In terms of finding issues caused by multiple mutations, it isn't so much a case of not having enough computing power - instead, it is about having enough patie

In terms of finding issues caused by multiple mutations, it isn't so much a case of not having enough computing power - instead, it is about having enough patients with the same condition that gives enough statistical power to say for sure that these variants are the cause. Humans are extremely variable. If I do whole-genome sequencing on a random person, I'll find probably 3 million places in their DNA where they differ from the average Joe. 90% of those are common variants, and we can filter those out because we know they are common, but that still leaves on the order of 300,000 variants that are rare, the vast majority of which cause absolutely nothing. We already diagnose conditions caused by two mutations - they are called compound heterozygous, because there are two heterozygous mutations, one on each copy of a particular gene, therefore clobbering both copies and causing disease. We have very very few conditions where we know that mutations on multiple genes are required for disease - they are simply too hard to look for, as we don't have enough people in the world to get the statistical power.