Figure 1.

Causal structure of two complex diseases that have a clinically relevant mechanistic link. Different configurations of disease mechanisms can give rise to subtypes of disease (patients 1 and 2 share diagnosis A), or to diseases that have different clinical presentations, warranting unique diagnoses (patient 3 has diagnosis B). This causal structure has important therapeutic implications. For example, drug 1 would fail to illicit a therapeutic response for patient 2, but could be repurposed to treat patients with diagnosis B (patient 3). Thus, disease mechanism 1 provides a clinically relevant causal link between diagnoses A and B. Observed variables are in colored boxes.