What is Atopy?
Atopy is a genetic predisposition to develop allergic diseases such as allergic rhinitis, asthma, and atopic dermatitis (eczema), characterized by heightened immune responses to common environmental allergens, especially inhaled and food allergens, and the production of elevated levels of IgE antibodies. 1
Definition and Mechanism
Atopy refers to the inherited tendency to produce IgE antibodies in response to environmental antigens that are typically harmless to non-atopic individuals. This genetic predisposition is characterized by:
- A genetic disposition to develop allergic reactions and produce elevated levels of IgE upon exposure to environmental antigens, particularly inhaled or ingested allergens 1
- The tendency to manifest the "trinity" of classic allergic diseases: atopic dermatitis, allergic rhinitis, and asthma 2
- An immunologic aberration primarily driven by Th2 immune responses, coupled with skin barrier dysfunction in the case of atopic dermatitis 3
Genetic Basis
The inheritance pattern of atopy is complex and involves multiple genes:
- Family history is a strong predictor - children with two atopic parents have an 80% chance of developing atopic disease compared to 40% with one atopic parent and 10% with no atopic parents 1
- Genome-wide studies have identified associations between atopy and markers on more than 14 pairs of chromosomes (1,2,3,5,6,7,9,11,12,13,14,16,17,19) 1
- Different genes regulate total serum IgE levels versus specific IgE production 4
Clinical Manifestations
Atopy typically manifests as one or more of the following conditions:
- Atopic dermatitis (eczema): Often the first manifestation of the "atopic march," with onset in 60% of cases in the first year of life and 90% by age 5 3
- Allergic rhinitis: A symptomatic IgE-driven inflammation of the nasal mucosa resulting from allergen exposure in sensitized individuals 1
- Asthma: Children with food allergy have 4 times higher odds of having asthma 1
The Atopic March
The "allergic march" describes the progression of atopic conditions:
- Typically begins with atopic dermatitis in early infancy
- Progresses to allergic rhinitis, asthma, and food allergies as the child ages 1
- This progression has been observed in several birth cohorts 1
Prevalence and Risk Factors
Atopy is increasingly common worldwide:
- Seasonal allergic rhinitis (hay fever) affects approximately 10-20% of the population 1
- Food allergies affect an estimated 8% of children in the US 1
- Boys outnumber girls with allergic rhinitis in childhood, but the ratio becomes equal in adulthood 1
Risk factors for developing atopic disease include:
- Parental history of atopy (bilateral family history typically leads to earlier symptom development) 1
- Early exposure to environmental allergens during critical developmental periods 1
- Environmental factors such as pollution and tobacco smoke exposure 1
Diagnosis
Atopy is diagnosed through:
- Clinical history of allergic symptoms
- Elevated total serum IgE levels
- Positive skin prick tests or specific IgE to common allergens
- Increased peripheral blood eosinophils 4
Non-Allergic Forms of Atopy
It's important to note that some patients exhibit "intrinsic" or "non-allergic" forms of atopic diseases:
- These patients have normal IgE levels despite clinical manifestations of atopic diseases 5
- The mechanisms contributing to these non-allergic forms have been the subject of intensive research 5
Clinical Implications
Understanding a patient's atopic status has important implications:
- Atopic individuals are at higher risk for multiple allergic conditions
- Early identification may allow for preventive interventions
- The presence of asthma is a moderating factor in severe allergic reactions 1
- Atopic dermatitis carries a higher risk of bacterial skin infections (primarily Staphylococcus aureus) 3
Atopy represents a complex interplay between genetic predisposition and environmental exposures that ultimately determines whether clinical allergic disease will manifest or remain suppressed.