John 9:3

But that the works of God should be made manifest in him

(αλλ' ινα φανερωθη τα εργα του θεου εν αυτω). Jesus denies both alternatives, and puts God's purpose (αλλ' ινα with first aorist subjunctive of φανεροω) as the true solution. It is sometimes true that disease is the result of personal sin as in the man in John 5:14 and parents can hand on the effects of sin to the third and fourth generations, but there are cases free from blame like this. There is comfort for many sufferers in the words of Jesus here.