Clinical spectrum of food allergy in children in Australia and South-East Asia: identification and targets for treatment.

The prevalence of atopic diseases is increasing worldwide for reasons that are not clear. Food allergies are the earliest manifestations of atopy. This review defines the foods most commonly involved in allergic reactions and identifies an emerging group of syndromes in which food allergy is involved. A study of the frequency of food allergies in Australia and South-East Asia has recently shown that egg, cow's milk and peanut are the most common food allergens in Australia, but there were divergent results from different regions of South-East Asia. It is not clear whether the differences in reactivity to foods are due to genetic or cultural factors, but the findings raise the possibility that genetic susceptibility to food allergy may operate at the T-cell level modulated by the major histocompatibility complex. The Melbourne Milk Allergy Study defined a wide range of clinical symptoms and syndromes that could be reproduced by dietary challenge. A subsequent analysis of the infants with hypersensitivity to cow's milk and other multiple food proteins identified a new syndrome, multiple food protein intolerance of infancy. Food challenges demonstrated reactions developing slowly days after commencement of low-allergen soy formula or extensively hydrolysed formula. Follow-up at the age of 3 years showed that most children with this disorder tolerated most foods apart from cow's milk, egg and peanut. Atopic dermatitis affects about 18% of infants in the first 2 years of life. In a community-based study we have shown a very strong association (RR 3.5) between atopic dermatitis and infants with immunoglobulin E allergy to cow's milk, egg or peanut. Family studies on these infants have shown a link between atopic dermatitis and the genomic region 5q31 adjacent to the interleukin-4 gene cluster. Infantile colic (distress) affects 15-40% of infants in the first 4 months of life. Many theories of causation have been proposed, but a study from our centre showed that dietary modification, particularly that of breastfeeding mothers whose infants present with colic before the age of 6 weeks, alleviated symptoms. Colic associated with vomiting has been attributed to gastro-oesophageal reflux (GOR). This has been considered primarily a motility disorder, but a secondary form resulting from food protein intolerance has been described recently. We have also recently identified a group of infants with distressed behaviour attributed to GOR who have failed to respond to H2-receptor antagonists, prokinetic agents and multiple formula changes. Symptoms resolved on commencement of an elemental amino acid-based formula. In two-thirds of the patients, symptoms relapsed when challenged with low-allergen soy formula or extensively hydrolysed formula. We propose that a period of food protein intolerance is a part of the normal development of the immune system as it encounters common dietary proteins in infancy and early childhood. Future targets for research are development of appropriate dietary and management strategies for these entities and identification of genetic markers for these disorders.