The need to keep tons of things for "sentimental" reasons. The inability to get rid of anything. Usually involves the need to rent storage lockers, because every room in the house and basement is already filledwith sentimental knick-knacks and memorabilia.
When Jane moved out of her house, she needed to rent 3 storage lockers to store all of the things she couldn't part with. She suffered from Sentimental Retardation.