Rosacea Phenotype Distinction Between Subtypes

[Guide]

The ROSCO panel has changed the direction of classifying rosacea from subtypes to phenotypes. 

What is the difference between a phenotype based treatment vs a subtype based treatment?

Genetics

We have to begin with Genotype which "is the part (DNA sequence) of the genetic makeup of a cell, and therefore of an organism or individual, which determines a specific characteristic (phenotype) of that cell/organism/individual. Genotype is one of three factors that determine phenotype, the other two being inherited epigenetic factors, and non-inherited environmental factors." Wikipedia

Genotype-phenotype distinction

"The genotype–phenotype distinction is drawn in genetics. "Genotype" is an organism's full hereditary information. "Phenotype" is an organism's actual observed properties, such as morphology, development, or behavior." Wikipedia

A phenotype (from Greek phainein, meaning "to show", and typos, meaning "type") is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, phenology, behavior, and products of behavior (such as a bird's nest). Wikipedia

Watch this short whiteboard animation on the difference between genotype and phenotype:

Phenotype and Subtype in Medicine

Phenotype

A phenotype in medicine is "the observable properties of an organism that are produced by the interaction of the genotype and the environment." Merriam Webster Medical Dictionary

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." Wikipedia

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.

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." Wikipedia

Subtype 

A subtype in medicine is "a type that is subordinate to or included in another type <the blood group subtypes> <subtypes of a disease>." Merriam Webster Medical Dictionary

When the NRS 'expert' committee in 2002 began the classification of rosacea into subtypes, they did this based upon good motive. As one paper on this subject put it, "Broadly construed, disease subtyping is the task of identifying subpopulations of similar patients that can guide treatment decisions for a given individual. (When the subtypes have been established to be causally associated with the underlying mechanism, these are also called endotypes) Boland and colleagues describe the concept of a “vero-type” (the Latin word vero means “true”) to represent the true population of similar patients for treatment purposes. What constitutes these vero-types and how they should be discovered remains an open question. An active and growing body of work has explored different approaches for identifying homogeneous patient subgroups ranging from qualitative—based on clinical observations alone—to quantitative models that integrate mea- surements from diverse high-throughput biotechnologies." [1]

"Traditionally, disease subtyping research has been conducted as a by-product of clinical experience, wherein a clinician noticed the presence of patterns or groups of outlier patients and performed a more thorough (retrospective or prospective) study to confirm their existence." [1]

Subtype Related to Phenotype in Health Records

According to the author of the above referenced paper it appears that subtyping is related to 'Electronic Health Records and Phenotyping' and states, "Thus, much research has focused on developing new algorithms for annotating patient records with this information; in the literature, this task of extracting various clinical attributes for each individual is referred to as phenotyping....It is important to remember that phenotyping facilitates cleaner, but still broad, categories of disease....Thus, recent efforts have built on phenotyping work to move away from analysis of broad disease categories and instead provide more descriptive definitions of the disease over time."

Why is the phenotype classification superior to the subtype classification?  Answer. 

End Notes 

[1] AI and Health, Daniel B. Neill, H.J. Heinz III College, Carnegie Mellon University