Measuring free thyroxine levels in neonatal heel-prick samples

The Dutch neonatal screening scheme for Congenital Hypothyroidism (CH) is primarily based on the determination of thyroxine (T4) in filter paper blood spots. In the lowest 5% of T4 values, thyroxine binding globulin (TBG) is measured in order to be able to correct for occasional low TBG levels. However, because the commercial TBG kit has been withdrawn from the market, alternative strategies are needed to be explored including the assessment of free T4. We evaluated the Neonatal Free Thyroxine (fT4) enzyme immunoassay (EIA) kit of Bio-Rad. FT4 as measured in a daily run of random samples correlated with T4. We also observed a correlation between fT4 and T4, and between fT4 and T4/TBG ratio in blood spots with low T4 concentrations. The correlation between fT4 and T4 in blood spots of proven CH-patients was highly significant. ROC curves were constructed for the fT4 assay and the T4/TBG ratio based on 27 CH patients and 215 controls with a complete set of data. The curves of both assays seemed to be rather similar. We conclude that the validity of the fT4 and the T4/TBG-approach seems to be the same. A study with a larger sample size giving the same or even more favorable results for the fT4-approach is necessary before we will change the present CH protocol.

The influence of sex, gestational age, birth weight, blood transfusion, and timing of the heel prick on the pancreatitis-associated protein concentration in newborn screening for cystic fibrosis

BACKGROUND

Pancreatitis-associated protein (PAP) is currently discussed as a marker in newborn screening (NBS) for cystic fibrosis (CF). However, it is not known if PAP concentrations are influenced by sex, gestational age, birth weight, blood transfusion or time of collection and what this would mean for NBS for CF.

METHODS

In 2008 all newborns in part of the Netherlands were screened for CF by an IRT/PAP protocol. PAP concentration was determined by the MucoPAP ELISA (DynaBio), which was modified to a Dissociation Enhanced Lanthanide Fluoroimmunoassay (DELFIA) method following a protocol of PerkinElmer.

RESULTS

In healthy newborns, the median PAP concentration was 0.5 μg/l (Interquartile range (IQR 0.3-0.8) whereas this was 3.2 μg/l (IQR 2.0-12.5) in CF infants. PAP concentrations were lower in premature infants 0.94 and 0.91 times for 25 to 31 + 6 weeks GA and 32 to 36 + 6 weeks respectively. A higher PAP concentration was observed in low-birth-weight infants (<2500 gram)(p = 0.001), per 100 gram birth weight gained the PAP concentration decreased with 0.1 %. PAP levels were higher after a blood transfusion, the 95th percentile increased from 1.3 to 3.6 μg/l leading to a higher false-positive rate. The PAP concentration increased when newborn screening was performed more than 168 hours (day 7) after birth (β = 1.63), the 95th percentile increased from 1.3-1.6 μg/l to 4.0 μg/l after 168 hours (72,874 newborns were screened).

CONCLUSION

Sex, birth weight, and gestational age lead to small differences in PAP concentrations without consequences for the screening algorithm. However, blood transfusion as well as performance of the heel prick after 168 hours (7 days) lead to clinically significant higher PAP levels and to a higher risk on a false-positive screening test result.

Risk stratification by residual enzyme activity after newborn screening for medium-chain acyl-CoA dehyrogenase deficiency: data from a cohort study

Background

Since the introduction of medium-chain acyl coenzyme A dehydrogenase (MCAD) deficiency in population newborn bloodspot screening (NBS) programs, subjects have been identified with variant ACADM (gene encoding MCAD enzyme) genotypes that have never been identified in clinically ascertained patients. It could be hypothesised that residual MCAD enzyme activity can contribute in risk stratification of subjects with variant ACADM genotypes.

Methods

We performed a retrospective cohort study of all patients identified upon population NBS for MCAD deficiency in the Netherlands between 2007–2010. Clinical, molecular, and enzymatic data were integrated.

Results

Eighty-four patients from 76 families were identified. Twenty-two percent of the subjects had a variant ACADM genotype. In patients with classical ACADM genotypes, residual MCAD enzyme activity was significantly lower (median 0%, range 0-8%) when compared to subjects with variant ACADM genotypes (range 0-63%; 4 cases with 0%, remainder 20-63%). Patients with (fatal) neonatal presentations before diagnosis displayed residual MCAD enzyme activities <1%. After diagnosis and initiation of treatment, residual MCAD enzyme activities <10% were associated with an increased risk of hypoglycaemia and carnitine supplementation. The prevalence of MCAD deficiency upon screening was 1/8,750 (95% CI 1/7,210–1/11,130).

Conclusions

Determination of residual MCAD enzyme activity improves our understanding of variant ACADM genotypes and may contribute to risk stratification. Subjects with variant ACADM genotypes and residual MCAD enzyme activities <10% should be considered to have the same risks as patients with classical ACADM genotypes. Parental instructions and an emergency regimen will remain principles of the treatment in any type of MCAD deficiency, as the effect of intercurrent illness on residual MCAD enzyme activity remains uncertain. There are, however, arguments in favour of abandoning the general advice to avoid prolonged fasting in subjects with variant ACADM genotypes and >10% residual MCAD enzyme activity.

The Proline/Citrulline Ratio as a Biomarker for OAT Deficiency in Early Infancy

Deficiency of ornithine-δ-aminotransferase (OAT) in humans results in gyrate atrophy. Early diagnosis may allow initiation of treatment before irreversible damage has occurred. However, diagnosis is commonly delayed well into adulthood because of the nonspecific character of initial symptoms. Here, we report findings in a neonate who was evaluated because of a positive family history of OAT deficiency. The reversed enzymatic flux in early infancy resulted in borderline low ornithine concentration - evoking urea cycle disturbances - and increased proline. In addition, plasma citrulline was low. Consequently, the proline/citrulline ratio in plasma was increased compared to controls. To find out whether amino acid profiling in neonatal dried blood spots is suitable to detect OAT deficiency, we evaluated the original newborn dried blood spots of two affected patients and compared it with a database of >450,000 newborns tested in Minnesota since 2004. Proline concentrations (777 and 1,381 μmol/L) were above the 99 percentile (776 μmol/L) of the general population, and citrulline concentrations (4.5 and 4.9 μmol/L) only just above the 1 percentile (4.37 μmol/L). The proline/citrulline ratio was 172.9 and 281.8, respectively. This ratio was calculated retrospectively in the normal population, and the 99 percentile was 97.6. Applying this ratio for NBS could lead to early and specific detection of neonatal OAT deficiency, with no additional expense to newborn screening laboratories quantifying amino acids. Given that early diagnosis of OAT disease can lead to earlier treatment and prevent visual impairment, further studies are indicated to evaluate whether newborn screening for OAT deficiency is warranted.

Implementing neonatal screening for haemoglobinopathies in the Netherlands

BACKGROUND

The birth prevalence of severe haemoglobinopathies such as sickle cell disease (SCD) in the Netherlands has been estimated to be at least 50 newborns per year. Neonatal screening for SCD was added to the Dutch screening programme in January 2007. We here evaluated three high performance liquid chromatography (HPLC) systems for application in neonatal screening for haemoglobinopathies, and present the results of a subsequent pilot screening programme.

METHODS

The Variant NewBorn Screening (Vnbs) HPLC system (Bio-Rad) was validated by analysing 131 blood samples and blood mixtures. Subsequently, the performance of the G7 (Tosoh BioScience) and Ultra (Primus Corporation) was compared with the Vnbs. The three HPLC analysers were tested in a pilot screening programme on 21,969 dried blood spot samples from the routine Dutch neonatal screening programme.

RESULTS

The pilot screening resulted in 188 abnormal patterns. The three HPLC devices presented comparable within- and between-run precision and detected the abnormal samples similarly. The high throughput, sampling systems, presentation of results, and integration of the chromatograms, however, were different.

CONCLUSION

All three analysers detected the same abnormal haemoglobins satisfactorily, but integrated the chromatograms with variable imprecision. Comparison of the results suggested that the Bio-Rad Vnbs was the preferred system. However, software adjustments were required to improve the diagnostic potential of this device for screening for beta- and alpha-thalassaemia.

Newborn screening for congenital adrenal hyperplasia in the Netherlands

OBJECTIVE

To evaluate whether congenital adrenal hyperplasia (CAH) patients can be detected by newborn screening before the occurrence of life-threatening salt wasting and whether the prevalence, specificity, and sensitivity are adequate enough for a routine screening procedure.

DESIGN

From 1998, a 2-year regional pilot screening for CAH was performed. In 1998, cutoff levels for 17OHP were primarily based on birth weight, and in 1999 on gestational age. In addition, nationwide, all newly diagnosed patients with CAH were reported to the Dutch Pediatric Surveillance Unit to compare screened CAH patients with CAH patients in the area without screening.

RESULTS

In 2 years, 176 684 newborns were screened and 15 CAH patients (7 males/8 females) were detected. Therapy was started at the median age of 7 days. In the area without screening, 223 307 infants were born and 19 CAH patients (10 males/9 females) were reported to the Dutch Pediatric Surveillance Unit. Therapy was started at the median age of 14 days. The mean (standard deviation) serum sodium concentration was 134.5 (3.4) mmol/L in the area of screening versus 124.5 (10.8) mmol/L in the area without screening. The overall prevalence was 1:11 764. In 1998 and 1999, the specificity was 99.76% and 99.97%, respectively. The positive predictive value was 4.5% and 16%, respectively. To date, no false-negative cases have been detected.

CONCLUSION

Severe salt wasting can be prevented by neonatal screening. The prevalence, specificity, and sensitivity allowed addition of screening for CAH to the routinely performed national neonatal screening program.

Hormonal status and the neuroendocrine response to a novel heterotypic stressor involving subchronic noise exposure

Despite a number of studies on noise-induced health effects, it is still unclear to what extent different neuroendocrine pathways are affected by noise exposure. Male Wistar rats were housed in sound-attenuated rooms isolated for noise from outside. Three groups of chronically cannulated rats were exposed to either background noise (+/-64 dB) only or irregular experimental white noise (90 dB, 2-22 kHz). Two protocols, with approximately the same total amount of noise but with different densities, were used: protocol N1 (180 min random noise per day for 18 days) or protocol N2 (540 min random noise per day for 8 days). Basal levels of circulating hormones (ACTH, corticosterone, prolactin and catecholamines) and plasma glucose were measured. In control animals, no significant changes in any of these parameters were observed over 18 days. Except for plasma prolactin, N1 did not induce a significant elevation in basal hormonal levels. N2 however induced significant elevation in basal prolactin, corticosterone and noradrenaline levels. At the end of the exposure period, all animals were subjected to a novel heterotypic stressor (restraint stress) to monitor differences in neuroendocrine activation (ACTH, corticosterone and prolactin). Compared to nonexposed control animals, N1 animals showed a normal ACTH and an enhanced corticosterone response, whereas N2 animals showed an increased ACTH but a normal corticosterone response. The prolactin response of both N1 and N2 animals was significantly decreased. Adrenal cell suspension experiments revealed that in noise-exposed rats both basal- and ACTH-stimulated corticosterone production were significantly increased as compared to control animals. These results indicate that chronic noise exposure at mild intensities induces subtle but significant changes in hormonal regulation.

Effect of hormone depletion on cell survival in the EMR-86 rat mammary carcinoma

Growth of the transplantable EMR-86 rat mammary carcinoma depends on elevated prolactin levels which are induced by oestrogenic stimulation of the pituitary. We investigated histological and cell kinetic changes during tumour regression after removal of implanted oestrogen pellets (EP), and we especially focused on the role of apoptosis. After EP removal, serum prolactin decreased to basal levels in 5 days, reaching its largest depletion during the first day. Similarly, S-phase cell fractions, assessed by bromodeoxyuridine (BrdUrd) incorporation, decreased to half the initial value during the first day and developed into a gradual decrease to basal levels thereafter. Within 10 days, tumour volumes were reduced to 20% without striking changes in tissue architecture. To quantify apoptosis, we applied a method that stains DNA breaks in tissue sections and subsequently measured the stained area by automated image cytometry. This procedure was necessary, as the subtle changes could not be detected by histological examination alone. One day after the rapid decline of the S-phase fraction, a 3-fold increase in apoptotic area was observed that remained for about 3 days and then gradually decreased. This correlated with the histologically observed reduction of tumour cells. In spite of the major cell loss, regression came to a halt after about 10 days. The surviving cell fraction is discussed within the context of a stem cell hypothesis, in which tumour cells with stem cell characteristics are less susceptible to hormone-induced apoptosis than their (non-stem) daughter cells. This notion has implications for the eradication of residual tumour cells, because a diminished susceptibility might also apply to apoptosis induced by radio- or chemotherapy.

Effects of subcutaneous versus intravenous administration of cyclosporin A on rat thymic histology and pharmacokinetics

Cyclosporin A (CsA) was administered to rats by repeated subcutaneous (s.c.) or intravenous (i.v.) injections for 14 days. Changes in thymic histology were independent of the route of administration. Blood concentration--time profiles of CsA were similar at dose levels of i.v. 7.5 and s.c. 15 mg/kg/day, respectively. So, provided that the dose is reduced, i.v. injection can serve as an adequate alternative to s.c. injection, thereby preventing unwanted painful side-effects associated with the latter route of administration.