Autosomal Dominant Inheritance

In the diagram below, the two chromosomes of each parent are shown.  Also shown is the gene for Gorlin syndrome - the faulty gene is coloured in red, the "normal" genes in white.  As can be seen, each child of a with the syndrome inherits either the faulty or the normal gene from the parent with the syndrome.

Autosomal Dominant Inheritance diagram

But why am I the only person affected in my family?

In some families, only one person appears to be affected.  This could be because his or her mother or father had the syndrome, but the effects were so mild that it was never diagnosed.  An alternative possibility is that the fault in the gene causing Gorlin syndrome happened for the first time in that family in the egg or sperm which went to make the person.  This is called the result of a "new mutation" and we know that this happens fairly frequently to the Gorlin syndrome gene.  The children of someone who is the first person to be affected can inherit the faulty gene, of course, with the risks shown above.  However, other members of the family (parents and brothers and sisters of the affected person) may not be at risk of the condition, and not need screening for the basal cell carcinomas or jaw cysts. Referral to a genetics department may be helpful in deciding this.  

DNA tests - by looking directly at the mutation in the gene - may prove that someone's disease is the result of a new fault, occurring for the first time in him or her.

Diagram and information provided by Prof Peter A Farndon, MD, FRCP

Next Review January 2017

 Originally produced by Professor P. A. Farndon, Clinical Geneticist, Jim Costello (deceased) and Margaret Costello.  We are reliant on a team of medical advisors for the clinical content of the website. We are grateful for their continuing support. 
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