Asthma phenotyping and endotyping

Asthma phenotyping and endotyping
Diagram illustrating the different phenotypes and endotypes of asthma
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Asthma phenotyping and endotyping are approaches used to classify asthma into distinct subtypes based on observable characteristics (phenotypes) and underlying biological mechanisms (endotypes). This classification helps in understanding the heterogeneity of asthma and in tailoring personalized treatment strategies.

Overview

Asthma is a chronic inflammatory disease of the airways characterized by variable and recurring symptoms, airflow obstruction, and bronchospasm. Traditionally, asthma was considered a single disease entity, but it is now recognized as a syndrome with multiple phenotypes and endotypes.

Phenotypes

Phenotypes are observable characteristics of asthma that can be identified through clinical features, triggers, and responses to treatment. Common asthma phenotypes include:

• Allergic asthma: Characterized by a history of allergic reactions, elevated IgE levels, and positive skin prick tests.
• Non-allergic asthma: Occurs without an allergic component, often triggered by irritants such as smoke or pollution.
• Late-onset asthma: Develops in adulthood, often more severe and less responsive to standard treatments.
• Exercise-induced asthma: Triggered by physical activity, leading to bronchoconstriction during or after exercise.
• Aspirin-exacerbated respiratory disease (AERD): Asthma associated with nasal polyps and sensitivity to aspirin and other NSAIDs.

Endotypes

Endotypes are subtypes of asthma defined by distinct pathophysiological mechanisms. Identifying endotypes involves understanding the underlying biological processes, such as:

• T2-high asthma: Characterized by elevated levels of type 2 cytokines (IL-4, IL-5, IL-13), eosinophilia, and responsiveness to corticosteroids and biologics targeting IL-5 or IL-4/IL-13 pathways.
• T2-low asthma: Lacks the typical type 2 inflammation markers, often associated with neutrophilic inflammation and less responsive to corticosteroids.

Clinical Implications

Understanding asthma phenotypes and endotypes is crucial for personalized medicine. It allows for:

• Targeted therapies: Use of biologics such as monoclonal antibodies targeting specific cytokines or receptors.
• Improved diagnosis: More accurate identification of asthma subtypes can lead to better management strategies.
• Predictive outcomes: Understanding the endotype can help predict disease progression and response to treatment.

Research and Future Directions

Ongoing research aims to further refine asthma phenotyping and endotyping through:

• Biomarker discovery: Identifying new biomarkers for more precise classification.
• Genetic studies: Understanding the genetic basis of different asthma endotypes.
• Environmental factors: Investigating the role of environmental exposures in shaping asthma phenotypes.

Also see

• Asthma
• Chronic obstructive pulmonary disease
• Allergy
• Biologics in asthma treatment