimer's disease (AD) extends beyond familial cases, with sporadic AD often linked to apolipoprotein E polymorphism.
• Age and environmental exposures are key determinants of AD penetrance.
• Twin studies are crucial for dissecting gene-environment interactions in complex diseases like AD.

Purpose of the Study:

• To review and analyze existing twin studies on Alzheimer's disease.
• To evaluate methodologies for assessing genetic and environmental contributions to AD.
• To discuss sampling strategies and potential biases in AD twin research.

Main Methods:

• Comparison of concordance rates between monozygotic (MZ) and dizygotic (DZ) twins to estimate genetic and environmental influences.
• Application of genetic models to quantify contributions from genetic, shared, and unique environmental effects.
• Utilizing co-twin control studies to investigate environmental factors in discordant twin pairs.

Main Results:

• Concordance rates for AD in MZ twin pairs have shown significant variability, ranging from 31% to 83% in published studies.
• The review highlights a limited number of co-twin control studies, with only one published study on twins discordant for AD.
• Existing AD twin research often relies on case reports or selected patient materials, indicating potential sampling biases.

Conclusions:

• Twin studies provide valuable insights into the complex interplay of genetic and environmental factors in Alzheimer's disease.
• Further robust twin research, particularly co-twin control studies, is needed to clarify the specific roles of environmental exposures in AD etiology.
• Standardized sampling methods are essential to mitigate biases and enhance the reliability of findings in AD twin research.