According to the GRADE system, the certainty of evidence for the asthma daytime and nighttime symptom scores, FEV1, FVC, PEF, and the levels of TNF-α, IFN-γ, and IL-4 was classified as very low, underscoring the need for additional rigorously designed studies to validate these findings (Table 2). This evidence concerns the gene IL4 and asthma.