+6 characteristic
+1 improved swordmage wardind (Arcane power)
+1 greater swordmage warding (Arcane power)
It's worth noting that to pull this off as a genasi he'd have to start with 12 str, 12 dex, and 20 int. This would leave 2 points, so he probably had a 12 con which would now be a 15. He'd have been better off ditching improved swordmage warding, grabbing Hide Armor proficiency, lowering his dex and raising his con. As it is, he's behind the defender game on healing surges and hp, his mark is less useful (assuming he took shielding), and the handful of swordmage powers that use con for secondary effects are less useful. This also confirms that his Will is based on an 11 in his best will stat.
As others have mentioned, using a variety of enemies will mean that some will target non-AC defenses and your player will be worse than other defenders against them due to hp/healing surge issues.
Tangent:
Honestly, I think the Swordmage is the only defender that does what I'd like defenders to do. In most groups I've seen, the defender has the same AC as the strikers and a point or two over the others and probably has about 2+1/level more hp. And that's assuming the Defender can secondary con and the other character doesn't use con for primary or secondary. Swordmages tend to have high AC and can move around enough to put the enemy in a no-win scenario. Against anyone else, the enemy should probably just attack the defender. I know that sounds like a victory for the defender (he's doing his job, yay!), but the group is getting almost 0 advantage from the defender taking the hits because his defenses and hp are pretty much the same. I mean sure if you have a controller that doesn't secondary con, he might actually need some defending, but that's pretty rare.
Defenders should have significantly higher defenses and hp than the rest of the group, area attacks shouldn't ignore marks (i.e. defenders should get to punish enemies that want to use area attacks even if they include the defender so that the defender's role can be enlarged), and their absence should be noticeable in the way a leader's absence is.