Many deltaF508 heterozygote neonates with transient hypertrypsinaemia have a second, mild CFTR mutation

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations and risk for pancreatic adenocarcinoma

BACKGROUND

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are common in white persons and are associated with pancreatic disease. The purpose of this case-control study was to determine whether CFTR mutations confer a higher risk of pancreatic cancer.

METHODS

In a case-control study, the authors compared the rates of 39 common cystic fibrosis-associated CFTR mutations between 949 white patients with pancreatic adenocarcinoma and 13,340 white controls from a clinical laboratory database for prenatal testing for CFTR mutations. The main outcome measure was the CFTR mutation frequency in patients and controls.

RESULTS

Overall, 50 (5.3%) of 949 patients with pancreatic cancer carried a common CFTR mutation versus 510 (3.8%) of 13,340 controls (odds ratio [OR], 1.40; 95% confidence interval [CI], 1.04-1.89; P = .027). Among patients who were younger when their disease was diagnosed (<60 years), the carrier frequency was higher than in controls (OR, 1.82; 95% CI, 1.14-2.94; P = .011). In patient-only analyses, the presence of a mutation was associated with younger age (median 62 vs 67 years; P = .034). In subgroups, the difference was seen only among ever-smokers (60 vs 65 years, P = .028). Subsequent sequencing analysis of the CFTR gene detected 8 (16%) compound heterozygotes among the 50 patients initially detected to have 1 mutation.

CONCLUSIONS

Carrying a disease-associated mutation in CFTR is associated with a modest increase in risk for pancreatic cancer. Those affected appear to be diagnosed at a younger age, especially among smokers. Clinical evidence of antecedent pancreatitis was uncommon among both carriers and noncarriers of CFTR mutations.

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.

Immunoreactive trypsin/DNA newborn screening for cystic fibrosis: should the R117H variant be included in CFTR mutation panels?

BACKGROUND

Cystic fibrosis newborn screening is now implemented universally in France, as well as in many states in the United States and in various areas of Europe and Australia. Because the screening protocol usually includes the analysis of the most common CFTR mutations, it is of the utmost importance that only mutations that result in classical cystic fibrosis are included in this test. The panels of mutations used in most cystic fibrosis newborn screening programs enable the detection of a relatively frequent CFTR variant (R117H) whose implication in cystic fibrosis remains unclear. Physicians, therefore, have difficulty managing detected compound heterozygotes with this variant, which raises the issue of the appropriateness of extended testing in families and of the legitimate use of prenatal diagnosis.

OBJECTIVE

The aim of this study was to describe the clinical outcome of the children found to be compound heterozygous for R117H by screening in Brittany (western France), where cystic fibrosis newborn screening was set up in 1989, and to assess whether this CFTR variant should be included in the newborn screening mutation panels.

METHODS

Data on clinical status were obtained by the referring pediatricians.

RESULTS

Since our screening protocol has enabled detection of R117H (ie, in 1995), 360466 newborns have been screened for cystic fibrosis in Brittany, of whom 124 had elevated immunoreactive trypsin and 2 mutations in the CFTR gene. Nine of these children (7.3%) were compound heterozygous for R117H, which in all cases was linked to the 7T_11TG haplotype [IVS8-nT variant/m(TG) repeat]. Their genotypes were F508del/R117H (n = 7), I507del/R117H (n = 1), or G551D/R117H (n = 1). At the time of this writing, the mean age of these 9 children was 7.0 years (the oldest being >10 years of age), and none of them had yet developed any signs of cystic fibrosis; they have been pancreatic sufficient and have had good nutritional status and pulmonary function. Moreover, we observed that, in Brittany, all the patients carrying the R117H variant have been identified exclusively through cystic fibrosis newborn screening.

CONCLUSIONS

In view of the high frequency of R117H-7T identified by cystic fibrosis newborn screening, the uncertain outcome of the asymptomatic children, and physicians' difficulty in managing these situations, we propose the withdrawal of the R117H variant from the panels of CFTR mutations used in cystic fibrosis newborn screening, given the expanding implementation of cystic fibrosis newborn screening.

Cystic fibrosis carriers have higher neonatal immunoreactive trypsinogen values than non-carriers

Following cystic fibrosis (CF) neonatal screening implementation, a high frequency of heterozygotes has been reported among neonates with elevated immunoreactive trypsinogen (IRT) and normal sweat chloride levels. We studied the relationship between normal IRT values and CF heterozygosity: 10,000 neonates were screened for CF by IRT measurement and tested for 40 CF mutations; the 294 carriers detected were coupled with newborns negative to the same genetic testing, and the two groups' IRT levels compared. Heterozygotes had higher IRT levels than their controls (mean 35.32 vs. 27.58 microg/L, P<0.001). Even within normal trypsinogen range, the probability of being a CF carrier increases with neonatal IRT concentration.

Newborn screening programmes for cystic fibrosis

We review the current situation with respect to newborn cystic fibrosis screening (NCFS) across the world. The challenges of establishing an NCFS programme are reflected in the diversity of those programmes identified. All employ an initial immunoreactive trypsinogen (IRT) measurement during the first week of life. If this is positive, a second IRT analysis at 4 weeks of age improves the specificity of the test; most programmes have, however, moved to DNA analysis at this point, which improves their sensitivity. Incorporating DNA analysis results in the identification of carriers, which may have implications for families but is generally considered positive. Some programmes have incorporated a second IRT test as well as DNA analysis, either to increase the sensitivity of the test in an area with a low DeltaF508 frequency or to reduce the number of infants requiring a sweat test. Whichever algorithm is selected, the implementation of a successful programme relies on clear pathways and good information for parents.

Comparison of two different protocols of neonatal screening for cystic fibrosis

The results of two different protocols of neonatal cystic fibrosis (CF) screening in the Lazio region of Italy are reported. The first study, conducted from 1992 to 2000 on about 200,000 newborns, consisted of an immunoreactive trypsin (IRT) protocol without mutation analysis of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, referred to as the IRT/IRT protocol. Approximately 5% of the newborns with a positive first IRT test were also positive at the second test; approximately 57% of the newborns with a high IRT level at the second test were subsequently found to be affected by CF. In September 1998, a second protocol that included mutation analysis (IRT/DNA/IRT protocol) was started. Comparison of the two different screening protocols in terms of sensitivity in detecting CF patients demonstrated that the IRT/DNA/IRT protocol is more effective because it is able to detect a higher number of CF patients than the IRT/IRT protocol. In the same period, in addition to the overall diagnosis performed on a screening basis, 64 other subjects were identified as being affected by CF on the basis of symptomatic findings. The overall incidence of CF (screening + symptoms) was 1 : 2982, while that for carriers was 1 : 27. The sensitivity of the screening program increased over the period from 1992 to 2000, with the enhanced sensitivity in the past 2 years being due to the introduction of the IRT/DNA/IRT protocol.

Cystic fibrosis screening in newborns: results from existing programs

Newborn screening for cystic fibrosis (CF) provides early identification and initiation of treatment to infants with this fatal and often misdiagnosed genetic disease. Although reports of health benefits continue to mount from decade-old screening programs in Wisconsin, France, and Australia, newborn screening for CF is still a highly debated topic in genetic policy development. This article summarizes the literature published between May 2000 and April 2001 regarding the health benefits, risks, cost-effectiveness, and programmatic issues of newborn screening for CF. The literature consistently shows evidence of benefits and lack of harm from newborn screening for CF.