Newborn screening programmes for cystic fibrosis

Cystic fibrosis

Cystic fibrosis is a monogenic disease considered to affect at least 100 000 people worldwide. Mutations in CFTR, the gene encoding the epithelial ion channel that normally transports chloride and bicarbonate, lead to impaired mucus hydration and clearance. Classical cystic fibrosis is thus characterised by chronic pulmonary infection and inflammation, pancreatic exocrine insufficiency, male infertility, and might include several comorbidities such as cystic fibrosis-related diabetes or cystic fibrosis liver disease. This autosomal recessive disease is diagnosed in many regions following newborn screening, whereas in other regions, diagnosis is based on a group of recognised multiorgan clinical manifestations, raised sweat chloride concentrations, or CFTR mutations. Disease that is less easily diagnosed, and in some cases affecting only one organ, can be seen in the context of gene variants leading to residual protein function. Management strategies, including augmenting mucociliary clearance and aggressively treating infections, have gradually improved life expectancy for people with cystic fibrosis. However, restoration of CFTR function via new small molecule modulator drugs is transforming the disease for many patients. Clinical trial pipelines are actively exploring many other approaches, which will be increasingly needed as survival improves and as the population of adults with cystic fibrosis increases. Here, we present the current understanding of CFTR mutations, protein function, and disease pathophysiology, consider strengths and limitations of current management strategies, and look to the future of multidisciplinary care for those with cystic fibrosis.

Development of Strategies to Decrease False Positive Results in Newborn Screening

The expansion of national newborn screening (NBS) programmes has provided significant benefits in the diagnosis and early treatment of several rare, heritable conditions, preventing adverse health outcomes for most affected infants. New technological developments have enabled the implementation of testing panel covering over 50 disorders. Consequently, the increment of false positive rate has led to a high number of healthy infants recalled for expensive and often invasive additional testing, opening a debate about the harm-benefit ratio of the expanded newborn screening. The false-positive rate represents a challenge for healthcare providers working in NBS systems. Here, we give an overview on the most commonly used strategies for decreasing the adverse effects due to inconclusive screening results. The focus is on NBS performance improvement through the implementation of analytical methods, the application of new and more informative biomarkers, and by using post-analytical interpretive tools. These strategies, used as part of the NBS process, can to enhance the positive predictive value of the test and reduce the parental anxiety and healthcare costs related to the unnecessary tests and procedures.

Exploring approaches to facilitate family communication of genetic risk information after cystic fibrosis population carrier screening

Population carrier screening for cystic fibrosis (CF) enables individuals with no known family history of the condition to ascertain their risk of having a child with CF. When an individual is identified as a carrier of CF, a life-shortening condition, they are encouraged to inform their relatives who are at increased risk of being a carrier. Research suggests that the uptake of CF carrier testing amongst relatives of carriers or people with CF is low. This study aimed to explore approaches to facilitate the process of family communication of genetic information after an individual is identified as a carrier of CF through population screening. Five key informants were interviewed to inform the development of a telephone survey which was administered to 21 individuals identified as carriers of CF through population carrier screening at Victorian Clinical Genetics Services. This study suggests that providing carriers with additional information and follow-up support would be appreciated by carriers and could result in more accurate information being disseminated more widely within families, which could lead to more at-risk relatives accessing testing. Suggested strategies to enhance current practice include mailing a fact sheet to carriers and a follow-up telephone call provided by a genetic counsellor to carriers to offer further support in communicating this information to their relatives.

Establishing a diagnosis of cystic fibrosis

Cystic fibrosis (CF) is a recessively inherited condition caused by mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Characterization of the genetic defect has improved understanding of the condition and, in the majority of cases, diagnosis is straightforward. However, in a significant number, diagnosis remains a challenge. This paper will discuss the management of these issues and reflect on atypical presentations. In addition we will discuss situations in which genetic variations of the CFTR gene are not associated with a classical CF phenotype and the implications for practice in both paediatric and adult clinics.

Cystic fibrosis and neonatal screening

The clinical and diagnostic aspects of cystic fibrosis have been extensively reviewed, with an emphasis on neonatal screening. This systematic literature review involved a search for relevant contributions in the PubMed and SciELO databases. The first references to cystic fibrosis date to the Middle Ages. Cystic fibrosis is the most frequent autosomal recessive hereditary disease among Caucasians (1:2,000 to 3,500). More than 1,000 mutations lead to the disease, the most common being "F508, with 70% prevalence among Canadian, Northern European, and American Caucasians and 23 to 55% prevalence among Brazilians. The basic defect is in chloride ion secretion. Cystic fibrosis screening has long been controversial, and after almost three decades, there are few nationwide programs (most are regional or local). However, the U.S. Centers for Disease Control and Prevention (CDC) has concluded that screening for cystic fibrosis is justified. The lack of a specific screening test and the ethnic heterogeneity of the Brazilian population pose challenges for neonatal screening.

Newborn screening for cystic fibrosis: techniques and strategies

Newborn screening for cystic fibrosis has been carried out for over 25 years, and clinical and cost benefits have been documented. There is still much variation in the methods and strategies adopted. All current screening programmes use a measurement of immunoreactive trypsin as a primary screening test, and in most, a second tier test involves analysing DNA mutations. The choice of DNA mutations depends on the genetic background in the region, and considerations of cost. Using DNA analysis as part of a screening procedure has introduced unwanted carrier detection, and protocols have now been devised in an attempt to avoid this. There are at least seven distinct protocols in use, all of which have different advantages and disadvantages, and no method or strategy will suit every region. Further careful study of performance and costs of various strategies is needed.

Risk calculations for cystic fibrosis in neonatal screening by immunoreactive trypsinogen and CFTR mutation tests

PURPOSE

Although neonatal screening (or newborn screening) for cystic fibrosis (CF) is commonly practiced, systematic methods for accurate risk calculations are currently lacking.

METHODS AND RESULTS

We evaluated characteristics of the immunoreactive trypsinogen (IRT) test using the published data. The probability that a neonate has a positive IRT test, if the neonate is affected, a carrier, or a noncarrier, is approximately 1, 0.041, or 0.011, respectively. We provide methods to calculate genetic risks for a variety of commonly encountered scenarios in which neonates are positive by the IRT test.

CONCLUSION

Our Bayesian methods permit CF disease probabilities to be calculated accurately, taking into account all relevant information.

Sweat-testing in preterm and full-term infants less than 6 weeks of age

Our objective was to examine the characteristics of preterm and full-term infants < or = 6 weeks old that influence the success of obtaining sufficient sweat for diagnosis of CF, and corresponding sweat chloride concentrations. A retrospective chart review of 119 sweat tests was performed on 103 preterm and full-term infants < or = 6 weeks of age. Bivariate and multivariate regression analyses were used to determine the predictors of successful sweat testing and characteristics influencing sweat chloride concentrations. Adequate amounts of sweat (> or = 75 mg) were obtained for analysis in 73.8% of initial attempts in the infant group. The following characteristics were associated with increased odds of obtaining a quantity not sufficient (QNS) for sweat chloride concentration measurement: African-American race, infant weight < 2,000 g, preterm birth, and postmenstrual age (PMA) < 36 weeks. With a multivariable logistic model, the only significant predictors were African-American race (7.3, 2.4-21.7) and PMA < 36 weeks (17.9, 4.2-75.9). Sweat chloride concentration in non-CF individuals is inversely related to both gestational age and age at testing, and this effect is additive in a linear regression model. In conclusion, sweat collection can be reliably performed in infants > or = 36 weeks postmenstrual age, > 2,000 g, and > 3 days postnatal age. Maturational factors have a mild impact on sweat chloride concentration.

Genotyping single nucleotide polymorphisms by MALDI mass spectrometry in clinical applications

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry has become one of the most powerful and widely applied technologies for SNP scoring and determination of allele frequencies in the post-genome sequencing era. Although different strategies for allele discrimination combined with MALDI were devised, in practice only primer extension methods are nowadays routinely used. This combination enables the rapid, quantitative, and direct detection of several genetic markers simultaneously in a broad variety of biological samples. In the field of molecular diagnostics, MALDI has been applied to the discovery of genetic markers, that are associated with a phenotype like a disease susceptibility or drug response, as well as an alternative means for diagnostic testing of a range of diseases for which the responsible mutations are already known. It is one of the first techniques with which whole genome scans based on single nucleotide polymorphisms were carried out. It is equally well suited for pathogen identification and the detection of emerging mutant strains as well as for the characterization of the genetic identity and quantitative trait loci mapping in farm animals. MALDI can also be used as a detection platform for a range of novel applications that are more demanding than standard SNP genotyping such as mutation/polymorphism discovery, molecular haplotyping, analysis of DNA methylation, and expression profiling. This review gives an introduction to the application of mass spectrometry for DNA analysis, and provides an overview of most studies using SNPs as genetic markers and MALDI mass spectrometric detection that are related to clinical applications and molecular diagnostics. Further, it aims to show specialized applications that might lead to diagnostic applications in the future. It does not speculate on whether this methodology will ever reach the diagnostic market.

Update on newborn screening for cystic fibrosis

PURPOSE OF REVIEW

Cystic fibrosis (CF) is the most common lethal genetic disorder in the United States to be identified in childhood. In November 2003 the US Cystic Fibrosis Foundation and the Centers for Disease Control and Prevention convened an expert panel to review the indications for CF newborn screening. In this review we discuss the information during the year leading up to this meeting as well as publications since the meeting.

RECENT FINDINGS

During the past several years an increasing number of CF patients have been diagnosed with newborn screening. These patients have demonstrated several benefits to screening while also uncovering new challenges. Health benefits have included improved nutrition persisting for many years and the avoidance of nutritional complications. Early identification has also meant that these often clinically healthy infants are being followed in CF centers for care. This has added to the need for avoiding infection risks to which these patients might not have otherwise been exposed. Psychosocial benefits include the avoidance of stress due to delayed diagnosis as well as assistance with family planning. Psychosocial challenges include carrier identification and detection of patients with mild disease or without a clear diagnosis.

SUMMARY

Although no study has definitively shown reduced lung disease or prolonged survival in CF patients detected by newborn screening, the general consensus is that improved nutrition and cognitive potential, in addition to the reduced costs for hospitalization and intensive therapies, support the benefits of screening.

Should children and adolescents undergo genetic testing?

Genetic testing comes in many shapes and sizes. The decision to undergo genetic testing must involve consideration of the medical, psychosocial, and reproductive benefits and risks of testing. The evaluation of risks and benefits varies significantly both between and within families. Pediatricians should keep up with the rapid advances in genetic medicine and the myriad of tests that are being developed and marketed. They also need to be familiar with the psychosocial risks and benefits that these new tests generate for individuals, families and communities. In some situations, genetic testing is merely another diagnostic tool; in other situations, genetic testing offers information about the risks for future diseases. Pediatricians need to be knowledgeable about tests that are indicated clinically and their potential psychosocial implications to best serve children, adolescents, and their families.

Early intervention and prevention of lung disease in cystic fibrosis: a European consensus

In patients with cystic fibrosis (CF), early intervention and prevention of lung disease is of paramount importance. Principles to achieve this aim include early diagnosis of CF, regular monitoring of the clinical status, various hygienic measures to prevent infection and cross-infection, early use of antibiotic courses in patients with recurrent or continuous bacterial colonisation and appropriate use of chest physiotherapy.