How come I have pseudogout, but nobody else in the family has it?

Not all genetic. Pseudogout can be present for a lot of reasons besides genetic. Pseudogout is an inflamamtory arthritis caused by the deposit of calcium pyrophosphate dihydrate crystals. This can occur with age, with thyroid disease, with increased production of the parathyroid hormone - ie hyperparathyroidism, but most is unknown. These crystal accumulate in the joint and cause inflammation.