Characteristics of studies included in meta-analysis.

<p>NA, not available; PCR, polymerase chain reaction; RFLP, restricted fragment length polymorphisms; SSP, sequence.</p><p>-specific primers; SPT, skin prick test; BHR,bronchial hyperresponsiveness; TDI, toluene diisocyanate; ARMS, amplification refractory mutation system;Mixed, participants involved children and adults.