Abstract

Difficult-to-control asthma may be associated with continuous exposure to allergens, particularly professional ones, presence of comorbidities and lack of adherence to therapy. A component-resolved approach can provide an invaluable support to the diagnosis of allergic asthma.1 On the other hand, molecular diagnosis also underlines new questions, as described here.

An otherwise healthy nurse, aged 28 years, experienced onset of asthma symptoms soon after being located to a healthcare facility, hosting patients with disabling neuromuscular diseases. ImmunoCap (ThermoFisher Scientific, Uppsala, Sweden) revealed the presence of IgE specific to latex and its main allergic component, Hev b 5 (table 1), the clinical significance of which was uncertain since the patient did not report urticaria on contact with latex gloves and had been previously exposed to latex without clinical events. Sensitisation to peach lipid transfer protein (LTP), Pru p 3, a member of the non-specific lipid transfer protein (nsLTP) superfamily, was detected as well but it was judged clinically irrelevant, since the patient tolerated the ingestion of LTP-containing foods. Despite full compliance with measures to avoid latex exposure and with optimised Global Initiative for Asthma (GINA) step 4 asthma treatment,2 wheezing episodes continued to occur and the patient was referred to our centre for further investigation. We soon discovered she used to feed patients with dysphagia with guar gum-thickened liquid foods. Prick-by-prick test with guar flour resulted positive (5/10?mm) and an increase in antiguar gum IgE title (table 1) was documented. Since daily exposure to guar flour was closely related to appearance of symptoms, a diagnostic specific bronchial challenge with guar flour was considered unnecessary. The patient was relocated to another unit, where she had no further exposure to guar flour, with prompt remission of asthma symptoms.

Table 1
Allergenic components Specific IgE (kUa/L)
Pru p 1 <0.1
Pru p 3 (peach LTP) 0.84
Pru p 4 <0.1
Hev b 1 <0.1
Hev b 3 <0.1
Hev b 5 3.6
Hev b 6.01 <0.1
Hev b 6.02 <0.1
Hev b 8 <0.1
Hev b 9 <0.1
Hev b 11 <0.1
Phl p 1 <0.1
Phl p 12 <0.1
Allergenic extracts
Latex 2.34
Dermatophagoides pter. <0.1
Dermatophagoides far. <0.1
Timothy grass <0.1
Alternaria alternata <0.1
Guar gum (E412) 6.34
Carob gum (E410) 0.14
Arabic gum (E414) <0.1
Tragacanth gum (E413) <0.1
Bold type are positive results

LTP, lipid transfer protein.

Guar gum, a powder obtained from the seeds of Cyamopsis tetragonolobus is used as a thickener in commercial food processing and has been recognised as a cause of occupational rhinitis3 and asthma.4 Galactomannan, a carbohydrate which constitutes 90%–95% of guar flour, is presumed to be its major allergen but the protein fraction may also contain minor allergens. We speculate that our patient’s sensitisation to peach LTP might be underpinned by primary sensitisation to a yet to be discovered guar LTP. Indeed, a protein component with molecular weight and disulfide bonds resembling those of nsLTPs has been described in the foaming fraction of guar meal,5 by which the gum might be contaminated during the extraction process.

To summarise, a detailed and timely allergy investigation, extended to unusual aeroallergens, is mandatory whenever new respiratory symptoms ensue after a variation in patients’ habits or occupation. Especially in the setting of work-related asthma, difficult-to-control asthma can be associated with exposure to unknown or hidden occupational allergens. We also suggest that positive testing for extracts or molecular components without straight clinical correlates should not be overlooked as it might underpin a breakdown in immune tolerance worthy of additional investigation. We propose that guar gum-related occupational asthma might be caused by an LTP component, similarly to wheat LTP-associated bakers’ asthma.6

References
1. Raulf M, Quirce S , Vandenplas O . Addressing molecular diagnosis of occupational allergies. Curr Allergy Asthma Rep 2018;18:6.doi:10.1007/s11882-018-0759-9
2. Global Initiative for Asthma. Global strategy for asthma management and prevention, 2019
3. Kanerva L , Tupasela O , Jolanki R , et al . Occupational allergic rhinitis from guar gum. Clin Allergy 1988;18:245–52.doi:10.1111/j.1365-2222.1988.tb02866.x
4. Lagier F , Cartier A , Somer J , et al . Occupational asthma caused by guar gum. J Allergy Clin Immunol 1990;85:785–90.doi:10.1016/0091-6749(90)90199-E
5. Shimoyama A , Kido S , Kinekawa Y-ichi , et al . Guar foaming albumin: a low molecular mass protein with high foaming activity and foam stability isolated from guar meal. J Agric Food Chem 2008;56:9200–5.doi:10.1021/jf8010323 PubMedGoogle Scholar
6. Armentia A , Garrido-Arandia M , Cubells-Baeza N , et al . Bronchial challenge with tri a 14 as an alternative diagnostic test for baker's asthma. J Investig Allergol Clin Immunol 2015;25:352–7.Google Scholar

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