2 Kings 15:5:

And the LORD smote the king, so that he was a leper unto the day of his death, and dwelt in a several house.  And Jotham the king’s son was over the house, judging the people of the land.

Notes on 2 Kings 15:5:

2 Chronicles 26:16-21 explains this incident more fully.  The king’s sin was performing a function that only priests were authorized to perform.  As with the case of Uzzah, God showed that he does not take it lightly when a man knowingly mishandles the holy things of God.  The king’s pride caused him to take the things of God too lightly, a mistake that cost some of the Corinthians their lives in the New Testament (1 Corinthians 11:27-32).

See also:

Sickness as Chastening and Judgment in the Old Testament
Condition: Leprosy