LAUSR

The vast majority of food allergies in children are caused by few foods, namely cow's milk, egg, wheat, soya, peanut, tree nuts, fish, and shellfish.1 However, as a practicing allergist, one needs to have an open mind as allergy can be caused by virtually any food. It is important to report rare allergies to increase awareness and support the diagnosis of new cases should this be suspected. Furthermore, with globalization and dissemination of cuisines around the world, knowledge about new foods and new allergens is very valuable. We report the case of a 5yearold boy of Nigerian descent with a history of immediateonset urticaria, periorbital angioedema, and vomiting after the ingestion of egusi melon seeds at the age of 6 months. He had a history of urticaria and vomiting on exposure to cow's milk at 3 months of age and reported similar reactions to coconut, peanut, almond, and hazelnut in the first year of life. He had a background of earlyonset atopic dermatitis, which was recently well managed with mild topical corticosteroids, mild seasonal allergic rhinitis, and viralinduced wheeze. There was a family history of atopy as the father had a history of asthma and allergic rhinitis. Cow's milk had since been successfully reintroduced into the diet, but he continued to avoid egusi seed, all nuts, and coconut, as well as sesame seed due to evidence of sensitization on blood testing. As egusi seed formed an important part of the family's diet, the family were keen to reintroduce egusi seed if possible, and cashew, coconut, or peanut were in second line of priority. Skin prick tests were performed in clinic and blood was collected for specific IgE testing and the basophil activation test (BAT). The BAT was performed to peanut to confirm the need for food challenge as part of an ongoing research study (Research Ethics Committee reference 10/H0802/44) and to egusi seeds to confirm the diagnosis, following parental consent and child's assent. The BAT was performed as previously described2,3 using a peanut extract prepared by ALKAbello and an inhouse prepared egusi seed extract alongside with negative (Roswell Park Memorial Institute (RPMI) 1640 Medium alone) and positive controls, namely antiIgE and Nformylmethionylleucylphenylalanine (fMLP)— for details on the methodology, see supplementary material. Briefly, dehulled egusi seeds were ground and homogenized in phosphatebuffered saline (PBS) for overnight cold extraction. Crude extract was then centrifuged and filtered using Whatman paper. Protein precipitation was performed using saturated ammonium sulfate until 80% saturation was reached. The resulting pellet was dissolved in ultrapure water then dialyzed in deionized water overnight at MWCO 3500. BCA assay was performed to determine total protein content of aqueous extract and an SDSPAGE was used to determine the presence and approximate size of proteins in the extract for use in the BAT. There were multiple bands from a molecular weight of ~10 kDa to ~130 kDa, the main one being at ~50 kDa. (Figure E1). The results of SPT and specific IgE are represented in Table 1. The BAT to peanut was positive, that is, above the optimal diagnostic cutoff (4.78% CD63+ Basophils) previously validated in our center, and the patient was therefore not referred for an oral food challenge, which the family was reassured about as they were anxious about the idea of exposing their child to peanut. The BAT to egusi seeds showed a dosedependent increase of the expression of CD63 on the surface of basophils with increasing concentration of egusi seed allergen extract with a peak of 73.71% net CD63+ basophils at 10,000 ng/ml (Figure 1). A similar doseresponse was also observed for the CD203c stimulation index. Basophil response to both antiIgE and fMLP controls were detectable, with 61.01% and 12.71% net CD63+ basophils, respectively. The combination of BAT, SPT, and the history confirms the diagnosis of egusi seed allergy. Strict avoidance of peanut, all tree nuts, coconut, sesame seed, and egusi seed was advised and a written emergency management plan was given along with emergency medication, consisting of 2 adrenaline autoinjectors and cetirizine. Egusi (Citrullus mucosospermus), sometimes referred to as egusi melon or egusi watermelon, is part of the Cucurbitacaeae family and is closely related to watermelon.4,5 It is found in the tropics, from West Africa through to Sudan. Although the flesh of the fruit is dry and bitter, the seeds can be dried and ground and are commonly used to thicken soups in West African cuisine.6 To our knowledge, this is the first documented case of egusi seed allergy. We were able to confirm the diagnosis suggested by the clinical history with detection of functional IgE to egusi seeds on SPT and the BAT. In cases of suspected allergy to exotic foods or rare allergens, modified skin prick testing using the implicated food may be the only test available to confirm the allergy. It should also be noted, that in our patient, the skin prick test diameters were initially quite small— despite a convincing history of reaction to egusi seeds— and then became larger at age 6 years, probably reflecting a more established immune allergic response and demonstrating the importance of a detailed clinical history and the benefit of repeated skin prick testing in children over time. A similar pattern was observed in other nuts and seeds, while in some cases, the specific IgE levels for the