Hub Diseases in the DDN
To further characterize the DDN, we applied different network statistics to identify disease nodes necessary for the cohesiveness of the network. Such nodes are also commonly referred to as hub nodes (see Material and Methods). We used a betweenness centrality measure to identify hub nodes, which are represented in the DDN by larger nodes (Figure 2). We identified many hub nodes in different disease classes across the DDN; the highest number were in endocrine disorders and included hypothyroidism, type 1 diabetes, and type 2 diabetes (Figure 2). Other main hub nodes that we observed in the DDN were psoriasis, morbid obesity, multiple sclerosis, rheumatoid arthritis, coronary atherosclerosis, and chronic kidney disease.