I just had to get this off my chest.

[Evil Yoshi Toes]

I wouldn't say that, I think he's just a short guy. In all the games where powerups don't appear, he is at his "super" size, so I'd say that is his natural height. That still makes him short, but I don't think he's short enough to be considered to have a medical condition. If you're comparing him to the men and women of New Donk City, perhaps Mushroom Kingdom folk are just naturally shorter because next to them Princess Peach is quite short too.