The rendering of human phenotype and rare diseases in ICD-11.

ICD-11 (International Classification of Diseases, 11th Revision) is the next major revision of the ICD by the World Health Organization (WHO). ICD-11 differs dramatically from historical versions, as it is based on an underlying semantic network of terms and meaning, called the Foundation. To function as a mutually exclusive and exhaustive statistical classification, ICD-11 creates derivative linearizations from the network that is a monohierarchy with residual categories such as Not Elsewhere Classified. ICD-11 also introduces the widespread post-coordination of terms, which allows for highly expressive representation of detailed patient descriptions. Phenotyping features are included in many subchapters or the signs and symptoms chapter. Composite phenotype descriptions of specific presentations or syndromes can be represented though post-coordination. Rare diseases are well represented in the Foundation, though not all appear in the relatively shallow linearization hierarchies.