Atopy

Genetic tendency to develop classic allergic diseases.

A hereditary allergic reaction.

Hypersensitivity to protein or non-protein substances, exposure to which produces asthmatic or other symptoms. The hypersensitivity of atopy is usually considered to be of genetic origin (allergy).

Allergy to which one has an inherited tendency.

A genetically determined allergic or hypersensitive response.

A form of allergy in which the hypersensitivity reaction may be distant from the region of contact with the substance (atopen) responsible. For example, a substance that is swallowed may give rise to a form of eczema, called atopic dermatitis.

Atopy, meaning out of place, is a form of hypersensitivity characterised — amongst other features — by a familial tendency. It is due to the propensity of the affected individual to produce large amounts of reagin antibodies, which stick to mast cells in the mucosa, so that when the antigen is inhaled, histamine is released from the mast cell. Atopy is the condition responsible for asthma and hay fever. It is estimated that 10 per cent of the human race are subject to atopy.

A type I hypersensitivity or allergic reaction for which there is a genetic predisposition. It differs from normal hypersensitivity reactions to allergens that are not genetically determined. The basis for the predisposition lies in the histocompatibility genes. The child of two parents with atopic allergy has a 75% chance of developing similar symptoms; if one parent is affected, the child has a 50% chance of developing atopy. Hay fever and asthma are two of the most commonly inherited allergies; contact dermatitis and gastrointestinal reactions also may be inherited. As with all type I hypersensitivity reactions, IgE is the primary antibody involved. Atopy is often associated with asthma.

Atopy refers to a predisposition in individuals to experience various allergic reactions. Atopic individuals have a heightened likelihood of developing one or more allergic disorders, including asthma, eczema, urticaria (nettle rash), and allergic rhinitis (commonly known as hay fever). This predisposition makes them more susceptible to these specific allergic conditions.

The exact mechanism behind the predisposition to atopy remains uncertain; however, it appears that atopy has a familial tendency. It tends to run in families, suggesting a genetic component in the development of this predisposition to allergic reactions.