Formally relatedness is revealed in classification of illness into categories of 'like things'. That practice is called 'nosology' the discipline of naming illnesses.
Most of us are familiar with zoological and botanical classifications wherein organisms are placed into categories based on shared genetic and evolutionary history. Such classifications have biological coherence and make possible comparative studies--biologists consequently know under what circumstances where the biology of a bacteria, a bass or badger can be used as a reasonable model for human biology (and they all could be for different types of study).
Historically classification of mental illness has been based on patterns of obvious clinical symptoms. Under that consideration a mental illness is seen as belonging to anxiety disorders, mood disorders, psychotic disorders, impulse disorders and personality disorders, with a couple others such as somatoform, sexual disorders, and faking disorders etc thrown in to fill out the corners.
Until very recently classifications of mental illness were made by clinicians with very little knowledge of the neurological mechanisms that cause mental illness. That's particularly true at the molecular/cellular level considered in this study. The lack of knowing underlying causes forced the field to focus in on symptoms and promoted some pretty interesting early conceptualizations (ego, id, narcissistic injury) and very elevated erudition about what are basically imaginary heuristic constructs.
Because this study links neuro-biological features of calcium channels across existing categories of mental illness it underscores how the traditional classification is not always very reflective of the biological foundations of mental illness.
This study is another step forward for those arguing for classifications of mental illness that may make sense of mental disorders at molecular as well as clinical levels. It is one of the growing number of studies in molecular and cellular neurobiology that point to the need to reconsider how clinicians split or lump illnesses and thereby choose appropriate treatments for illnesses whose biological relatedness may be quite mistaken.
Focusing on the importance of 'now they know calcium channels in cell membranes need attention' rather misses a probably more important point : Symptoms-based classifications of mental illness are mistaken, and that may confuse rather than clarify the practice of psychiatric medicine.
But that's my opinion and I'm just a lay-person with a bit of understanding of the importance of systematics.
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