It has been suggested that gene-environmental interactions play crucial roles in the development of allergy, especially in early life. Analysis of twin cases may provide novel insights into the pathogenesis and pathophysiology of allergy. Though several studies have indicated the importance of a genetic contribution to the expression of allergic diseases based on twin analyses, very few data are available regarding twins with Food Protein-Induced Gastrointestinal Syndrome (FPIGS). Two pairs of

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... dentical and fraternal twins with FPIGS are presented. Case Summary: The twins were born with no abnormalities and fed breast milk and supplemental formula. The identical twins developed vomiting and bloody stool simultaneously. The fraternal twins developed prolonged vomiting and loose stools at different times. Since their symptoms disappeared with when formula feeding was stopped, the symptoms were thought to indicate the presence of an allergy to cow's milk. The clinical symptoms and laboratory findings of the four patients were highly suggestive of FPIGS. The identical and fraternal twins showed very similar symptoms, including their onset and clinical courses. However, a substantial clinical disparity existed in the clinical features of the two pairs of twins. Discussion: Comparisons of the twins' similarities and disparities suggest a profound genetic effect on the patients' clinical features, along with individual environmental factors. The prevalence of FPIGS is increasing, and it is now a major topic of public concern in Japan. Further accumulation of data on twins with FPIGS is needed to clarify the genetic contributions to this disease.