The SNCB gene provides instructions for making a protein called beta-synuclein. The exact function of this protein is unknown, but it is likely involved in a process called synaptic plasticity. Synaptic plasticity is the ability of the connections between nerve cells (called synapses) to change and adapt over time in response to experience. This process is critical for learning and memory. Beta-synuclein may also prevent harmful accumulation of a similar protein called alpha-synuclein in nerve cells (neurons).
At least two mutations in the SNCB gene have been found to cause dementia with Lewy bodies. This condition is characterized by intellectual decline (dementia); visual hallucinations; sudden changes in attention and mood; and movement problems such as rigidity of limbs, tremors, and impaired balance and coordination.
SNCB gene mutations lead to the production of a protein with impaired function. It is thought that this altered protein may not be able to prevent alpha-synuclein accumulation. A decrease in functional beta-synuclein likely results in alpha-synuclein accumulation and the formation of Lewy bodies. These abnormal protein clusters are present throughout the brain, where they impair neuron function and ultimately cause cell death. Over time, the loss of neurons increasingly impairs intellectual and motor function and the regulation of emotions, resulting in the signs and symptoms of dementia with Lewy bodies.