Brent was on his way to work when he vomitted and decided to return home. When he arrived, he found his wife having a seizure in the bathtub and Mikey underwater not moving.
He called 911 and both his wife and son were rushed to Princeton-Plainsboro Teaching Hospital. Luckily, Mikey had not suffered any major injury and merely required supportive care. However, Kara was much sicker.
Despite Chase's best efforts, Mikey died. House couldn't figure out why - Mikey didn't seem to be that badly injured and simply failed to improve with treatment. He suddenly realized that the drug Mikey would have been treated with contains gluten as a binder, which is dangerous for infants with celiac disease. If Kara had it too, it would explain most of her symptoms and a related stomach cancer would explain the others.
House needed to do an autopsy on Mikey, but Brent was still cradling his body and refused consent. House finally confronted Brent about his own alcohol use and how he probably ignored the signs of his wife's increasing problems. Brent finally agreed to the autopsy.
However, although the autopsy confirmed celiac disease, Kara refused treatment for the cancer. Despite what his wife had done, Brent was still upset that she refused treatment.