Complex allele [-102T>A+S549R(T>G)] is associated with milder forms of cystic fibrosis than allele S549R(T>G) alone.

We recently reported a novel complex allele in the cystic fibrosis transmembrane regulator (CFTR) gene, combining a sequence change in the minimal CFTR promoter (-102T>A) and a missense mutation in exon 11 [S549R(T>G)]. Here we compare the main clinical features of six patients with cystic fibrosis (CF) carrying the complex allele [-102T>A+S549R(T>G)] with those of 16 CF patients homozygous for mutation S549R(T>G) alone. Age at diagnosis was higher, and current age was significantly higher (P=0.0032) in the group with the complex allele, compared with the S549R/S549R group. Although the proportion of patients with lung colonization was similar in both groups, the age at onset was significantly higher in the group with the complex allele (P=0.0022). Patients with the complex allele also had significantly lower sweat test chloride values (P=0.0028) and better overall clinical scores (P=0.004). None of the 22 patients reported in this study had meconium ileus. All 16 patients homozygous for S549R(T>G), however, were pancreatic insufficient, as compared with 50% of patients carrying the complex allele (P=0.013). Moreover, the unique patient homozygous for [-102T>A+S549R(T>G)] presented with a mild disease at 34 years of age. These observations strongly suggest that the sequence change (-102T>A) in the CFTR minimal promoter could attenuate the severe clinical phenotype associated with mutation S549R(T>G).