"Lewy body dementia is one of the most common forms of progressive dementia. People affected by this condition may experience a variety of symptoms such as changes in alertness and attention; hallucinations; problems with movement and posture; muscle stiffness; confusion; and/or memory loss. Although the exact cause of Lewy body dementia is poorly understood, symptoms are thought to result when clumps of a protein called alpha-synuclein (""Lewy bodies"") accumulate in the brain. Lewy body dementia usually occurs sporadically in people with no family history of the condition. Rarely, more than one family member may be affected."