Interesting Study Related to Cognitive Decline from Schizophrenia

 This study assessed whether cognitive decline from Schizophrenia has a genetic component. 

Schizophrenia polygenic risk predicts general cognitive deficit, but not cognitive decline in healthy older adults

In the early years of psychiatry, Schizophrenia was called "Dementia Praecox," a term coined by Emil Kraepelin, that described the deterioration of cognition associated with schizophrenia more so than the symptoms we normally associate with the disorder. From Wiki:

Dementia praecox (a "premature dementia" or "precocious madness") is a disused psychiatric diagnosis that originally designated a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood.

This term is no longer used, but the concept behind it is still accepted, that there is a progressive dementia among schizophrenic patients. The idea behind this study is that, assuming the polygenic model of schizophrenia holds true, if someone is not schizophrenic, but has a high polygenic score for schizophrenia (has a lot of the identified variants), then one might expect them to have some cognitive decline. That was not the case, as the study points out:

These results do not support the neo-Kraepelinian notion of schizophrenia as a genetically determined progressively deteriorating brain disease.

I think what this suggests is that schizophrenia, itself, is the cause of the cognitive deterioration, rather than the other way around.  Moreover, it challenges the polygenic model of schizophrenia and the idea of a "continuum" related to the number of susceptibility genetic variants, as Robert Plomin suggested in the book, "Blueprint.