Chouchane et al. (1999) conducted a study to investigate the role of a repeat polymorphism in the IL4 gene in the pathogenesis of asthma among Tunisians. A total of 145 asthma patients (49 females, 86 males) were included in the study, and were classified into mild or moderate/severe asthma according to the clinical features before treatment and the lung function. In addition, a group of 160 healthy subjects (63 females, 97 males; mean age: 14 yrs) with no familial history of asthma was also selected for the study as control. The control subjects showed no specific IgE reaction. Genomic DNA, extracted from the blood of the subjects was amplified using a PCR primer intending to type a repeat polymorphism in intron 2 of the IL4 gene. Three allelic forms were identified: A1 (171 bp), A2 (161 bp), and A3 (149 bp). The patient group showed a high number of A1/A3 genotype, whereas the control group showed a significant decrease in the A3/A3 genotype. The frequency of the A1 allele was therefore, significantly increased in the patient population. Four patients with the A1 allele were selected for family studies. In two of these families, the IL4 A1 allele showed a recessive mode of inheritance, with only homozygous A1/A1 members showing the disease. In the two other families, members with the A1/A3 genotype were found to be asthmatic. In addition, in patients with moderate/severe asthma, the frequency of the A1 allele and the A1/A3 genotype was found to be significantly higher (0.36 and 0.475) as compared to patients with mild asthma (0.08 and 0.075). The relative risk of moderate/severe asthma associated with the A1/A3 genotype was found to be 3.94, while with the A3/A3 genotype, it was 0.165. Chouchane et al. (1999) explained the association found between the polymorphism and asthma as arising either from the IL4 intron 2 carrying a mast-cell specific enhancer, or by the polymorphism being in linkage disequilibrium with a locus contributing to the onset of asthma.