Decades before the first symptoms of Alzheimer's disease appear, some changes associated with the disease may begin to leave a trace in the blood. A study by the Sant Pau Research Institute (IR Sant Pau) has found that, in people with Down syndrome, levels of β-synuclein, a protein related to synaptic function, begin to rise in the third decade of life, long before symptoms appear and earlier than other blood biomarkers of Alzheimer's disease.