The need for vigilance: the case of a false-negative newborn screen for cystic fibrosis

Improved detection of cystic fibrosis by the California Newborn Screening Program for all races and ethnicities

BACKGROUND

Newborn screening (NBS) for cystic fibrosis (CF) is universal in the United States. Protocols vary but include an immunoreactive trypsinogen (IRT) level and CFTR variant panel. California CF NBS has a 3-step screening: IRT level, variant panel, and CFTR sequencing if only one variant identified on panel.

METHODS

This was a cohort study of infants with CF born in California (2007-2021) to examine racial and ethnic differences in having a false-negative NBS result for CF and at which step the false-negative occurred. We examined how different CFTR variant panels would improve detection of variants by race and ethnicity: original 39-variant panel, current 75-variant panel, and all 402 disease-causing CFTR variants in the CFTR2 database.

RESULTS

Of the 912 infants born in California with CF, 84 had a false-negative result: 38 due to low IRT level and 46 with a high IRT value (but incomplete variant detection). Asian (OR 6.3) and Black infants (OR 2.5) were more likely to have a false-negative screening result than non-Hispanic white infants. The majority of false-negative screening (but CF diagnosis) cases among American Indian/Native Alaskan and non-Hispanic White infants were due to low IRT levels. The majority of Asian and Hispanic infants with false-negative screening had no variants detected. Detection of two CFTR variants was improved with the 75-variant panel in Black, Hispanic, and non-Hispanic White infants and with the 402-variant panel in Black, Hispanic, non-Hispanic White, and other race infants.

CONCLUSIONS

Larger CFTR panels in NBS improved the detection of CF in all races and ethnicities.

Untargeted Metabolomics Identifies Biomarkers for MCADD Neonates in Dried Blood Spots

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common inherited mitochondrial metabolic disease of fatty acid β-oxidation, especially in newborns. MCADD is clinically diagnosed using Newborn Bloodspot Screening (NBS) and genetic testing. Still, these methods have limitations, such as false negatives or positives in NBS and the variants of uncertain significance in genetic testing. Thus, complementary diagnostic approaches for MCADD are needed. Recently, untargeted metabolomics has been proposed as a diagnostic approach for inherited metabolic diseases (IMDs) due to its ability to detect a wide range of metabolic alterations. We performed an untargeted metabolic profiling of dried blood spots (DBS) from MCADD newborns (n = 14) and healthy controls (n = 14) to discover potential metabolic biomarkers/pathways associated with MCADD. Extracted metabolites from DBS samples were analyzed using UPLC-QToF-MS for untargeted metabolomics analyses. Multivariate and univariate analyses were used to analyze the metabolomics data, and pathway and biomarker analyses were also performed on the significantly identified endogenous metabolites. The MCADD newborns had 1034 significantly dysregulated metabolites compared to healthy newborns (moderated t-test, no correction, p-value ≤ 0.05, FC 1.5). A total of 23 endogenous metabolites were up-regulated, while 84 endogenous metabolites were down-regulated. Pathway analyses showed phenylalanine, tyrosine, and tryptophan biosynthesis as the most affected pathways. Potential metabolic biomarkers for MCADD were PGP (a21:0/PG/F1alpha) and glutathione, with an area under the curve (AUC) of 0.949 and 0.898, respectively. PGP (a21:0/PG/F1alpha) was the first oxidized lipid in the top 15 biomarker list affected by MCADD. Additionally, glutathione was chosen to indicate oxidative stress events that could happen during fatty acid oxidation defects. Our findings suggest that MCADD newborns may have oxidative stress events as signs of the disease. However, further validations of these biomarkers are needed in future studies to ensure their accuracy and reliability as complementary markers with established MCADD markers for clinical diagnosis.

Clinical complications in children with false-negative results in cystic fibrosis newborn screening

OBJECTIVE

To present signs and symptoms and clinical course in cystic fibrosis patients with false-negative newborn screening (CF NBS).

MATERIALS AND METHODS

All children presented in this paper were covered by CF NBS. The group of 1.869.246 newborns was screened in the Institute of Mother and Child in Warsaw within a period of 01.01.1999 - 31.05.2019. Screening protocols evolved over time from IRT/IRT to IRT/DNA/EGA.

RESULTS

The authors identified 11 patients with false-negative NBS, in whom CF was diagnosed based on clinical symptoms or the examination of siblings with positive CF NBS. In the study group, the diagnosis was made significantly later in comparison to positive CF NBS patients ranging from 2 months to 15 years of age. CF NBS strategy does not significantly affect the sensitivity of the screening.

CONCLUSION

In the presence of clinical symptoms, additional diagnostics must be implemented, in spite of the negative screening results. At first, the sweat test should be conducted, followed by a DNA analysis of the most common mutations in the given population. The diagnostic process requires searching for CFTR mutations not typically associated with a high chloride concentration in sweat. Repetition of sweat chloride concentration enables the diagnosis in children whose initial chloride values in sweat are borderline, and no CF-causing mutations are detected. In strong clinical indications, the extension of DNA analysis (EGA) is recommended in order to identify rare CF variants. In children with meconium ileus, genetic analysis is mandatory.

Dehydrated patient without clinically evident cause: A case report

BACKGROUND

Patients affected by cystic fibrosis can present with metabolic alkalosis such as Bartter’s syndrome. In this case report we want to underline this differential diagnosis and we aimed focusing on the suspect of cystic fibrosis, also in case of a negative newborn screening.

CASE SUMMARY

In a hot August –with a mean environmental temperature of 36 °C– an 8-mo-old female patient presented with severe dehydration complicated by hypokalemic metabolic alkalosis, in absence of fever, diarrhea and vomiting. Differential diagnosis between cystic fibrosis and tubulopathies causing metabolic alkalosis (Bartter’s Syndrome) was considered. We started intravenous rehydration with subsequent improvement of clinical conditions and serum electrolytes normalization. We diagnosed a mild form of cystic fibrosis (heterozygous mutations: G126D and F508del in the cystic fibrosis transmembrane conductance regulator gene). The trigger factor of this condition had been heat exposure.

CONCLUSION

When facing a patient with hypokalemic metabolic alkalosis, cystic fibrosis presenting with Pseudo-Bartter’s syndrome should be considered in the differential diagnosis, even if the newborn screening was negative.

Application of Principal Component Analysis to Newborn Screening for Congenital Adrenal Hyperplasia

PURPOSE

Newborn screening laboratories are challenged to develop reporting algorithms that accurately identify babies at increased risk for congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21OHD). Screening algorithms typically use cutoff values for a key steroid(s) and include considerations for covariates, such as gestational age or birth weight, but false-positive and false-negative results are still too frequent, preventing accurate assessments. Principal component analysis (PCA) is a statistical method that reduces high-dimensional data to a small number of components, capturing patterns of association that may be relevant to the outcome of interest. To our knowledge, PCA has not been evaluated in the newborn screening setting to determine whether it can improve the positive predictive value of 21OHD screening.

METHODS

PCA was applied to a data set of 920 newborns with measured concentrations of 5 key steroids that are known to be perturbed in patients with 21OHD. A decision tree for the known outcomes (confirmed 21OHD cases and unaffected individuals) was created with 2 principal components as predictors. The effectiveness of the PCA-derived decision tree was compared with the current algorithm.

RESULTS

PCA improved the positive predictive value of 21OHD screening from 20.0% to 66.7% in a retrospective study comparing the current algorithm to a tree-based algorithm using PCA-derived variables. The streamlined PCA-derived decision tree, comprising only 3 assessment points, greatly simplified the 21OHD reporting algorithm.

CONCLUSIONS

This first report of PCA applied to newborn screening for 21OHD demonstrates enhanced detection of affected individuals within the unaffected population.

Clinical and Genotypical Features of False-Negative Patients in 26 Years of Cystic Fibrosis Neonatal Screening in Tuscany, Italy

Cystic fibrosis (CF) is a life-threatening and common genetic disorder. Cystic fibrosis newborn screening (CF NBS) has been implemented in many countries over the last 30 years, becoming a widely accepted public health strategy in economically developed countries. False-negative (FN) cases can occur after CF NBS, with the number depending on the method. We evaluated the delayed diagnosis of CF, identifying the patients who had false-negative CF NBS results over 26 years (1992–2018) in Tuscany, Italy. The introduction of DNA analysis to the newborn screening protocol improved the sensitivity of the test and reduced the FNs. Our experience showed that, overall, at least 8.7% of cases of CF received FNs (18 cases) and were diagnosed later, with an average age of 6.6 years (range: 4 months to 22 years). Respiratory symptoms and salt-loss syndrome (metabolic hypochloremic alkalosis) are suggestive symptoms of CF and were commons events in FN patients. In Tuscany, a region with a high CFTR allelic heterogeneity, the salt-loss syndrome was a common event in FNs. Therefore, we provided evidence to support the claim that the FN patients had CFTR mutations rarer compared with the true-positive cases. We underline the importance of vigilance toward clinical manifestations suggestive of CF on the part of the primary care providers and hospital physicians in a region with an efficient newborn screening program.

Newborn Screening Saves Lives but Cannot Replace the Need for Clinical Vigilance

Newborn screening for cystic fibrosis (CF) enables early diagnosis and treatment leading to improved health outcomes for patients with CF. Although the sensitivity of newborn screening is high, false-negative results can still occur which can be misleading if clinicians are not aware of the clinical presentation of CF. We present a case of a young male with negative newborn screen diagnosed for CF. He was diagnosed at 3 years of age despite having symptoms indicative of CF since infancy. The delayed diagnosis resulted in diffuse lung damage and poor growth.

False negative newborn screen and neonatal cholestasis in a premature child with cystic fibrosis

Newborn screening for cystic fibrosis enables early diagnosis and treatment, leading to better outcomes for patients with cystic fibrosis. Although the sensitivity of several screening protocols is high, false negative screening results of the newborn patient still occur, which can lead to a significant delay in diagnosis when the awareness for presenting symptoms of cystic fibrosis declines. Neonatal cholestasis is one of the presenting symptoms of cystic fibrosis but can be easily missed when total parenteral nutrition has been given. Premature newborns are probably more at risk of a missed underlying diagnosis than term babies because their co-pathologies and management are often more complex. We present a case of a 10-week-old premature boy with a false negative newborn screening for cystic fibrosis, in whom cystic fibrosis presented with neonatal cholestasis. In this case, the immunoreactive trypsinogen/pancreatitis-associated protein/35 cystic fibrosis transmembrane regulator mutation analysis/sequencing method was used. Furthermore, an overview of the literature on missed diagnosis of cystic fibrosis due to a false negative newborn screen is provided.

CONCLUSION

Cystic fibrosis (CF) should be considered in infants with neonatal cholestasis even when the newborn screening for CF is reported to be negative.

Newborn screening for cystic fibrosis

PURPOSE OF REVIEW

Newborn screening for cystic fibrosis (CF) is now universal in the US and many other countries. The rapid expansion of screening has resulted in numerous publications identifying new challenges for healthcare providers. This review provides an overview of these publications and includes ideas on managing these challenges.

RECENT FINDINGS

Most CF newborn screening algorithms involve DNA mutation analysis. As screening has expanded, new challenges have been identified related to carrier detection and inconclusive diagnoses. Early descriptions of infants with CF-related metabolic syndrome (CRMS) indicate that the natural history of this condition cannot be predicted. Early identification has also provided an opportunity to better understand the pathophysiology of CF. However, few studies have been conducted in infants with CF to determine optimal therapy and recommendations are largely anecdotal.

SUMMARY

Newborn screening provides an opportunity to identify and begin treatment early in individuals with CF. Whereas a single, optimal approach to screening does not exist, all programs can benefit from new findings regarding sweat testing, carrier detection, early pathophysiology, and clinical outcomes.