Familial lupus associated with a <i>P2RY8</i> variant: Navigating the boundary between monogenic disease and genetic susceptibility to lupus

Identification of a heterozygous P2RY8 E323G substitution in a father and son with cutaneous lupus and enhanced type I interferon signaling supports a role for P2RY8 in lupus causation and highlights the overlap between Mendelian disease and complex genetic susceptibility.