Alzheimer’s

Forgetfulness, confusion, loss of energy, rigidness in behavior

From D&D Wiki

Name: Alzheimer’s Disease (‘Ex’)
Infection DC: Character’s age minus 60
Incubation: 2d10 years
Damage: After infected, save every year at DC 10. For each failed save receive, 1d3 Intelligence, 1d3 Wisdom, 1d3 Charisma permanent HP damage. After Wisdom and Intelligence scores are half of the character’s original scores, the character must save every year at DC 15 or suffer from the effects of the insanity spell. All effects can only be cured by a lesser wish or greater.