Heterogeneous condition
A medical condition is termed heterogeneous, or a heterogeneous disease, if it has several etiologies (root causes); as opposed to homogeneous conditions, which have the same root cause for all patients in a given group. Examples of heterogeneous conditions are hepatitis and diabetes. Heterogeneity is not unusual, as medical conditions are usually defined pathologically (i.e. based on the state of the patient), as in "liver inflammation", or clinically (i.e. based on the apparent symptoms of the patient), as in "excessive urination", rather than etiologically (i.e. based on the underlying cause of the symptoms). Heterogeneous conditions are often divided into endotypes based on etiology. Where necessary to determine appropriate treatment differential diagnosis procedures are employed. 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. This is