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Colin MacKenzie M.D.
November 15, 2020

Alcohol Quiz #2

A. John’s adoptive parents never drink alcohol; therefore, his risk of alcoholism can be no greater than average.

  1. True
  2. False

B. Jim has a dizygotic (fraternal) twin named Bill.  Tom has a monozygotic (identical) twin named John.  Each set of twins has parents that are both alcoholic.  There is no difference in risk for alcoholism between Jim and John (all other things being equal). 

  1. True
  2. False

C. Susan has a dizygotic (fraternal) twin named Sarah.  Tom has a monozygotic (identical) twin named John.  Susan & Tom have alcoholism.  Sarah and John both carry the same risk of developing alcoholism (all other things being equal).

  1. True
  2. False

D. Susan has a dizygotic (fraternal) twin named Sarah.  Tom has a dizygotic twin named John.  Susan & Tom have alcoholism.  The risk that Sarah will develop alcoholism is the same as John.

  1. True
  2. False

Answers: 

A. False.  Adopted children of (biological) alcoholic parents still maintain a higher risk of developing alcoholism even if they are raised by parents who do not use alcohol. This risk can be 300% to 400% greater than baseline variable risk. 

B. True. Each twin from either set has the same risk of alcoholism given that they all have the same risk of inheriting “at risk” genes. 

C. False. Since monozygotic twins carry an identical set of genes, the risk that John will develop alcoholism is greater than Sarah’s risk.  In addition, male monozygotic twins carry a higher risk than female monozygotic twins.  Male monozygotic twins have an alcoholism concordance rate of 50% whereas female monozygotic twins have a concordance of 30%. 

D. False. Among dizygotic twins, male twins carry a concordance rate of 33% while female dizygotic twins have a risk of 16%.