Analysis of human disease genes in the context of gene essentiality.

The characteristics of human disease genes were investigated through a comparative analysis with mouse mutant phenotype data. Mouse orthologs with mutations that resulted in discernible phenotypes were separated from mutations with no phenotypic defect, listing 'phenotype' and 'no phenotype' genes. First, we showed that phenotype genes are more likely to be disease genes compared to no phenotype genes. Phenotype genes were further divided into 'embryonic lethal', 'postnatal lethal', and 'non-lethal phenotype' groups. Interestingly, embryonic lethal genes, the most essential genes in mouse, were less likely to be disease genes than postnatal lethal genes. These findings indicate that some extremely essential genes are less likely to be disease genes, although human disease genes tend to display characteristics of essential genes. We also showed that, in lethal groups, non-disease genes tend to evolve slower than disease genes indicating a strong purifying selection on non-disease genes in this group. In addition, phenotype and no phenotype groups showed differing types of disease mutations. Disease genes in the no phenotype group displayed a higher frequency of regulatory mutations while those in the phenotype group had more frequent coding mutations, indicating that the types of disease mutations vary depending on gene essentiality. Furthermore, missense disease mutations in no phenotype genes were found to be more radical amino acid substitutions than those in phenotype genes.