PTGDR and allergic disease: We selected PTGDR2 for several reasons: it was one of the five most differentially overexpressed coding transcripts in asthmatic patients (fold change 1.989; p-value 2.64 × 106) (Table 2) the role of PGD2 and their receptors, PTGDR1 and PTGDR2, in asthma and allergy [16,29,30,31], and mainly because there are several drugs directed against the receptor in development [32].