Mild pulmonary disease in a cystic fibrosis child homozygous for R553X.

Nonsense mutations frequently cause severe illness because premature termination of messenger RNA translation usually creates un-stable truncated proteins. However, Cutting et al described two patients carrying nonsense mutations in each cystic fibrosis gene (G542X/ S1255X and R553X/W1316X) with severe pancreatic involvement but mild pulmonary disease. Furthermore, Cuppens et al and Bonduelle et al described children homozygous for the G542X stop mutation who were only mildly affected. Recently, Bal et a1 reported a patient homozygous for the R553X nonsense mutation who was moderately severely affected. We present the clinical and molecular findings of a child also homozygous for R553X but with mild pulmonary disease.