Why does the CanRisk Tool sometimes fail to process pedigrees with loops?
On most occasions, the CanRisk Tool will generate an error message when you attempt to process a pedigree that contains a loop (for example where two brothers in one nuclear family marry two sisters in another nuclear family). Loops make the risk calculations more complex which increases memory usage and runtimes, and so these calculations might fail.
Unfortunately, there is no direct workaround for this. Users can try to build the pedigree without the loop and run the risk calculation. However, this may result in some inaccuracy in the predicted risks. As a result, the risks given when ignoring loops should be treated as indicative risks.
Users should try to break the loop as farther away as possible from the proband, to minimize the resulting inaccuracy. Also, when breaking the loop, it might be worth duplicating the (shared) family history on the two individuals whose link has been severed.
