The Nazi's wanted to kill anybody who had diseases that they considered hereditary. This included mental illnesses, learning disabilities, physical deformities, epilepsy, blindness, deafness, severe alcoholism, and asociality. They thought that killing these people would be the next step in creating the aryan master race and called these people "life unworthy of life", "useless eaters", and pointed out their burden upon society. They were killed under the T4 program and it's estimated by the end of the war about 275,000 people with disabilities had been killed, mostly by poisonous gases.
Badge for asocials
Nazi propaganda poster saying how much a disabled person costs to care for.