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Diseases viewed as perturbed states of the molecular system
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In KEGG, diseases are viewed as perturbed states of the molecular system, and drugs as perturbants to the molecular system. Different types of diseases, including single-gene (monogenic) diseases, multifactorial diseases, and infectious diseases, are all treated in a unified manner as follows.
molecular network
Our knowledge on perturbed molecular networks has been captured and represented as disease pathway maps in the KEGG PATHWAY database (see, for example, the disease pathway map of chronic myeloid leukemia hsa05220). The KEGG DISEASE database is a collection of disease entries capturing knowledge on genetic and environmental perturbations. Each disease entry is identified by the H number and contains a list of known genetic factors (disease genes), environmental factors, diagnostic markers, and therapeutic drugs (see, for example, the disease entry of chronic myeloid leukemia H00004). Diseases with known genetic factors and infectious diseases with known pathogen genomes are being organized in KEGG DISEASE.

Disease Pathway Maps and Disease Entries

The Human Diseases category of the KEGG PATHWAY database is a collection of perturbed molecular networks. It contains multifactorial diseases such as cancers, immune system diseases, neurodegenerative diseases, cardiovascular diseases, and metabolic diseases where known disease genes (genetic perturbants) are marked in red. It also contains some infectious diseases where interacting molecular networks of both pathogens and humans are depicted.

The KEGG DISEASE entry only indicates membership information, i.e., association of genes and molecules to diseases, but may reflect the underlying molecular network. For single-gene diseases, perturbed pathway maps are not drawn, but causative genes are mapped to normal pathway maps through disease entries (see, for example, the disease entry of congenital disorders of glycosylation type I H00118 and the normal pathway map of N-glycan biosynthesis hsa00510).

There are a number of disease databases available, but they are mostly descriptive databases for humans to read and understand. Disease information in KEGG are in more computable forms, pathway maps and gene/molecule lists, enabling the analysis of molecular networks by integrating with different datasets, especially large-scale molecular datasets generated by sequencing and other high-throughput experimental technologies.

Disease/Drug Mapping

All known disease genes accumulated in KEGG DISEASE and all known drug targets stored in KEGG DRUG are integrated in the KEGG PATHWAY and BRITE databases. This is called disease/drug mapping and the resulting pathway maps and BRITE hierarchy files are identified by the five-letter organism code "hsadd" and the extension code "_dd", respectively.

toll-like For example, hsadd04620 shown right represents disease/drug mapping of toll-like receptor signaling pathway with the coloring convention as follows:
  • When the gene is associated with a disease, it is marked in pink.
  • When the gene (product) is a drug target, it is marked in light blue.
  • When the gene is both a disease gene and a drug target, its coloring is split into pink and light blue.
The disease/drug mapping is precomputed in the daily KEGG database update procedure, and each map or BRITE hierarchy can be selected from the organisms selection menu. For the disease/drug pathway maps the following list may also be used.
Disease genes and drug targets in KEGG pathways

Disease Classification

Human Organ Systems and Cells

Attempts are also being made to organize higher-level information as part of the BRITE database.

Last updated: July 1, 2016
KEGG GenomeNet Kanehisa Laboratories