Fuzzy disorder boundaries arguably reflect a diagnostic system that was largely constructed based on clinical observation and expert consensus. An alternative path forward is to look towards creating a bottom-up nosology based on biological research, such as the cross-disorder genomic results reviewed here. In line with research initiatives like RDoC (Insel & Cuthbert, 2009) and HiTOP (Kotov et al., 2017), future diagnostic manuals may describe alterations in dimensions of functioning, as opposed to discrete categories. Psychiatric genomics indicates that the majority of these dimensions are likely to be shared across the disorders, while fewer may be highly disorder specific. Future mechanistic and genomic modeling research can begin to inform how these dimensions map onto our current categories, an enterprise that has tangible clinical implications. For example, it is standard clinical practice to ask about family history of mental illness as this can inform the differential diagnoses under consideration. Consider a patient in the current framework who is diagnosed with SCZ and has a family history of BIP. A future diagnostic system might use convergent evidence across different levels of explanation
