Anaphylaxis caused by mustard in children: A case report from Japan

Despite reports in Western countries, mustard allergy is rarely acknowledged in Japan. Here, we present the case of a 4-year-old girl without previous allergies who developed anaphylaxis after eating a hot dog containing mustard and required intramuscular epinephrine administration. ImmunoCAP testing revealed mustard-specific immunoglobulin E (6.72 kUA/L), and the skin prick test was strongly positive to yellow mustard, oriental mustard, and processed mustard products. Oral food challenge (OFC) with 10 mg mustard (approximately 0.4 mg mustard protein) provoked vomiting. Therefore, she was diagnosed with mustard allergy. Two-dimensional western blot analysis and mass spectrometry led to the identification of 12 proteins from 10 immunoglobulin E (IgE)-binding spots; however, none corresponded to known mustard allergens (Sin a 1–4). Notably, spot 7 exhibited significant IgE-binding but remained unidentified, suggesting potential novel allergens. This is the first documented case of mustard allergy in Japan verified with OFC, highlighting both the risk of severe reactions at minimal doses and the importance of OFC for diagnosis. Further studies using recombinant allergens are warranted to validate the clinical relevance of the newly identified proteins in the present case.