Interesting results, but I would be careful with probabilities. It may indeed be very rare that 4 people from this forum have two of the same bad genes. But to really know if that is a rare event, we must know the probability of any four people having any two bad genes in common.

Given 23andMe gives data on about 600,000 genes, and the average amount of bad genes in a person is 400 [1], what is the probability of four people having at least two of the same bad genes?

It's a hard math problem for sure. It might be solvable by thinking in terms of card decks. It's like if you had four card decks and picked n cards from each deck, what is the probability of the at least m cards being the same in each hand?

1. https://www.npr.org/sections/health-sho ... awed-genes