"THREE FACES OF HOUSE DUST MITE ALLERGY: DISTINCT CLINICAL PHENOTYPES OF DF-ONLY, DP-ONLY, AND DUAL HDM SENSITIZATION IN AN INDIAN COHORT"

House dust mite (HDM) allergy belongs to the most important allergies and affects approximately 65–130 million people worldwide. House dust mites (HDMs) are extensively reported as potent allergens worldwide with India being in the top row. HDM sensitization is hugely reported from India and has led to the concern of implementing proper guidelines for treatment of the sufferers. Climatic conditions and a rapid shift of life style toward a more indoor and urbanised pattern are denoted as the probable causes of increased HDM exposure and sensitization. On the contrary, the varying rate of HDM allergy from similar climate and urbanised areas throughout the world suggest the influence of genetic predisposition. At present, in India, avoidance of HDM exposure is recommended as the baseline defence. Allergen immunotherapy (AIT) guidelines are proposed in India to maintain uniformity in the diagnosis techniques and management strategies throughout the country. Considering the genetic susceptibility toward allergic diseases, the concept of 'personalised medicine' is preferred over the 'mass targeted treatment'. From the Indian perspective, the present problem is Dermatophagoides pteronyssinus and D. farinae allergens are not well characterised at the molecular level. Background: House dust mite (HDM) sensitization is a major driver of allergic rhinitis and asthma worldwide, particularly in humid and tropical climates. Dermatophagoides farinae (Df) and Dermatophagoides pteronyssinus (Dp) are the predominant HDM species, but the clinical differences between Df-only, Dp-only and dual Df+Dp sensitization are not well defined in Indian populations. Objective: To characterise the prevalence and clinical phenotypes associated with Df-only, Dp-only and dual Df+Dp sensitization in young adults undergoing skin prick testing (SPT) at a tertiary allergy centre. Methods: Of 110 participants undergoing SPT with a 33-allergen aeroallergen panel, 97 tests were valid and analysed. Sensitization to Df (allergen 1) and Dp (allergen 2) was used to classify participants into four groups: Df-only, Dp-only, Df+Dp and HDM-negative. Clinical data and pseudopod reactions were evaluated. Statistical associations between Df and Dp sensitization were explored. Results: HDM sensitization (Df and/or Dp) was present in 43/97 (44.3%) participants. Df-only sensitization occurred in 11 (11.3%), Dp-only in 5 (5.1%) and dual Df+Dp sensitization in 27 (27.8%), while 54 (55.7%) were HDM-negative. Df-only subjects displayed a milder phenotype, predominantly with intermittent rhinitis and minimal airway involvement. Dp-only participants exhibited a more airway-dominant profile. Dual Df+Dp sensitization was associated with the highest burden of persistent rhinitis, wheeze, polysensitization and pseudopod formation, suggesting a high Th2-load phenotype. Df and Dp co-sensitization showed a strong statistical association (odds ratio ≈ 3.0; p < 0.05). HDM-negative subjects tended to have pollen- or irritant-related symptoms. Conclusion: Df-only, Dp-only and dual Df+Dp sensitization represent distinct clinical and immunological phenotypes in this cohort, with dual HDM sensitization marking the most severe allergic burden. Phenotyping HDM sensitization may refine risk stratification and selection for allergen immunotherapy.