M05.07.02 Genetics

Medical students often encounter diseases with a suspected genetic component. Here, we explore the concept of concordance rates in twins and how family history can influence susceptibility to certain conditions.

Concordance Rates in Twins

Concordance rates refer to the probability that both twins in a pair will develop a particular trait or disease. Studying twins, especially monozygotic (identical) and dizygotic (fraternal) twins, allows researchers to disentangle the relative contributions of genetics and environment to complex traits.

Example: Alcoholism

Studies on alcoholism in twins demonstrate the interplay between genes and environment:

• Higher Concordance Rate in Monozygotic Twins: If one identical twin develops alcoholism, the other twin has a higher chance of developing it compared to a fraternal twin. This suggests a genetic predisposition.
• Environmental Influence: Twins born to alcoholic parents but raised by non-alcoholic parents have a lower chance of alcoholism compared to those raised by their biological alcoholic parents. This highlights the impact of environmental factors.

Family History and Disease Risk

Family history, which reflects the shared genes within a family, can influence the risk of developing certain conditions. For instance, a family history of alcoholism increases the likelihood of major depression in offspring. This doesn’t guarantee the offspring will develop depression, but it indicates a heightened susceptibility.

Key Points to Remember:

• Concordance rates in twins provide valuable insights into the genetic basis of complex traits.
• A higher concordance rate in monozygotic twins suggests a stronger genetic influence.
• Environmental factors can significantly modulate gene expression and influence disease risk.
• Family history can be a red flag for increased susceptibility to certain conditions.

Further Exploration

• National Center for Biotechnology Information National Institutes of Health (.gov)
• Online Mendelian Inheritance in Man (OMIM) (https://www.ncbi.nlm.nih.gov/omim)
• The American Society of Human Genetics (https://www.ashg.org/)pen_spark