False negative results on newborn screening for cystic fibrosis

Over a 5 year period in Newcastle, 18 new cases of cystic fibrosis (CF) were diagnosed in children who had been screened in the newborn period. In six of these children, the screening programme failed. Four of these children had a normal screen and an additional two had elevated immunoreactive trypsin (IRT), but there were problems with the notification procedure. Three of the children missed by the screening process had a significantly delayed diagnosis; in all three cases the diagnosis of CF was suspected clinically, but a sweat test was delayed because of false reassurance from the fact that the child had been screened for CF. In a fourth case, multiple elevated sweat electrolyte levels were obtained, but the diagnosis of CF was considered to be in doubt because of the normal IRT assay. A sweat test should be performed on any child in whom there is clinical suspicion of CF.     

Community-wide screening for cystic fibrosis carriers could replace newborn screening for the diagnosis of cystic fibrosis

Most babies with cystic fibrosis (CF) are born to parents who did not know they were carriers until their baby was diagnosed with CF, usually by newborn screening. It is only after the birth of their first child with CF that couples are offered genetic counselling and reproductive choices. Most use this information for prenatal testing of subsequent pregnancies. With the high uptake of first trimester screening for Down syndrome (80% in Victoria) most couples have had screening during the CF affected pregnancy. Yet screening for CF carrier status is available, costs are similar to that for Down syndrome screening and CF carrier screening only ever needs to be done once. Waiting for couples to have a baby with CF before they are identified as carriers denies them choice. A national policy on CF carrier screening in Australia, and determination to equitably fund such a programme, is required.     

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.     

Markedly elevated neonatal immunoreactive trypsinogen levels in the absence of cystic fibrosis gene mutations is not an indication for further testing

Aims

To investigate the immunoreactive trypsinogen (IRT) values above the usual 99th centile laboratory cut‐off and determine the value of offering further testing to those infants with a markedly elevated IRT but no cystic fibrosis transmembrane regulator (CFTR) gene mutation identified by the screening programme.

Methods

All babies born in Victoria, Australia, between 1991 and 2003, were screened by IRT followed by CF gene mutation analysis.

Results

Of the 806 520 babies born, 9268 with the highest IRT levels had CFTR mutation analysis. There were 123 ΔF508 homozygotes and 703 heterozygotes (86 with CF, 617 carriers). A total of 8442 babies had no CFTR gene mutation, of whom 18 (0.21%) had CF. The total number of CF babies with IRT greater than the laboratory cut‐off was 227 (2.4%). The IRT results of the CF patients were distributed normally, with the majority above the laboratory cut‐off of newborn IRT results. There was no evidence of an excess of babies with CF in the very highest levels of IRT above the 99th centile.

Conclusions

Only a small proportion of babies with a neonatal IRT >99th centile have CF. Additional CF testing for infants with an elevated IRT but no CFTR gene mutation has an extremely low yield, no matter how high the IRT result.     

Psychosocial issues in newborn screening for cystic fibrosis

Newborn screening for cystic fibrosis remains controversial because there is still little agreement that prophylactic interventions provide substantial long-term benefits. In such situations, where there are some medical benefits and the costs are not prohibitive, it is important to consider the psychosocial implications of screening. This paper reviews the evidence on the psychosocial issues raised by newborn screening for cystic fibrosis, in particular the issues of parental attitudes to screening, the evidence from families with an affected infant, the evidence from families with a carrier infant and the lessons for service delivery.     

Parental attitudes to the identification of their infants as carriers of cystic fibrosis by newborn screening

AIM: To investigate parental attitudes to cystic fibrosis (CF) carrier detection of their infant by newborn screening (NBS). METHODS: Data were collected from a postal questionnaire sent to parents of infants identified as CF carriers by NBS in 1996-1997 (inclusive) and 2001 in Victoria, Australia (n = 66). RESULTS: Almost all parents remembered their child being identified as a CF carrier (97%: 1996/1997; 100%: 2001); yet the majority were unaware at the time that NBS could detect carriers (70%: 1996/1997; 49%: 2001). More parents in the later cohort reported having carrier testing compared with the earlier cohort (85% and 53% respectively) but recall was more uncertain in the earlier cohort when validated against health records. Cascade testing was not utilised frequently by other family members in either cohort. Residual risk of being a carrier if testing was negative was not well understood by parents. Some parents (28%: 1996/1997; 18%: 2001) had residual anxiety about the current health of their carrier child and their future reproductive decision making. Most parents were satisfied with the information provided to them at the time of the sweat test. Few differences were seen between the cohorts. CONCLUSION: Although the NBS process for CF in Victoria is working efficiently for the majority of families whose infant is identified as a carrier there are areas that can be improved. We recommend that greater attention should be given to informing parents that a consequence of NBS is CF carrier detection and strategies to improve utilisation of cascade testing should be developed.     

Vitamin D in infants with cystic fibrosis diagnosed by newborn screening

Aims:   Screening enables early nutritional deficiencies to be detected in those with cystic fibrosis (CF). Although vitamin deficiency is considered unlikely in older subjects with normal vitamin E levels, few studies have determined vitamin D status at diagnosis and its relationship to other fat-soluble vitamins.
Methods:   We reviewed vitamin levels in infants diagnosed with CF by newborn screening over a 5-year period in Melbourne, Australia. Vitamin D levels were determined using the IDS gamma-B 25-OH Vitamin D radio-immunoassay (Immunodiagnostic Systems Limited, Boldon, UK). Vitamins A and E were evaluated by high-performance liquid chromatography. We assessed the association between vitamin D level and sex, month of birth, pancreatic status, and vitamin A and E levels.
Results:   Fifty-eight infants were diagnosed at a median age of 1 month (range: 0–3 months). Initial vitamin D levels were assessed between 0.2 and 3.5 months in 30 (vitamin D) and 45 (vitamins A and E) infants. The number of infants deficient with vitamins D, E and A were 11 (37%), 7 (16%) and 27 (60%), respectively. Vitamin D levels were unrelated to sex, vitamin A or E levels, month of birth or pancreatic status, whereas vitamin A and E levels were significantly lower in those who were pancreatic insufficient. With supplementation, vitamin D increased over time.
Conclusions:   Vitamin D deficiency is common in infants newly diagnosed with CF by newborn screening and is unrelated to pancreatic status or predicted low vitamin E levels. Vitamin D deficiency is less common over time following treatment.     

Metabolic alkalosis with hypoelectrolytemia in infants with cystic fibrosis

BACKGROUND: Infants with cystic fibrosis (CF) can develop episodes of hyponatremic hypochloremic dehydration with metabolic alkalosis when they sweat excessively, which is not caused by sweating in normal infants. We investigated the incidence of the metabolic alkalosis with hypoelectrolytemia in CF infants, the possible risk factors for its occurrence and the importance of the manifestation in the diagnosis of CF. METHODS: In order to evaluate the incidence and the risk factors for the development of this sweat-related metabolic disorder in CF, we reviewed the records of all children diagnosed as having CF before the age of 12 months in a 10-year period. Data analysis included medical history data, clinical features, biochemical parameters (blood pH, serum bicarbonate, sodium, chloride and potassium levels), sweat chloride test values, as well as genetic analysis data. RESULTS: The prevalence of metabolic alkalosis in association with low serum electrolyte concentrations (hyponatremia, hypochloremia, and hypokalemia) in infant CF population in our region was 16.5%. We found no season predilection in its occurrence. Early infant age, breast-feeding, delayed CF diagnosis, heat exhaustion and the presence of severe CF transmembrane conductance regulator mutations are predisposed factors for the development of metabolic alkalosis with hypoelectrolytemia. CONCLUSIONS: The results from our study suggest that metabolic alkalosis with hypoelectrolytemia is a relatively common manifestation of CF in infancy. The possibility of CF should be seriously considered in any infant with this metabolic disorder.     

Protein–energy malnutrition as the first manifestation of cystic fibrosis in infancy

Background:  The protein–energy malnutrition (PEM) that is characterized by hypoproteinemia, edema, and anemia has been reported in 5–13% of infants with cystic fibrosis (CF). Due to the surprising higher incidence of PEM as the first presenting manifestation of CF in Macedonia, the aim of the present study was to evaluate the possible risk factors in its development.
Methods:  Clinical and laboratory profiles (hemoglobin, red blood cell count, total serum protein, serum albumin and liver enzyme levels) and genotype data were analyzed in 115 newly diagnosed infants with CF, during the period 1990–2006.
Results:  PEM manifested in 39 CF infants (33%), usually within the first 5 months of life and in breast-fed infants. Mean hemoglobin, red blood cell count, total serum protein and serum albumin values in the PEM subgroup were, respectively, 76.0 g/L, 2.4 × 10¹²/L, 38.0 g/L and 16.6 g/L. Clinically significant liver involvement was found in 22 patients (56.4%) with PEM. Concerning the molecular basis of CF in these patients, PEM was always associated with ▵F508 , G542X , N1303K and other severe mutations.
Conclusion:  PEM is a common manifestation of CF in infancy. Early infant age, breast-feeding, impaired liver function and the presence of severe cystic fibrosis transmembrane conductance regulator mutations are predisposing factors for the development of PEM.     

Experience with neonatal screening for cystic fibrosis in New Zealand using measurement of immunoreactive trypsinogen

Abstract Neonatal cystic fibrosis (CF) screening has been performed in New Zealand for a total of 7 years. This study reports the experience with this procedure in New Zealand over a 4 year period and compares it with 2 years when diagnoses of CF were suggested by clinical features only. A total of 72 infants were confirmed as having CF during 4 years of screening. Twenty-eight infants were found to have CF during 2 years in which screening was not performed. There were 29 false positive diagnoses during the screening years and six false negative diagnoses. Three of the false negative diagnoses occurred because of laboratory error, but three occurred because either the first or second measurement of immunoreactive trypsinogen (IRT) was normal. Faecal chymotrypsin was measured in samples from 434 infants at the time of the second IRT and assisted with the diagnosis for one infant which might otherwise have been missed. Only 42.5% of infants were asymptomatic at the time of the confirmatory sweat test. Significant morbidity and mortality was associated with meconium ileus which occurred in 24% of infants with CF. Improved ascertainment of cases of CF has occurred since screening began. Further follow-up is required to determine other benefits of newborn screening.     

Identification of the 5T-12TG allele of the cystic fibrosis transmembrane conductance regulator gene in hypertrypsinaemic newborns

In order to increase knowledge of the pathogenic effect of the 5T-12TG allele of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, we evaluated its presence in 24 hypertrypsinaemic newborns with borderline sweat tests. Among 20 CFTR-identified alterations, the 5T-12TG haplotype was the second most frequent mutation (14.6%) over F508del. Conclusion: Our study suggests the need for searching for this allele in hypertrypsinaemic infants with inconclusive sweat tests.     

Delta-F508 cystic fibrosis mutation is not linked to intussusception: implications for rotavirus vaccine

Objective: To determine whether the cystic fibrosis (CF) delta-F508 gene mutation predisposes to intussusception, and so selects infants who should not receive rotavirus vaccine. METHODS: Stored neonatal screening blood spots, retrieved from 81 infants with intussusception and from 79 controls, were tested for the presence of the CF delta-F508 gene mutation. RESULTS: Prevalence of the mutation was similar in blood specimens from intussusception patients and from controls. Conclusion: Testing for the CF delta-F508 mutation at birth is unlikely to identify infants predisposed to intussusception, and therefore is not relevant to rotavirus vaccine programs.     

The prognosis of cystic fibrosis in the Western Cape region of South Africa

Objective : To study the prognosis of cystic fibrosis (CF) in South Africa.
Methodology : Retrospective chart review of 102 children with CF over 20 years.
Results : Survival at 18 years was 54% (95% confidence intervals 30–79). Prognosis was not influenced by gender or genotype but survival was noted to be worse for Cape Coloured children than for European children. This appeared mainly to be due to the death of eight Cape Coloured infants, four of whom presented with oedema and anaemia, mimicking kwashiorkor. Infection with Pseudomonas aeruginosa occurred earlier in Cape Coloured children than European children (median, 1 vs 4 years) and they had a worse 5-year survival (56 vs 89%, P < 0.05) after infection. Of the 40 children born in the second decade studied, six Coloured and no European children died.
Conclusions : Ethnic differences in prognosis exist for children with CF in South Africa and are probably related to underrecognition of CF and the socio-economic status of some patients.     

New insights into pulmonary inflammation in cystic fibrosis

Persistent lower airway infection with inflammation is the major cause of morbidity and mortality in cystic fibrosis. This review examines the recent advances in the understanding of airway inflammation in cystic fibrosis, and focuses on the evidence that pulmonary inflammation is, under some circumstances, disassociated from infection, and the potential implications for therapeutic intervention.     

Evidence for newborn screening for cystic fibrosis

Different strategies are available for studying the effectiveness of newborn screening for cystic fibrosis (CF). Although observational studies suggest clinical benefits, their results are difficult to interpret because of the potential for several methodological problems. Randomised studies show that age at time of diagnosis is an important factor in the nutritional status of pancreatically insufficient patients and that a delayed diagnosis increases the risk of malnutrition in childhood. Effects on lung disease are more controversial. Advantages other than better clinical outcome or survival may be obtained by the implementation of CF neonatal screening, mainly the opportunity for presymptomatic trials and treatments and more informed reproductive choices for parents and relatives. Disadvantages of neonatal screening for CF include the detection of heterozygotes and the discovery of mild forms of disease.     

Neonatal screening for cystic fibrosis: present and future

Despite there being effective tests for detecting cystic fibrosis (CF) using newborn screening blood samples, screening in neonates has not had universal approval because of uncertainty about its benefits. After up to 18 y experience, at a recent conference in Caen several aspects attracted universal agreement. There is still major delay in clinical diagnosis after the onset of symptoms. There is short-term benefit in early diagnosis by screening, with reduced morbidity in the first 2 y, evidence of significant nutritional benefits up to the age of 10 y, and probable respiratory benefit over this time frame. There is great potential for research into treatment modalities and no evidence of significant psychological harm to CF babies from early diagnosis. With a screening protocol that includes a DNA test there is some unwanted carrier detection and careful genetic counselling is needed. There is no evidence yet that screening will extend the life of CF patients, so some doubts remain as to its overall effectiveness, and there have been no good studies on comparative costs in screened and unscreened cohorts. Even so, the weight of evidence suggests very worthwhile advantages for screened babies and their families. Because of this, it is unlikely that further trials will take place. It may be that the onus now is on those who do not support screening to justify this stance to parents who may favour it.     

The geographic distribution of cystic fibrosis mutations gives clues about population origins

Information regarding three of the more common cystic fibrosis mutations is presented (ΔF508, G542X, N13031K) to support the concept of a geography associated with cystic fibrosis mutations. We present the hypothesis that a knowledge of the geography of cystic fibrosis mutations is important for an understanding of genotype-phenotype correlations, gene flow, historical population migration and cystic fibrosis screening. Conclusion A new method of study of mankind's cultural spread is being revealed and the survival of the various mutations supports the concept that they may provide a selective advantage to the carrier. Received: 30 June 1999 / Accepted: 15 December 1999