My brother is seriously addicted to runescape. What should I do?

My brother is 12 and it's summer vacation at the moment. Every minute he's awake and on the computer, he always on the world of pixilated crap! Also as another result of his addiction he stopped eating and only eats when he's not on the computer so now he only eats twice. Also while I'm sleeping at times he always watches runescape videos on my phone.resulting in him waking up at 2 maybe 3 in the afternoon. He's a free uder now but he still goes on runescape for 5 or more hours. My mom barely notices because she said this only once "you play this game too much". The only time he goes out is when my mom forces him to go out and he hessitates to go out unless were going out to eat. I used to be addicted to this crap game but it wasn't at this degree. I still made good grades and friends but as for my bro, they went down. Hel'll be going to 7th grade when summer ends so I'm going to see how he does.