Authors' Reply

Abstract

To the Editor: In the letter to the editor, Marzuillo et al questioned our categorization of atopic eczema as a symptom of cow's-milk protein allergy (CMPA) (1). Rather, Marzuillo et al suggested that eczema is the cause of sensitization and CMPA, and that this may alter the management of affected children. We thank the authors for highlighting this complex relation and for creating an opportunity for clarification. Atopic dermatitis is a complex genetic disease influenced by many gene–gene and gene–environment interactions (2). Genetic effects appear particularly important for early-onset eczema as indicated by the high concordance in monocygotic compared with dizygotic twins and the high prevalence of mutations in the filaggrin (FLG) gene, which encodes a key protein involved in epidermal differentiation. Loss-of-function FLG mutations lead to a disturbed epidermal-barrier function and are the strongest risk factors for early-onset and persistent eczema with allergic sensitization, and later, asthma (3,4). Interestingly, eczema without sensitization (intrinsic eczema) does not appear to be associated with FLG mutations (3). Therefore, the association between early-onset eczema and the presence of food-specific immunoglobulin E may be explained by the genetic factors. We agree that the disorders in the skin barrier function associated with atopic dermatitis may facilitate sensitization via skin in predisposed infants; however, subjects sensitized to certain food allergens do not always show clinical symptoms when exposed to these foods (5). Furthermore, a high proportion of infants with symptomatic CMPA proved by a double-blind food challenge tested negative against specific immunoglobulin E (6). It is, in fact, clear that the infants with CMPA and eczema experienced increased skin inflammation when exposed to CMP and that their eczema improved or sometimes even resolved when dairy products were eliminated from the diet. As such, even if early-onset atopic eczema was not a symptom of CMPA in these children, but rather a genetically linked disorder, eliminating cow's milk from the diet was beneficial regardless of the sensitization status. These findings may have implications for primary or secondary prevention, which was not the topic of our position paper.