The Mendelian Calculator uses the family history to calculate the probability of a case already known to have a condition inheriting that condition according to a particular inheritance pattern as opposed to having sporadic disease. It also calculates sensitivity, specificity and likelihood ratios for observing a particular inheritance pattern given a certain family composition.

In a typical clinical setting, we may often be faced with a patient in whom we suspect an underlying inherited disease. Does a lack of a family history make this diagnosis much less likely? How much less likely? How much does the family size and make-up, and the penetrance and inheritance pattern of the disease affect this likelihood?

Conversely, if the patient actually has a family history that fits the criteria for a particular inheritance pattern, how specific is this for that pattern as opposed to another inheritance pattern? How much does it make sporadic disease less likely?

Input the family composition, affected and unaffected members, and the suspected inheritance pattern, prevalence and penetrance, and the app provides probabilities, predictive values, sensitivities, specificities and likelihood ratios.