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January 7, 2007

Genetics and Heredity, Other

Question from Wayland, Massachusetts, USA:

My 14-year-old was just diagnosed with type 1 in 2006. My eight-year-old daughter was diagnosed in 2004. Please explain how the percentage rate 3 to 5% can be accurate for a having a second child diagnosed when I know of at least FIVE other families in the local area, not including ourselves, that have two children with type 1. On top of it, my son has a different biological father which makes his chances of getting type 1 even smaller than the statistics. The percentage seems like it should be higher. Any insight as to why this occurred other than the "we just don't know?" What triggers it?

Answer:

You are asking a difficult individual question of genetics and comparing it to a general risk for a population. We know that the 3 to 5% figure is very stable for quite some time. In your particular family, what this all depends upon, of course, is which random genes were passed along from sperm and egg and then which of the known/unknown predisposing factors then “hit” such a susceptible person. There are some specific research efforts underway to try to answer such questions in what is called diabetes multiplex families (i.e., more than one person affected with type 1 diabetes) since we may get some clue to the specific gene locus. You should discuss this with your diabetologist and see about what might be considered and also who else in the family might share the same specific gene haplotypes so that their risk could also be assessed. With two siblings, if there is a third sibling, then subsequent risks rise closer to 5 to 10% and knowing if the HLA haplotypes are identical or non-identical would provide more specific genetic risk information.

SB