The Chuck Cunningham Syndrome

What is the Chuck Cunningham Syndrome? Have you ever noticed when a character from a TV show disappears without any explanation? No doubt you remember that on Happy Days there was Ritchie Cunningham and his younger sister Joanie. If you haven't seen the first season of the show there's a good chance that you didn't know that Ritchie had an older brother. Chuck seems to have disappeared without further mention during the rest of the long run of the series. Even in the final episode of Happy Days Howard Cunningham says something along the lines of "we've raised two wonderful children". Was Chuck not "wonderful", or perhaps he was disowned? Or maybe just a dream? Practically the same thing happened earlier on My Three Sons. There was an older brother Mike followed by Robbie and Chip. During the first color episode of the series (I believe it was) we see Mike get married and go on his marital way. Not only was he never seen again but he was never mentioned again either except for maybe a few episodes (if any) that followed the wedding episode. And his "nonexistence" was verified in a later season when a lady saw a picture of the family (minus Mike) in the office of the father Steve Douglas. Trying to find out if he had a wife she asked him if that was his whole family and he replied "That's it". I supposed the eldest son was disowned for getting married!

Here's a detailed article on the Chuck Cunningham Syndrome, although they fail to mention My Three Sons.