DermO; an ontology for the description of dermatologic disease
© The Author(s). 2016
Received: 21 November 2015
Accepted: 3 June 2016
Published: 13 June 2016
There have been repeated initiatives to produce standard nosologies and terminologies for cutaneous disease, some dedicated to the domain and some part of bigger terminologies such as ICD-10. Recently, formally structured terminologies, ontologies, have been widely developed in many areas of biomedical research. Primarily, these address the aim of providing comprehensive working terminologies for domains of knowledge, but because of the knowledge contained in the relationships between terms they can also be used computationally for many purposes.
We have developed an ontology of cutaneous disease, constructed manually by domain experts. With more than 3000 terms, DermO represents the most comprehensive formal dermatological disease terminology available. The disease entities are categorized in 20 upper level terms, which use a variety of features such as anatomical location, heritability, affected cell or tissue type, or etiology, as the features for classification, in line with professional practice and nosology in dermatology. Available in OBO flatfile and OWL 2 formats, it is integrated semantically with other ontologies and terminologies describing diseases and phenotypes. We demonstrate the application of DermO to text mining the biomedical literature and in the creation of a network describing the phenotypic relationships between cutaneous diseases.
DermO is an ontology with broad coverage of the domain of dermatologic disease and we demonstrate here its utility for text mining and investigation of phenotypic relationships between dermatologic disorders. We envision that in the future it may be applied to the creation and mining of electronic health records, clinical training and basic research, as it supports automated inference and reasoning, and for the broader integration of skin disease information with that from other domains.
KeywordsDermatology Ontology Disease Dermatopathology
Estimation of the impact of skin disease on population morbidity and mortality has always been complicated by the nature of the terminologies used for recording disease incidence, prevalence and cause of death. However measured, it remains a highly significant social, economic and clinical burden. In the USA, collective prevalence estimates for skin disease are greater than those of obesity, hypertension and cancer . There have been repeated initiatives to generate structured terminologies of sufficient granularity to accurately capture skin disease diagnoses, but the available tools, such as ICD-10, remain blunt instruments in the face of the pressing need for precision phenotyping, and are unsuitable for many types of computation-based research. We have, with the close involvement of domain experts in dermatology, pathology, and genetics, consequently created a new ontology, DermO, for cutaneous disease.
There have been several previous initiatives to devise lexicons or structured comprehensive terminologies for the description of cutaneous disorders, for example the Dermatologischer Diagnosenkatalog . The most recent is the DermLex ontology [3, 4], created under the auspices of the American Academy of Dermatology, with the purpose of providing a definitive nomenclature for clinical dermatology . This terminology was merged with the British Association of Dermatologist’s BAD Index and is mapped to International Classification of Disease (ICD9-CM) codes. However, maintenance of DermLex was discontinued in 2009. This lexicon covered sporadic and inherited cutaneous disorders and consisted of 6104 terms including a nosology, classic signs, therapeutic procedures, and anatomical distributions. To date DermLex has been the most comprehensive tool for capturing dermatological disease information. The Human Disease Ontology (DO)  also contains an integumentary branch of 234 terms, with skin and adnexal diseases classified as skin, hair, and nail disease. Likewise, the Human Phenotype Ontology (HPO)  contains a branch of skin and adnexal phenotypes with terms focused on phenotypic manifestations of cutaneous disorders. Skin diseases are largely out of the scope of HPO, which primarily focuses on phenotypes and does not aim to cover the breadth of cutaneous conditions we envisage. Similarly, the DO’s coverage and organization of the integumentary branch is limited and may not entirely capture the breadth and diversity of cutaneous conditions required for the purposes of patient stratification, population analysis, cross-species comparisons, database query expansion and automated reasoning.
The current revision of ICD, ICD-11, will contain the most radical revision of dermatology terms since 1948 and so far around 2000 terms have been assigned to the dermatology chapter (XII) with 20 major subdivisions . ICD-11 is not currently finalized (June 2016) and uptake is expected to be gradual (for example the USA has only recently transitioned to ICD-10 for electronic health records as of 1.10.15) .
The other main resource for dermatological disease terms is SNOMED-CT. Whilst SNOMED contains more than 2000 terms related to cutaneous disease the coverage and structure of the terminology does not lend itself to detailed clinical description and having a relatively flat hierarchy does not permit the relationships between diseases to be used computationally in a useful way. (Discussed in ). An additional issue remains the licensing of SNOMED-CT by the International Health Terminology Standards Development Organization (IHTSDO) that precludes its free use in some countries.
The main applications for DermO are data capture and informatic analyses that only recently have become feasible using electronic health records, and semantic integration of disease information between species and across domains of knowledge; these analyses require a sufficiently rich structure, granularity, and coverage from the available terminologies. We have therefore created a new ontology from the scientific literature with the close involvement of domain experts in dermatology, pathology, and genetics, while explicitly maintaining interoperability with established ontologies and vocabularies in the biomedical domain, DermO is organized in a manner intuitive to dermatologists and dermatopathologists. The framework adopted for the development of DermO was based on that of the definitive clinical dermatology text, Dermatology by Bolognia et al. . The specific aim is to include all of the currently accepted primary and secondary skin diseases, including those caused by systemic disorders, external insult, and the genodermatoses. DermO was developed with the intention of creating a tool applicable to patient care, clinical training and basic research, as well as to support automated inference and reasoning. It can be used for patient stratification, genotype/phenotype studies, and for the broader integration of skin disease information with that from other domains, such as model organism phenotypes and pharmacogenomics for translational science. DermO is freely available on https://github.com/dermatology-ontology/dermatology.
DermO was constructed by domain experts using the framework of the most recent definitive text on Dermatology edited by Bolognia et al. . The approach taken was to produce a classification familiar to dermatologists, as the envisaged uses of DermO include both patient diagnostic annotations by clinicians and mining of electronic health records. The formalization of patient information provides a data resource that can be expanded to integrate historical and newly generated information from both human and mouse dermatology, and genetic studies.
The structure adopted for DermO is familiar both for diagnostic support and patient data recording purposes. Because of the inclusion of systemic and inherited diseases, DermO also includes diseases that would normally be found in other branches of a disease ontology, such as Mendelian monogenic syndromes, and for completeness we therefore use a degree of polyhierarchy and include genetic diseases (the genodermatoses) as well as systemic diseases. For the same reasons the ICD-11 topic advisory group adopted a similar approach .
The ontology was manually constructed using OBO-Edit  and the OWL2 version prepared using Protégé . Consistency was verified using the HermiT reasoner , which detected no inconsistencies and no unsatisfiable classes, mainly due to the absence of disjointness axioms in the ontology. The main ontology is available in both the OBO Flatfile format  and the Web Ontology Language (OWL) . DermO is housed in a Github repository and is made available via Bioportal (permanent URL: http://purl.bioontology.org/ontology/DERMO) , Aber-OWL (permanent URL: http://aber-owl.net/ontology/DERMO) and on the project’s website https://github.com/dermatology-ontology/dermatology.
Content, relations and mapping to other ontologies
Upper level classes of the DermO ontology
Anogenital non-venereal disease
Atrophy or disorder of dermal connective tissue
Disorder caused by infections, infestations stings or bites
Disorder due to physical agent
Disorder of hair or nails
Disorder of Langerhans cells or macrophages
Disorder of neoplasm of the skin
Disorders of subcutaneous fat
Metabolic or systemic disease
Papulosquamous or eczematous dermatosis
Pruritis, dysaesthesia or psychocutaneous disorder
Urticaria, erythema or purpura
Cross-ontology mapping of DermO classes
Number of cross-referenced classes
Human Phenotype Ontology
The majority of relations used to structure DermO are is-a relations. Where appropriate, the results-in and has-symptom relations are also used to indicate where a disease develops as a sequel to another or where a disease is characterized by specific manifestations that might also occur in isolation. This latter relationship might also be viewed as that between a disease and phenotype as discussed below.
Integration of the widest possible range of disease concepts into DermO brought with it challenges also seen in other phenotype and disease ontologies, such as DO and HPO which are dealt with in different ways, if indeed they are systematically addressed at all. The strategy we took was to allow multiple axes of classification, requiring polyhierarchy and resulting in a greatly increased richness. There are particular design considerations with the genodermatoses and etiologically predicated sub-types of disease. Our solutions and reasoning may be helpful to other developers of phenotypic and disease ontologies.
The definition of a genodermatosis varies between terminologies  but broadly refers to inherited genetic skin conditions, often part of phenotypically diverse syndromes, and including mono-, polygenic, and chromosomal lesions. Probably the most comprehensive recent attempt to classify these is from Feramisco et al. [24, 25] who produced a database of genodermatoses derived from OMIM. They used manually curated phenotype terms to define the skin phenotypes of these genodermatoses to generate a phenotypic map of these diseases in order to discover novel relationships. We included most of the genodermatoses captured by Feramisco et al. into DermO, and also have added those considered by other studies, leading to a total of 537 genodermatoses in DermO. Furthermore, we have included subtypes of genodermatoses in phenotypic series and variants that did not receive their own OMIM identifier as separate manifestations rather than adopting the strategy of collapsing all the variants into a broad disease. For example, hidradenitis suppurativa (DOID: 2280) includes three subtypes of a phenotypic series (OMIM: 142690, OMIM: 613736, OMIM: 613737), all of which have a distinct phenotype and genetic etiology (NCSTN, PSENN, and PSEN1 respectively). To facilitate studies of molecular mechanisms using DermO, such as classification in pathway analyses, patient population stratification, or identification of drugs for diseases in which each subtype may have different therapeutic indications, we separate the three sub-types of hidradenitis suppurativa into individual diseases. There are other cases where disease subtypes have no separate OMIM identifiers. For example, in the case of Darier-White disease (OMIM: 124200) we identify 11 subtypes. Only two are recognized in OMIM, “segmental” and “acral-hemorrhagic”, and neither have independent identifiers. No subtypes are listed for this disease in the genodermatosis database of Feramisco et al. We identify all of these as separate diseases in DermO so that their different etiology can be taken into account in data analysis.
Etiologically predicated disease subtypes
Parallel classification of diseases by etiology allows for discrimination between the actions of different agents, which, although leading to the same outcome, may do so by different pathogenetic mechanisms – often termed “phenocopy”. In cases where this is well established, such as psoriasis , we have created subclasses of diseases based on the etiologic (causative or exacerbating) agent, such as virus, bacterium, or physical trauma, with the aim of being able to capture potentially important information for patient stratification and genotype/phenotype association. Such disease classes then have subclass relationships to classes that structure dermatological diseases based on their etiology. For example, fungal skin disease (DERMO:00002246) is a parent of “psoriasis triggered by fungal infection” (DERMO:0000004) , which has as its second parent “psoriasis” (DERMO:0000124). This enables identification of all the fungal skin diseases (including psoriasis triggered by fungal infection), or, using the other parent, identifying all the inflammatory dermatoses.
Literature mining and network construction
Literature mining and construction of a phenotypic relatedness network for DermO classes was carried out as previously reported by us for the DO , and full methods may be found in this paper. In brief, the Aber-OWL: Pubmed infrastructure was used to semantically mine Medline abstracts. Aber-OWL: Pubmed (http://aber-owl.net/aber-owl/pubmed/) consists of an ontology repository, a reasoning infrastructure providing OWL-EL reasoning over the ontologies in the repository, a full text index of all Medline 2014 titles and abstracts as well as all Pubmed Central articles, and a search interface as described in Hoehndorf et al. . Documents were dealt with as a title and abstract and filtered by presence of at least one term from a phenotype ontology (MP or HPO) and one term from DermO. The resulting indexed corpus consisted of 781,000 documents.
Statistically significant co-occurrences of disease and phenotype terms were identified using Normalized Pointwise Mutual Information (NPMI)  with the aim of associating HPO and MPO classes with individual concepts from DermO.
Results and Discussion
Scope and structure of DermO
Diseases of the skin and its adnexa fall mainly into three major categories which are well recognized by dermatologists; disease originating in the skin (sporadically or in response to external insults) with mainly cutaneous manifestations (I), diseases of the skin resulting from systemic disease such as metabolic or endocrine disorders (II), and heritable or genetic disease where skin manifestations are part of a syndrome (III) and may either arise independently of other aspects of the syndrome, or as a secondary consequence. The nature of cutaneous diseases, as with other anatomically classified diseases, include hyperplastic, dysplastic, neoplastic, and degenerative disorders for example, but many disease entities include manifestations of several of these pathological processes. This complexity consequently provides problems in how to logically classify the diseases.
DermO aims to capture knowledge about the domain of human cutaneous disorders in the form of a directed acyclic graph. It does not contain information about devices, procedures, diagnostic measurements or patient management. The ontological definition of diseases as dispositions rooted in physical disorders, realized through pathological processes, as proposed by Scheuermann et al. , is consistent with the criteria used for inclusion in DermO and all are children of the root term “cutaneous disease”. However the distinction between “phenotypes” and “diseases” is less clear; an issue with most attempts to capture the clinical domain. For example “atopic dermatitis” (DERMO:0000122) occurs sporadically and in isolation, and is regarded as a cutaneous disease, but also occurs as part of more complex syndromes such as mental retardation, obesity, mandibular prognathism with eye and skin anomalies  (MOMES syndrome) (OMIM: 606772) and consequently is treated as a disease in DO (DOID:3310 “atopic dermatitis”) and a phenotype in HPO (HP:0000964 “atopic dermatitis”). We feel that in such cases the distinction between “disease” and “phenotype” is largely dependent on context and have consequently included all that may be regarded as clinical disease entities, as opposed to clinical phenotype observations, as part of DermO, with cross-references to other ontologies where they also occur.
The disease entities in DermO are categorized in 20 upper level terms which use a variety of features such as anatomical location, heritability, affected cell or tissue type or etiology, as the features for classification, in line with professional practice and nosology in dermatology (Fig. 1, Table 1). The maximal depth is 11, and the majority of axioms used to structure DermO use is-a relations. 1,330 terms are common to DermO and DO and 373 are common to HPO, 152 to the Mammalian Phenotype Ontology (MPO), 1509 to the Medical Subject Headings (MeSH) thesaurus , 1398 to the Unified Medical Language System (UMLS), 537 to ICD-10, and 1054 to DermLex. 1203 classes in DermO map to 2337 classes in SNOMED-CT (RF2 release; USA, September 2015) (see Table 2). About half the classes could not be mapped to any of the above terminologies (1773), while many were mapped to more than one terminology, indicating significant redundancy of classes within the set of ontologies we used.
Using DermO to mine the biomedical literature
There currently exists no high quality comprehensive phenotypic description of complex and common dermatological diseases. Using the approach we pioneered to harvest phenotypic descriptions of common disease from the scientific literature we have applied the same methodology using the coverage and resolution provided by DermO. The results of this analysis provide a rich resource of the associated phenotypes for dermatological diseases, including symptoms and co-morbidities. Using these descriptions to establish the phenotypic relatedness of the disease concepts in DermO we can generate a similarity network that provides insights into the mechanistic and pathobiological nature of these entities. It also a provides a novel and objective axis of classification, different to that traditionally used in dermatology, with the potential for providing novel insights into the pathobiology.
The text-mined phenotypes are now integrated into Phenomenet  which allows for exploration of existing mouse models using the richer phenotypic descriptions of the skin diseases we provide. This supports disease gene discovery, where the gene (s) underlying a disease in humans is (are) unknown, and translational research. Such descriptions have not previously been available for common and complex skin disease.
DermO was conceived as a formal ontology and structured terminology to describe human cutaneous diseases. DermO can be used as a tool in patient care, clinical training and basic research. The provision of disease relationships and groupings which have pathobiological and etiological significance based on phenotype makes DermO valuable for using automated inference and reasoning as well as in data mining applications, but we envisage wider applicability, from precision phenotyping of patients, through differential diagnosis, to the discovery of new physiological and pathophysiological pathways and integration of human and model organism phenotype data.
DermO can be used to extract data from patient electronic health records using text mining, or to translate existing variable-granularity coding such as ICD-10 to allow capture and standardization of patient/disease annotations. For example ICD-10 has 19 sub- types of bullous disorder including Not Otherwise Specified (NOS), whereas, excluding the bullous diseases of the newborn, DermO contains 84. Using the structure of the ontology patients may be grouped or split at different levels of granularity which will enable the fine-tuning of both Genome Wide Association Studies (GWAS) and Phenome Wide Association Studies (PheWAS) [37, 38] analysis. This will facilitate both the discovery of new genetic variation underlying skin diseases and the establishment of unexpected skin and other phenotypes associated with established genetic variants in and around genes identified as important through hypothesis-driven research. An additional advantage of this approach is the potential to identify other variation-associated predisposed phenotypes which might not have been noted previously, and which may shed light on the pathobiology of the disease through the introduction of novel and objective axes of classification by phenotype. In the future, we envision integrating DermO with the integumentary disease branch of the DO so that the deep and broad coverage of dermatological diseases we provide in DermO can be used in conjunction with other diseases within the DO. DermO, as with other open ontologies, is owned by the community that uses it and so we encourage users to participate in its development and improvement through the project website.
human disease ontology
genome-wide association studies
human phenotype ontology
- ICD-9, 10, 11:
international classification of disease versions 9, 10, and 11
medical subject headings
mammalian phenotype ontology
not otherwise specified
open biomedical ontologies
online mendelian inheritance in man
web ontology language
phenome-wide association studies
Paul N. Schofield
unified medical language system
The authors acknowledge National Institutes of Health Grants R21-AR063781 to JPS and SSD, and R01HG004838-03 supported PNS and GVG. We thank Prof. Jonathan Bard for helpful comments on the manuscript and Prof. Amanda Oakley, for the support of DermNet NZ.
Initial construction of the ontology was carried out by HMF and subsequently all authors contributed to its development. PNS lead the writing of the paper and all authors contributed. Mapping to other terminologies was done by RH, BSB, and GVG. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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