### Description

This column shows the neighborhood of protein interactions surrounding the selected gene. The neighborhood is computed from a genome-wide protein-protein interaction network. The network connects genes if the proteins they encode have been detected to physically interact in high-throughput experiments.

The network distance listed in the column shows the number of interactions between a gene and the selected gene. For example, genes whose protein products have been detected to directly interact are listed with a network distance of one. Genes that share a direct interaction with a protein that also directly interacts with the selected gene are listed with a distance of 2. For example, if the protein of gene X interacts with the protein of gene Y (but not the protein of the selected gene), and Y's protein interacts with the selected gene, then gene X will have a distance of 2.

For protein-protein interactions in "complex" multi-protein associations, the distance 1.5 was used instead of 1.0 since it is not necessarily known that the two proteins are in direct contact.

Because the protein interaction network is highly connected (i.e. most genes are connected to one another by some distance), we limited the size of the neighborhood to contain only those genes within a pre-specified distance (2 by default).

### Example Protein-Interaction Network

Distance AB is 1 because proteins from genes A and B interact directly.
Distance AD is 2 because proteins from genes A and D interact indirectly through gene C protein.
Distance AA is 1 because the gene A protein is known to interact directly with itself.
Distance AE is 1.5 because proteins from genes A and E are involved in a "complex" interaction cluster but A and E are not known to directly interact.

### Credits

The interaction data were provided by the Human Protein Reference Database.