Different Viewpoints: International Perspectives on Newborn Screening

Newborn Screening: Review of its Impact for Cystinosis

Newborn screening (NBS) programmes are considered to be one of the most successful secondary prevention measures in childhood to prevent or reduce morbidity and/or mortality via early disease identification and subsequent initiation of therapy. However, while many rare diseases can now be detected at an early stage using appropriate diagnostics, the introduction of a new target disease requires a detailed analysis of the entire screening process, including a robust scientific background, analytics, information technology, and logistics. In addition, ethics, financing, and the required medical measures need to be considered to allow the benefits of screening to be evaluated at a higher level than its potential harm. Infantile nephropathic cystinosis (INC) is a very rare lysosomal metabolic disorder. With the introduction of cysteamine therapy in the early 1980s and the possibility of renal replacement therapy in infancy, patients with cystinosis can now reach adulthood. Early diagnosis of cystinosis remains important as this enables initiation of cysteamine at the earliest opportunity to support renal and patient survival. Using molecular technologies, the feasibility of screening for cystinosis has been demonstrated in a pilot project. This review aims to provide insight into NBS and discuss its importance for nephropathic cystinosis using molecular technologies.

It All Depends What You Count-The Importance of Definitions in Evaluation of CF Screening Performance

Screening metrics are essential to both quality assessment and improvement, but are highly dependent on the way positive tests and cases are counted. In cystic fibrosis (CF) screening, key factors include how mild cases of late-presenting CF and CF screen positive, inconclusive diagnosis (CFSPID) are counted, whether those at prior increased risk of CF are excluded from the screened population, and which aspects of the screening pathway are considered. This paper draws on the New Zealand experience of almost forty years of newborn screening for CF. We demonstrate how different definitions impact the calculation of screening sensitivity. We suggest that, to enable meaningful comparison, CF screening reports should clarify what steps in the screening pathway are included in the assessment, as well as the algorithm used and screening target.

Prenatal Screening Markers for Down Syndrome: Sensitivity, Specificity, Positive and Negative Expected Value Method

Background

Genetic screening for chromosomopathy is performed in the first trimester of pregnancy by determining fetal nuchal translucency (NT), and the pregnancy associated plasma protein-A (PAPP-A) and free human chorionic gonadotropin (free-beta HCG) biomarkers in maternal serum.

Methods

We tested the sensitivity, specificity, positive and negative expected values of each marker with the aim of setting a model for prenatal screening readings. Statistical data treatment has been performed on a sample of 340 pregnant women with positive results of prenatal screening.

Results

Sensitivity of PAPP-A was 0.6250 (probability 62.50%), free beta HCG 0.5893 (58.93%), NT 0.1785 (17.85%). Specificity of PAPP-A was 0.5106 (probability 51.06%), free beta HCG 0.5246 (52.46%), NT 0.9718 (97.18%). Positive expected value of PAPP-A was 0.2011 (probability 20.11%), free beta HCG 0.1964 (19.64%), NT 0.556 (55.56%). Negative expected value of PAPP-A was 0.8735 (probability 87.35%), free beta HCG 0.8662 (86.62%), NT 0.8571 (85.71%). The NT marker has a significantly higher specificity, which means that its normal value will significantly reduce the final risk of trisomy 21. The sensitivity of NT is much lower than that of biochemical markers, which means that a pathological value of NT does not have a significant influence on the final risk, i.e. the significantly higher sensitivity of biochemical markers will reduce the final risk of trisomy 21.

Conclusions

The analyses stress the importance of using a software which has the possibility to separate the level of a biochemical risk by correlating PAPP-A and free beta HCG and, by adding the NT marker, calculate the level of a final risk of Down syndrome.

Comparison of Spectrophotometric and Fluorimetric Methods in Evaluation of Biotinidase Deficiency

Background

Biotin, a water-soluble vitamin, is used as a co-factor by enzymes involved in carboxylation reactions. Biotinidase (BTD) catalyzes the recycling of biotin from endogenous and dietary sources. Biotinidase deficiency (BD) is an autosomal recessively inherited disorder of biotin recycling that is associated with neurologic and cutaneous consequences when untreated. The aim of the study was to compare the results of spectrophotometric and fluorimetric methods, as well as to evaluate the advantages and disadvantages of both methods in current research practices.

Methods

Study group was chosen among the BD suspected newborn, children and parents (n = 52) who applied to Hacettepe University Pediatric Metabolism Unit.

Results

BTD activity is stable for 2 hours at room temperature and at 4 °C, and for 4 months at –20 °C and –80 °C. Genetic and clinical results showed that 25% of the total number of patients had complete BD which was treated with 10 mg/day biotin, while 15.38% of the patients had partial BD, and they were prescribed biotin 5 mg/day. The area under the ROC curve was 0.960±0.25 and 0.927± 0.41 for the fluorimetric and spectrophotometric method, respectively. Fluorimetric method showed 100% sensitivity and 97% specificity, whereas spectrophotometric method showed 90.5% sensitivity and 93.7% specificity.

Conclusions

Fluorimetric method is superior to the spectrophotometric method due to higher sensitivity and specificity.