Which disorder's criterion A is met during a major mood episode?

In schizoaffective disorder, Criterion A is met during a major mood episode, which includes symptoms of a mood disorder such as major depressive episodes or manic episodes. The essential feature of schizoaffective disorder is the presence of both mood disorder symptoms and psychotic symptoms that occur concurrently. This duality ensures that the diagnosis aligns with the complexity of the individual's experience, where psychotic features are intertwined with the mood disturbances.

In contrast, the other disorders listed do not require the presence of mood episodes as a defining aspect. Brief psychotic disorder and schizophreniform disorder focus primarily on psychotic symptoms without the necessity of mood episodes for diagnosis. Meanwhile, psychotic disorder due to another medical condition pertains to psychotic symptoms arising as a direct consequence of a medical condition, which similarly does not involve mood episodes as an essential criterion.

This distinction reinforces the importance of the mood episodes in the diagnosis of schizoaffective disorder, making it unique among the options provided.