First report of three cystic fibrosis patients homozygous for the 1717-1G-->A mutation

Molecular and clinical features associated with CFTR gene rearrangements in Italian population: identification of a new duplication and recurrent deletions

Cystic fibrosis (CF) is mainly caused by small deletions or missense mutations in the CFTR gene. The CF mutation database lists more than 35 large rearrangements that may escape detection using polymerase chain reaction-base techniques. The Innogenetics assay, the denaturing high-performance liquid chromatography and sequencing screening showed a mutation detection rate of 92.6% in our population. We report here the results of multiplex ligation-dependent probe amplification (MLPA) screening for CFTR gene rearrangements, performed on the unidentified alleles of our CF patients. Our sample population consists of 692 non-related Italian CF patients (for a total of 1384 alleles), followed at CF Centres in the Lombardia Region. MLPA analysis was performed in 49 patients who still had one or two unidentified alleles (for a total of 52 unidentified alleles) after extensive analysis of CFTR gene. All patients who were studied had the classical form of CF. We characterized nine different deletions and a new duplication. The deletion of exons 22-23 (7/82) was the most frequent in our cohort. The search for deletion/duplications of the CFTR gene has made it possible to reach a 94.1% detection rate, with an improvement (1.6%) of the carrier detection rate in the Italian population.

Does cystic fibrosis neonatal screening detect atypical CF forms? Extended genetic characterization and 4-year clinical follow-up

The neonatal screening protocol for cystic fibrosis (CF) is based on a first determination of blood immunoreactive trypsin (IRT1), followed by a first level genetic test that includes the 31 worldwide most common mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene (DNA31), and a second determination of blood immunoreactive trypsin (IRT2). This approach identifies, in addition to affected subjects, a high proportion of newborns with hypertrypsinaemia at birth, in whom only one mutation is identified and who have a negative or borderline sweat test and pancreatic sufficiency. Although it has been suggested that hypertrypsinaemia may be caused by a single CFTR mutation, whether such neonates should be merely considered as healthy carriers remains a matter of debate as hypertrypsinaemia at birth may be a biochemical marker of a CFTR malfunction because of a second mild mutation. We analyzed, by means of an extended sequencing protocol, 32 newborns who tested positive at an IRT1/DNA31/IRT2 screening protocol and in whom only one CFTR mutation was found. The results obtained demonstrate that 62.5% of these newborns were also carrying a second mild CFTR mutation. The high proportion of compound heterozygous subjects, combined with the results of a 4-year follow-up in nine of these subjects all of whom displaying initial CF clinical symptoms, suggest that it may be possible to use the IRT1/DNA31/IRT2 protocol of neonatal screening to identify newborns with atypical forms of CF. In view of these findings, an extended genetic search for subjects with compound heterozygosity and a periodic clinical assessment should be considered.

Normal volume of distribution of tobramycin in a mother and daughter with a CFTR splice mutation (1717 - 1G --> A)

A mother and daughter pair with CF who shared a splice mutation (1717 - 1G --> A) had a normal volume of distribution of tobramycin. The literature on tobramycin pharmacokinetics, which was published before the genetic defect was identified, is discussed. The authors speculate on the role of CFTR in the distribution of aminoglycosides and recommend that CFTR mutations should be clarified in all future studies of tobramycin pharmacokinetics in patients with CF.