This depends on which sexually transmitted infection (STI) you have. Some STIs cause few or no symptoms, so you may not know you have one.
I believe the answer you are looking for is the excretory system.
Genes in the DNA tell the cells which proteins to produce, which determines certain traits
Mental illness itself occurs from the interaction of multiple genes and other factors -- such as stress, abuse, or a traumatic event -- which can influence, or trigger, an illness in a person who has an inherited susceptibility to it.
