Further understanding human disease genes by comparing with housekeeping genes and other genes.

Several studies have compared various features of heritable disease genes with other so called non-disease genes, but they have yielded some conflicting results. A potential problem in those studies is that the non-disease genes contained a large number of essential genes--genes which are indispensable for humans to survive and reproduce. Since a functional disruption of an essential gene has fatal consequences, it's more reasonable to regard essential genes as extremely severe "disease" genes. Here we perform a comparative study on the features of human essential, disease, and other genes. In the absence of a set of well defined human essential genes, we consider a set of 1,789 ubiquitously expressed human genes (UEHGs), also known as housekeeping genes, as an approximation. We demonstrate that UEHGs are very likely to contain a large proportion of essential genes. We show that the UEHGs, disease genes and other genes are different in their evolutionary conservation rates, DNA coding lengths, gene functions, etc. Our findings systematically confirm that disease genes have an intermediate essentiality which is less than housekeeping genes but greater than other human genes. The human genome may contain thousands of essential genes having features which differ significantly from disease and other genes. We propose to classify them as a unique group for comparisons of disease genes with non-disease genes. This new way of classification and comparison enables us to have a clearer understanding of disease genes.