Case control studies considered for inclusion in the meta-analyses and patient subclassification within each study.

*Prevalence of the N34S polymorphism was not reported in the control population. **Data duplicated in Schneider et al [55]. ***Data duplicated in Shimosegawa et al [65]. ****Data duplicated in Kume et al[29]. •Dropped from the analysis because it did not identify the N34S polymorphism in either the cases or the controls therefore resulting in a null relative weight. ••Unable to subclassify patients into the mentioned categories due to missing data. PCR: Polymerase Chain Reaction, RFLP: Restricted Fragment Length Polymorphism, DGGE: Denaturing Gradient Gel Electrophoresis.