In my line of work, about once a year, I encounter a patient with an unclassifiable disease, or Syndrome X. Generally, these are cases of congenital neurological defects, due to subtle genetic or chromosomal abnormalities, which have failed to find a place in the WHO (World Health Organisation) classification of diseases. A purist would say that it is impossible to have a single case of a syndrome, yet dictionaries allow the word to mean both a concurrent and recurrent clinical picture, so Syndrome X triumphs as a tentative diagnosis.

The prestigious scientific journal Nature has recently highlighted the true extent of the problem.