"just a description of some symptoms." Yes - all psychological disorders are syndromal. None are purely genetic or environmental, in fact the DSM and and ICD e

"just a description of some symptoms." Yes - all psychological disorders are syndromal. None are purely genetic or environmental, in fact the DSM and and ICD explicitly rule out psychosis or positive schizophrenic like symptoms caused by say toxin poisoning from their diagnostic criteria. What we can do is heritability studies on those who do fit the diagnostic criteria. We can test their relatives on neurocognitive batteries, including twin studies and get quite an accurate picture of the level to which genes contribute on a population level. Here's one review - https://academic.oup.com/schizophreniabulletin/article/43/4/788/2549005 https://academic.oup.com/schizophreniabulletin/article/43/4/... So you're right in asserting that schizophrenia likely isn't one clearly delineated disorder, but this is less due to an unclear 'medical definition', and more due to the fact that it's not entirely endophenotypic. It has sociogenic and psychogenic elements too - as do ALL psychological disorders. We diagnose from symptoms, but symptoms too are culturally mediated. We can never have a simple 'medical definition' of schizophrenia, because it's not only genetic, or only environmental, or only behavioural. It exists on the line between the creation and performance of personhood, and the biological mechanisms that make that possible. Put another way - if schizophrenics behaved 'normally' we wouldn't have a disorder at all. We deduce an internal experience of suffering, based on what they tell us of their inner experience (delusions and hallucinations), and the ways in which their behaviour departs from normative. We see a disease course, because many patients also have physical symptoms over the life course (like catatonia), although this is complicated by the brain damage caused by long term use of antipsychotics. A disorder of perception, selfhood and behaviour isn't reducible to a biological mechanism gone wrong - any more than joining a cult, following an extremist belief, or committing an act of terrorism would be. Those behaviours too could be said to have a genetic component - in so far as there are measurable aspects of impulsivity, neuroticism etc that can be used to explain them. But they're clearly not a disease in the conventional sense of the word.