Abstract: The present invention concerns a method of testing a subject thought to have or be predisposed to having asthma, allergy, atopic disease or atopic sensitization, which comprises the step of analyzing a biological sample from said subject for (i) detecting the presence of a mutation associated with the over-expression of the ORMDL3 gene, and/or (ii) analyzing the expression of the ORMDL3 gene; a use, for treating and/or preventing asthma, allergy, atopic disease or atopic sensitization in a subject, of a compound which specifically inhibits the expression of the ORMDL3 gene; and an in vitro method of selecting a compound, which can be useful for treating asthma, allergy, atopic disease or atopic sensitization, characterized in that said method comprises the steps of: (a) obtaining a cell expressing the ORMDL3 gene, (b) contacting said cell with at least one compound, (c) comparing the expression of the ORMDL3 gene in the cell between the steps a) and b), and (d) selecting the compound, which induces a lower le