Michael J. Fox and wife Tracy Pollan are expecting their fourth child, the couple's spokeswoman has told PEOPLE. Pollan is four months pregnant. "They are extremely excited and she feels great. She is glowing. They are extremely happy," the spokeswoman said, adding that the news is a "wonderful birthday present for both of them." (Fox, who made PEOPLE's Most Intriguing list in 2000, turns 40 in less than two weeks, and Pollan turns 41 on June 22.) The couple, married since 1988, has one son, Sam Michael, 12, and twin daughters, Aquinnah Kathleen and Schuyler Frances, 6. Fox, an avowed family man, left Spin City in 2000 to focus on those he loves and a cause he cares about: Parkinson's disease, from which he suffers. "My family is the reason I live, not the work," he told PEOPLE last year. "You could bring back Olivier from the dead and have him perform Hamlet and I would be at home with my family."