MadSci Network: Genetics

Re: are birth marks hereditary

Date: Mon Oct 2 16:42:51 2000
Posted By: Christopher Carlson, Ph.D.
Area of science: Genetics
ID: 969429951.Ge

Good question.  There are actually two facets to your question, and I will 
answer them in turn.  First, is the occurrence of birthmarks hereditary?  
Depends on the type of birthmark.  There are several types of birthmark, 
generally named for what they look like.  These include cafe au lait 
birthmarks, which are browner than the surrounding skin, red wine birthmarks 
which are red but smooth (like Mikhail Gorbachev's) and strawberry 
birthmarks, which are red and raised.  

Some rare hereditary conditions correlate with specific types of birthmark, 
but most birthmarks are sporadic.  For example, people with the rare 
disorder neurofibromatosis usually have cafe au lait spots, but people with 
cafe au lait spots are unlikely to have neurofibromatosis.  There are also 
hereditary syndromes where individuals are predisposed to have moles on 
their skin, but most people with moles do not have these syndromes. 

The second facet of your question is whether the location/shape of 
birthmarks is hereditary.  In general the answer to this question is also 
negative: sporadic birthmarks generally represent a somatic mutation which 
occurred as an individual grew from an embryo.  The affected region 
represents all the cells descended from the single cell where the mutation 
originally occurred.  Thus, a mutation early in embryogenesis can affect a 
large area on a person's body, while a late mutation will affect a 
proportionately smaller area.  However, because the mutation happened at 
random during development, the likelihood that any two individuals will have 
exactly the same birthmark is pretty small.  Kind of like snowflakes.  If 
you look at your birthmark and compare it with your father's, I will bet 
that you will find subtle but significant differences between them.

Nonetheless, it is pretty cool that you've got a similarly placed/shaped 
birthmark.  Just don't count on your kids having the same thing...

	Chris Carlson

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