Beyond known PD genes <i>GBA1</i> and <i>LRRK2</i>, rare variants AD genes (<i>CD33</i>, <i>CR1</i> and <i>PSEN2</i>) and Aβ toxicity modifiers involved in RhoA/actin cytoskeleton regulation (<i>ARGHEF1, ARHGEF28, MICAL3, PASK, PKN2, PSEN2</i>) were shared risk factors across synucleinopathies. The gene discussed is ARHGEF28; the disease is Alzheimer disease.