In a complex disease, the expression of many genes can be significantly altered, leading to the appearance of a differentially expressed disease module. Some of these genes directly correspond to the disease phenotype, (i.e. driver genes), while others represent closely-related first-degree neighbours in gene interaction space. The remaining genes consist of further removed passenger genes, which are often not directly related to the original cause of the disease. For prognostic and diagnostic purposes, it is crucial to be able to separate the group of driver genes and their first-degree neighbours, (i.e. core module) from the general disease module.