Colleagues in our Computer Science department are developing a tool which identifies genes and medical terms taken from MeSH headings and its hierarchy (category C). I suppose that this in some way could be described as identifying co-morbidities and the responsible genes, but there are other things that they're also trying to solve.

I suggested that they also try to link the disease terms to symptoms whether they be external (eg, skin rash), invasive (eg, red blood cell count) or clinical (eg, results of a culture). However, no one present knew of a digital database linking symptoms to MeSH disease headings (category C), or anything similar.

Thus, we'd be grateful for any pointers or advice on this topic.

Not exactly a database solution, but a set of terminologies related to clinical symptoms / clinical procedures / classification of diseases are routinely used in biomedical informatics projects like the one you explained.

• International Classification of Disease (ICD) codes, current release is ICD-10
  
• Systematized Nomenclature of Medicine--Clinical Terms (SNOMED-CT)
  
• Current Procedural Terminology (CPT) codes

These terminologies were already mapped or can be mapped to MeSH terms.

See manuscript describing mapping of SNOMED-CT to MeSH here and ICD-9 to MeSH here.

You might also take a look at the Unified Medical Language System here, which includes MeSH. Often it also includes additional terms that are not found in MeSH.

Depending on your phenotypes, the Human Phenotype Ontology Website here may be useful.

Thanks for this question (similar to this other linked thread). Please visit this post for one possible way to go ahead with an open, distributed database of diseases X symptoms. Collaborators welcome!