It is just a Finnish saying meaning that you should blame your family if something is wrong, in the way it is with schizophrenia when you have inherited genes causing this illness.
There are also many other sayings we used when we were children such as *Harjamäen hurjat’ meaning the crazy people of Harjamäki. Harjamäki’s mental hospital is one famous mental hospitals in Finland but now it is a museum. My father and aunt visited there, basically got some mental treatment. My aunt is dead already, died at the age of 63, so young, she was schizophrenic.