The spectrum of CFTR mutations in south-west German cystic fibrosis patients

Acute Recurrent Pancreatitis in a Child With INS-Related Monogenic Diabetes and a Heterozygous Pathogenic CFTR Mutation

Given the close anatomical and physiological links between the exocrine and endocrine pancreas, diseases of 1 compartment often affect the other through mechanisms that remain poorly understood. Pancreatitis has been associated with both type 1 and type 2 diabetes, but its association with monogenic diabetes is unknown. Patients heterozygous for pathogenic CFTR variants are cystic fibrosis carriers and have been reported to have an increased risk of acute pancreatitis. We describe a 12-year-old patient with monogenic neonatal diabetes due to a pathogenic heterozygous paternally inherited mutation of the insulin gene (INS), c.94 G > A (p.Gly32Ser), who experienced 3 recurrent episodes of acute pancreatitis over 7 months in conjunction with poor glycemic control, despite extensive efforts to improve glycemic control in the past 4 years. Intriguingly, the maternal side of the family has an extensive history of adult-onset pancreatitis consistent with autosomal dominant inheritance and the proband is heterozygous for a maternally inherited, CFTR variant c.3909C > G (p.Asn1303Lys). Paternally inherited monogenic neonatal diabetes may have promoted earlier age-of-onset of pancreatitis in this pediatric patient compared to maternal relatives with adult-onset acute pancreatitis. Further study is needed to clarify how separate pathophysiologies associated with INS and CFTR mutations influence interactions between the endocrine and exocrine pancreas.

Final results of the southwest German pilot study on cystic fibrosis newborn screening - Evaluation of an IRT/PAP protocol with IRT-dependent safety net: Results of the Southwest German CFNBS pilot study

BACKGROUND

Previous studies suggest that PAP-based CF protocols are suitable for newborn screening (NBS) for cystic fibrosis (CF) when newborns designated as CFSPID should not be detected. However, there are still discussions about the performance of IRT/PAP algorithms. We present the final results of a pilot study evaluating a IRT/PAP protocol with an IRT-dependent safety net (SN) conducted from 2008 to 2016 in southwestern Germany on nearly 500,000 newborns.

METHODS

To achieve reliable data, all newborns were screened using both the PAP-based and a DNA-based CFNBS algorithm. PAP quantification and genetic analysis of the four most common CFTR mutations in Germany were performed in all newborns with IRT≥99.0 percentile. NBS was rated positive if either PAP was ≥1.6 µg/l and/or at least one CFTR mutation was detected. In addition, an IRT-dependent SN resulted in positive rating for both protocols if IRT was ≥99.9 percentile. To evaluate the IRT/PAP protocol, its performance was compared to that of the IRT/DNA protocol.

RESULTS

The IRT/PAP protocol with IRT-based SN used in the study achieved a sensitivity of 94%, if false-negative detected neonates with meconium ileus and those designated as CFSPID were excluded from analysis. CF/CFSPID ratio was 92. However, PPV of the IRT/PAP+SN protocol was with 10.3% very low.

CONCLUSIONS

PAP-based CFNBS protocols can be used, if less detection of CFSPID is desired. The IRT/PAP protocol with IRT-dependent SN evaluated here achieved adequate sensitivity but should probably be used in combination with a third-tier test to also achieve an acceptable PPV.

Five years of experience with biochemical cystic fibrosis newborn screening based on IRT/PAP in Germany

BACKGROUND

Evidence from recent studies suggests that IRT/PAP protocols may be successfully used as a purely biochemical newborn screening (NBS) for cystic fibrosis (CF) that does not require genetic screening. However, the experience with the performance of different IRT/PAP protocols remains limited. In this study, we evaluated the performance of IRT/PAP-based CF-NBS used in two German regions between 2008 and 2013 in a large cohort.

METHODS

In both regions slightly different IRT/PAP protocols were used to screen newborns for CF. In contrast to the original IRT/PAP protocol published by Sarles et al., both German protocols contained an IRT-dependent safety net strategy (CF-NBS positive, if IRT≥99.9th percentile). Positive rating of the screening result led to confirmatory diagnostics using sweat chloride testing and clinical assessment.

FINDINGS

A total of 328,181 newborns were tested with IRT/PAP in Germany within 5 years. 639 of these newborns (0.19%) were tested positive, and 60 infants were diagnosed with CF leading to a sensitivity of 0.968 and a PPV (positive predictive value) of 0.097. Compared to IRT/DNA protocols, the PPV of IRT/PAP is lower, but PAP used as second tier test has the advantage of a lower detection rate of healthy carriers and CF patients with equivocal results.

CONCLUSIONS

Our results obtained in a large cohort of ∼330,000 newborns support the use of a purely biochemical IRT/PAP protocol as an acceptable alternative when genetic CF-NBS has to be avoided.

Initial evaluation of a biochemical cystic fibrosis newborn screening by sequential analysis of immunoreactive trypsinogen and pancreatitis-associated protein (IRT/PAP) as a strategy that does not involve DNA testing in a Northern European population

BACKGROUND

Ethical concerns and disadvantages of newborn screening (NBS) for cystic fibrosis (CF) related to genetic testing have raised controversies and impeded implementation of CF NBS in some countries. In the present study, we used a prospective and sequential immunoreactive trypsinogene (IRT)/pancreatitis-associated protein (PAP) strategy, with IRT as first and PAP as second tier, and validated this biochemical approach against the widely used IRT/DNA protocol in a population-based NBS study in southwest Germany.

METHODS

Prospective quantitation of PAP and genetic analysis for the presence of four mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene most prevalent in southwest Germany (F508del, R553X, G551D, G542X) were performed in all newborns with IRT > 99.0th percentile. NBS was rated positive when either PAP was ≥1.0 ng/mL and/or at least one CFTR mutation was detected. In addition, IRT > 99.9th percentile was also considered a positive rating. Positive rating led to referral to a CF centre for testing of sweat Cl(-) concentration.

FINDINGS

Out of 73,759 newborns tested, 98 (0.13%) were positive with IRT/PAP and 56 (0.08%) with IRT/DNA. After sweat testing of 135 CF NBS-positive infants, 13 were diagnosed with CF. Detection rates were similar for both IRT/PAP and IRT/DNA. One of the 13 diagnosed CF newborns had a PAP concentration <1.0 ng/mL.

CONCLUSIONS

Sequential measurement of IRT/PAP provides good sensitivity and specificity and allows reliable and cost-effective CF NBS which circumvents the necessity of genetic testing with its inherent ethical problems.

F413C and A531V but not R894X myotonia congenita mutations cause defective endoplasmic reticulum export of the muscle-specific chloride channel CLC-1

In northern Finland myotonia congenita is caused by three main mutations in the ClC-1 chloride channel. We studied the molecular basis of these mutations (1238T>G/F413C, 1592C>T/A531V, and 2680C>T/R894X). The mutated cDNAs were expressed either in L6 myotubes or in isolated rat myofibers using recombinant Semliki Forest virus. Experiments in L6 cells indicated that A531V and R894X proteins suffered from stability problems in these cells. Analysis in myofibers indicated that the A531V protein was totally retained in the endoplasmic reticulum (ER), whereas the export of the F413C protein was severely reduced. The C-terminal nonsense mutant (R894X), however, was normally transported to the Golgi elements in the myofibers. Defective export or reduced stability of the mutated proteins may thus be reasons for the myotonic symptoms.

A cystic fibrosis mutation associated with mild lung disease

BACKGROUND

Cystic fibrosis is the most common lethal autosomal recessive disorder among whites. Among Dutch patients with cystic fibrosis, delta F508 is the most common mutation and A455E the second most common mutation of the cystic fibrosis transmembrane conductance regulator gene on chromosome 7. A455E is associated with preserved pancreatic function and residual secretion of chloride across membranes. We investigated whether it is also associated with less severe pulmonary disease in patients with cystic fibrosis.

METHODS

A total of 33 patients with compound heterozygosity for the A455E mutation were matched according to age and sex with patients who were homozygous for the delta F508 mutation. The pairs were analyzed with respect to the following outcome variables: age at diagnosis, pulmonary-function values, and the frequency of pseudomonas colonization, pancreatic sufficiency, and diabetes mellitus.

RESULTS

Cystic fibrosis was diagnosed at a later age in the patients with the A455E mutation than in the delta F508 homozygotes (mean age at diagnosis, 15.0 vs. 3.1 years; P < 0.001). Fewer patients with the A455E mutation had pancreatic insufficiency (21.2 percent vs. 93.9 percent, P < 0.001), and none had diabetes mellitus (0 percent vs. 27.3 percent, P = 0.004). Forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were significantly higher in the patients with the A455E mutation (mean FEV1, 73.9 percent of the predicted value vs. 54.3 percent of the predicted value; P = 0.002; mean FVC, 88.7 percent of the predicted value vs. 76.3 percent of the predicted value; P = 0.04). Fewer patients with the A455E mutation were colonized with Pseudomonas aeruginosa (33.3 percent vs. 60.6 percent, P = 0.02).

CONCLUSIONS

A455E is a common mutation causing cystic fibrosis in the Netherlands. Although several mutations are known to be associated with less severe pancreatic disease, our findings demonstrate a correlation between the A455E mutation and mild pulmonary disease. Because mortality in this disease depends primarily on the progression of pulmonary disease, patients with the A455E mutation have a better prognosis than patients who are homozygous for the delta F508 mutation.