Endotype

An endotype is a subtype of a condition, which is defined by a distinct functional or pathobiological mechanism. This is distinct from a phenotype, which is any observable characteristic or trait of a disease, such as morphology, development, biochemical or physiological properties, or behavior, without any implication of a mechanism. It is envisaged that patients with a specific endotype present themselves within phenotypic clusters of diseases.

One example is asthma, which is considered to be a syndrome, consisting of a series of endotypes.^[1] This is related to the concept of disease entity

Disease entity

The main concept in nosology is the disease entity. Normally there are two ways to define a disease entity: Manifestational criteria and Causal criteria.^[2]

• Manifestational criteria. They are a set of criteria based in signs, symptoms and laboratory findings that define a disease. They define the disease by its symptoms and medical findings.
• Causal criteria are a causal chain of events that define the disease describing how it develops. They describe the disease by its etiology

Following Fred Gifford,^[3] these criterias lead to view any disease entity in three different forms:^[4]

• Disease as symptoms: The disease is defined by the symptoms and signs that produce. In fact, it can be said that the disease is the collection of them. It is the classical way to define a disease or condition.
• Disease as state: The disease is not defined by a set of symptoms, but by the underlying state of the body, including pathological tissues, abnormal cells, and any other general medical findings. This kind of definition allow the researchers to speak about silent diseases, which cannot be considered as such by the previous definition. Proponents of this kind of entities are for example Rudolph Virchow.
• Disease as a process: In the 20th century, a third concept of disease has appeared, based in the works of Caroline Whitbeck in 1977. She proposed that a disease would be defined by the clinical course of a set of untreated patients. She also argues that diseases are complex processes of which both clinical and underlying patho-physiological manifestations are proper parts (as contrasted with effects)

Following again F. Gifford, in fact each of the previous definitions can include the etiology or can be etiology agnostic. Other authors simply continue with the classification previous Whitbeck, leaving just three kind of definitions (clinical, pathological and etiological)^[5]

It is important to remark that a real world definition is normally an hybrid between these previous kinds, and an endotype should use all three of descriptors, including etiology, to guarantee specificity.

See also

• heterogeneous condition

Notes

1. Lötvall J, Akdis CA, Bacharier LB, Bjermer L, Casale TB, Custovic A, Lemanske RF Jr, Wardlaw AJ, Wenzel SE, Greenberger PA. Asthma endotypes: A new approach to classification of disease entities within the asthma syndrome. J Allergy Clin Immunol. 2011 Feb;127(2):355-60.
2. Victor J. Schoenbach, Phenomenon of disease, 2000
3. Peter Hucklenbroich, Disease Entity” as the Key Theoretical Concept of Medicine, Journal of Medicine and Philosophy, Volume 39, Issue 6, Pp. 609-633.
4. Fred Gifford (2011). Philosophy of Medicine. Elsevier.
5. Caroline Whitbeck, Causation in medicine: The disease entity model, Philosophy of science 44, 1977

References

• Anderson, GP (20 September 2008). "Endotyping asthma: new insights into key pathogenic mechanisms in a complex, heterogeneous disease". Lancet 372 (9643): 1107–19. doi:10.1016/s0140-6736(08)61452-x.