There is a disease that was thought to be genetic, but was ultimately traced to ritual cannibalism spreading an infection. Relatives would eat the dead and what body part you got depended upon how closely related you were. This caused the disease to very much mimic a genetic disorder in its pattern of dispersal throughout the family.

"Runs in families" needs to be very clearly distinguished from genetic disorders per se. The former suggests correlation with an as yet unidentified cause or causes, as there may be various contributing factors. The latter is a case of identified cause.

Easy enough to confuse if your own life does not depend upon it, but absolutely not the same thing.