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.

Comparison of different IRT-PAP protocols to screen newborns for cystic fibrosis in three central European populations

BACKGROUND

In recent years different IRT/PAP protocols have been evaluated, but the individual performance remains unclear. To optimize the IRT/PAP strategy we compared protocols from three regional CF newborn screening centers (Heidelberg, Dresden, and Prague).

METHODS

We evaluated the effect of elevating the IRT-cut-off from 50 to 65 μg/l (~97.5th to ~99.0th percentile), the need of a failsafe protocol (FS, IRT ≥ 99.9th percentile) and the relative performance using either two IRT-dependent PAP-cut-offs or one PAP-cut-off.

FINDINGS

Elevation of the IRT cut-off to 65 μg/l (~99.0th percentile) increased the PPV significantly (Dresden: 0.065 vs. 0.080, p < 0.0001, Prague: 0.052 vs. 0.074, p < 0.0001) without reducing sensitivity. All three IRT/PAP protocols showed a trend towards a higher sensitivity with FS than without and when using one PAP-cut-off instead of two IRT-dependent PAP-cut-offs.

CONCLUSIONS

For best performance we suggest an IRT/PAP protocol with an IRT-cut-off close to the 99.0th percentile, FS, and a single PAP-cut-off.

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.

Effects of Valproate on Acylcarnitines in Children with Epilepsy Using ESI-MS/MS

PURPOSE

To determine the influence of valproate (VPA) treatment on acylcarnitines in children with epilepsy.

METHODS

Determination of acylcarnitines (including free carnitine and acylcarnitines from C2 to C18) in dried blood spot specimens using tandem-mass spectrometry. Longitudinal study of changes in acylcarnitines in children under VPA treatment without pretreatment (group 1) or with pretreatment with other antiepileptic drugs (group 2) before the start of VPA treatment at an early and a late treatment interval (12-66, 90-260 days after the beginning of treatment, respectively). Cross-sectional comparison of these two VPA groups and of a group receiving carbamazepine monotherapy (group 3) with controls.

RESULTS

Acylcarnitines in epileptic patients before VPA therapy did not differ from control values. In group 1, decreases of C0 (-26%), C2 (-12%), C16 (-31%), C18 (-41%), C(total) (-10%), increases of C5OH (+31%), C8 (+33%) in the early treatment interval, and decreases of C16 (-21%), C18 (-42%), and increases of C2 (+26%), C5OH (+44%) in the late treatment interval were significant. In group 2, both in the longitudinal and the cross-sectional study, only a decrease of C18 (-41%, -43%, respectively) in the late treatment interval was found. In group 3, no significant changes have been observed.

CONCLUSIONS

We could prove changes in acylcarnitine subspecies, which were associated with VPA treatment in children with epilepsy. The treatment interval with the most marked changes coincides with the interval of highest risk for VPA-induced hepatotoxicity. The observed specific acylcarnitine pattern might point to the impaired intermediary metabolism that is responsible for VPA-induced hepatotoxicity.

Measurement of bile acid CoA esters by high-performance liquid chromatography-electrospray ionisation tandem mass spectrometry (HPLC-ESI-MS/MS)

The novel and rapid assay presented here combines high-performance liquid chromatography and electrospray ionisation tandem mass spectrometry (HPLC-ESI-MS/MS) to directly measure and quantify the CoA esters of 3alpha,7alpha,12alpha-trihydroxy- and 3alpha,7alpha-dihydroxy-5beta-cholestan-26-oic acid (THCA and DHCA). The latter are converted inside peroxisomes to the primary bile acids, cholic and chenodeoxycholic acids, respectively. Prior to MS/MS, esters were separated by reversed-phase HPLC on a C(18) column using an isocratic mobile phase (acetonitrile/water/2-propanol) and subsequently detected by multiple reaction monitoring. For quantification, the CoA ester of deuterium-labelled 3alpha,7alpha,12alpha-trihydroxy-5beta-cholan-24-oic acid (d(4)-CA) was used as internal standard. To complete an assay took less than 8 min. To verify the validity of the assay, the effect of peroxisomal proteins on the efficacy of extraction of the CoA esters was tested. To this end, variable amounts of the CoA esters were spiked with a fixed amount of either intact peroxisomes or peroxisomal matrix proteins and then extracted using a solid-phase extraction system. The CoA esters could be reproducibly recovered in the range of 0.1-4 micromol l(-1) (linear correlation coefficient R(2) > 0.99), with a detection limit of 0.1 micromol l(-1). In summary, electrospray ionization tandem mass spectrometry combined with HPLC as described here proved to be a rapid and versatile technique for the determination of bile acid CoA esters in a mixture with peroxisomal proteins. This suggests this technique to become a valuable tool in studies dealing with the multi-step biosynthesis of bile acids and its disturbances in disorders like the Zellweger syndrome.

Acylcarnitine profiles of preterm infants over the first four weeks of life

Measurement of free carnitine and acylcarnitines allows the detection of several inborn errors of metabolism in neonatal screening. Because available data for premature infants is limited, we studied longitudinal changes in acylcarnitine profiles of full-term and preterm neonates over the first 4 weeks of life. One hundred twenty infants were divided into four groups of 30: A, gestational age 22 to 27 wk; B, 28 to 31 wk; C, 32 to 36 wk; and D, 37 to 41 wk. Blood samples spotted on a Guthrie card were taken on days 5 and 28. Additional specimens (groups A and B only) were collected on days 1, 3, 7, and 14. Carnitine and its acyl esters were detected by looking for the precursor ions of m/z = 85 using a PE Sciex API 365 electrospray ionization tandem mass spectrometer. Concentrations of free carnitine and most acylcarnitines were significantly higher in group A compared with group D postnatally. Groups B and C displayed intermediate values. Carnitine levels in infants from group A and B decreased steadily from day 1 to day 7, and recovered up to day 14 in group B only. On day 28 carnitine concentrations had further decreased in group A, while reaching postnatal levels again in group B. Postnatal carnitine levels are higher in very immature preterm infants compared with full-term infants, but become lower on day 28. However, the commonly used metabolite ratios should still allow the detection of inborn errors of metabolism.

Postnatal changes in neonatal acylcarnitine profile

++Electrospray-tandem mass spectrometry represents a powerful method for detection of inborn errors of fatty acid metabolism. In the present study, it was used to examine neonatal carnitine metabolism, which reflects fatty acid metabolism. In 70 healthy neonates, blood samples were taken from the umbilical cord and by heel-stick puncture in full-term neonates on postnatal d 5. Cord blood specimens were also obtained from 15 preterm and 10 small-for-gestational-age infants. Acylcarnitine concentrations were measured in dried blood spots by electrospray tandem mass spectrometry. Compared with cord blood, the levels of nearly all acylcarnitine species were significantly higher on the postnatal d 5, whereas free carnitine remained unchanged. Total acylcarnitine/free carnitine-ratio increased, whereas the free carnitine/total carnitine-ratio (0.54 +/- 0.05; p < 0.01) further decreased. A reduced availability of free carnitine in the early neonatal period may affect fatty acid oxidation and thus be of potential pathophysiological relevance under conditions with higher energy demands, e.g. in sepsis. Cord blood concentrations of free carnitine, total carnitine, and total acylcarnitines were strongly related to birth weight (p < 0.01). Lower umbilical artery pH, i.e. mild hypoxia, caused accumulation of mainly long-chain acylcarnitines. This implicates that long-chain acylcarnitines could serve as a parameter of perinatal asphyxia.

Mild trimethylaminuria caused by common variants in FMO3 gene

Mild to transient trimethylaminuria is caused by common variants in the FMO3 gene leading to greatly reduced enzyme activity in vivo. FMO3 deficiency may have clinical relevance well beyond unpleasant body odour.

Sensitivity of electrospray-tandem mass spectrometry using the phenylalanine/tyrosine-ratio for differential diagnosis of hyperphenylalaninemia in neonates

The sensitivity of amino acid analysis by electrospray-tandem mass spectrometry (ESI-TMS) in differential diagnosis of the different forms of hyperphenylalaniemias (HPA) was studied in a total number of 78 dried blood samples from neonates with increased phenylalanine (Phe) concentrations (> 150 micromol/l). Simultaneous quantitative analysis of Phe and tyrosine (Tyr) were performed by ESI-TMS. By means of the Phe/Tyr-ratio it was possible to differentiate between phenylketonuria (PKU; n = 23) and nonPKU-HPA patients (n = 35; P < 0.001) with a sensitivity of 100%. Neonates with transient HPA (n = 9) showed a lower Phe/Tyr-ratio compared to the nonPKU-HPA patients (P < 0.001). Amino acid analysis by ESI-TMS represents a powerful diagnostic tool in differential diagnosis of HPA and is an appropriate technique in the setting of neonatal screening based on dried blood spots.