Veronica Wiley

Outcome of neonatal screening for medium-chain acyl-CoA dehydrogenase deficiency in Australia: a cohort study

BACKGROUND Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the disorder thought most to justify neonatal screening by tandem-mass spectrometry because, without screening, there seems to be substantial morbidity and mortality. Our aim was to assess the overall effectiveness of neonatal screening for MCAD deficiency in Australia. METHODS We identified MCAD-deficient patients from a total population of 2,495,000 Australian neonates (810,000 screened) born between April 1, 1994, and March 31, 2004. Those from a cohort of 1,995,000 (460,000 screened) were followed up for at least 4 years, and we recorded number of deaths and severe episodes, medical and neuropsychological outcome, and hospital admissions within the screened and unscreened groups. FINDINGS In cohorts aged at least 4 years there were 35 MCAD-deficient patients in those not screened (2.28 per 100,000 total population) and 24 in the screened population (5.2 per 100,000). We estimated that patients with this disorder in the unscreened cohort remained undiagnosed. Before 4 years of age, three screened patients had an episode of severe decompensation (including one neonatal death) versus 23 unscreened patients (including five deaths). At the most conservative estimate, relative risk of an adverse event was 0.44 (95% CI 0.13-1.45). In the larger cohort the relative risk (screened vs unscreened) of an adverse event by age 2 years was 0.26 (95% CI 0.07-0.97), also a conservative estimate. 38 of 52 living patients had neuropsychological testing, with no suggestions of significant differences in general cognitive outcome between the groups. INTERPRETATION Screening is effective in patients with MCAD deficiency since early diagnosis reduces deaths and severe adverse events in children up to the age of 4 years.

Neonatal screening for cystic fibrosis: A comparison of two strategies for case detection in 1.2 million babies

OBJECTIVES To review the overall performance of a neonatal screening program for cystic fibrosis (CF) from 1981 to 1994, and to compare two strategies of case detection. PROGRAM DESIGN Initially, immunoreactive trypsin (IRT) was measured in dried blood spots, and because of the low sensitivity of this test at days 3 to 5, a second sample was needed from babies with positive test results. Since 1993 a positive IRT assay result has been followed by direct gene analysis for the common CF mutation, delta F508, with the use of the same sample. Cases with false-negative results were actively sought throughout the period. RESULTS With IRT alone, 1,015,000 babies were tested. Of 389 babies with CF, 30 had a clinical diagnosis of CF made after a negative screening test result or an administrative error. Early diagnosis was achieved in 92%. With the IRT/DNA protocol, 59 of 62 infants had a positive screening test result (44 were homozygous for delta F508) among 189,000 babies tested. Three babies with CF had no copy of this mutation, but two were identified early because of meconium ileus. The false-positive rate was much greater for IRT alone than for the IRT/DNA test (0.69% vs 0.054%). All false-positive cases in the IRT/DNA protocol were, of necessity, CF carriers. CONCLUSION The percentage of babies with CF who had an early diagnosis was similar with the two protocols, but we concluded that the advantages of the IRT/DNA test for screening, particularly in the avoidance of the need for second IRT samples, outweighed the drawback of unwanted carrier detection.

Expanded newborn screening: Outcome in screened and unscreened patients at age 6 years

OBJECTIVE: Tandem mass spectrometry is widely applied to routine newborn screening but there are no long-term studies of outcome. We studied the clinical outcome at six years of age in Australia. METHODS: In a cohort study, we analyzed the outcome at 6 years for patients detected by screening or by clinical diagnosis among >2 million infants born from 1994 to 1998 (1 017 800, all unscreened) and 1998 to 2002 (461 500 screened, 533 400 unscreened) recording intellectual and physical condition, school placement, other medical problems, growth, treatment, diet, and hospital admissions. Results were analyzed separately for medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and other disorders, and grouped patients as those who presented clinically or died in the first 5 days of life; patients presented later or diagnosed by screening, and those with substantially benign disorders. RESULTS: Inborn errors, excluding phenylketonuria, were diagnosed in 116 of 1 551 200 unscreened infants (7.5/100 000 births) and 70 of 461 500 screened infants (15.2/100 000 births). Excluding MCADD, 21 unscreened patients with metabolic disorders diagnosed after 5 days of life died or had a significant intellectual or physical handicap (1.35/100 000 population) compared with 2 of the screened cohort (0.43/100 000; odds ratio: 3.1 [95% CI: 0.73–13.32]). Considering the likely morbidity or mortality among the expected number of never-diagnosed unscreened patients, there would be a significant difference. Growth distribution was normal in all cohorts. CONCLUSION: Screening by tandem mass spectrometry provides a better outcome for patients at 6 years of age, with fewer deaths and fewer clinically significant disabilities.

Application of tandem mass spectrometry to biochemical genetics and newborn screening

Tandem mass spectrometry (MS/MS) has become a key technology in the fields of biochemical genetics and newborn screening. The development of electrospray ionisation (ESI) and associated automation of sample handling and data manipulation have allowed the introduction of expanded newborn screening for disorders which feature accumulation of acylcarnitines and certain amino acids in a number of programs worldwide. In addition, the technique has proven valuable in several areas of biochemical genetics including quantification of carnitine and acylcarnitines, in vitro studies of metabolic pathways (in particular beta-oxidation), and diagnosis of peroxisomal and lysosomal disorders. This review covers some of the basic theory of MS/MS and focuses on the practical application of the technique in these two interrelated areas.

Postpartum maternal iodine status and the relationship to neonatal thyroid function.

Iodine deficiency in the postpartum period has the potential to affect neonatal neuropsychointellectual development. We performed a cross-sectional study involving 50 postpartum women and their neonates, measuring maternal urine iodine, breast milk iodine, and neonatal thyroid stimulating hormone (TSH), and examining their interrelationships. Women were studied at a median (range) of 4 (3-9) days postpartum. Moderate to severe iodine deficiency (defined by urine iodine concentration < 50 microg/L) was found in 29 of the 50 subjects (58%). The median +/- standard deviation (SD) urine iodine was 46.8 +/- 28.5 microg/L and the mean urine iodine expressed in micrograms per gram of creatinine was 86.6 +/- 45.6. The median (range) breast milk iodine was 84.0 microg/L (25.0-234.0). Breast milk iodine was significantly correlated with urine iodine in micrograms per gram of creatinine (r = 0.52, p < 0.001) but not with urine iodine measured in micrograms per liter (r = 0.19, p = 0.2). Six percent of neonates had whole-blood TSH values of greater than 5 mIU/L. Neonatal TSH levels were positively correlated with higher breast milk iodine (r = 0.42, p = 0.003). There was no significant correlation between neonatal TSH levels and the mothers urine iodine content. There is a high prevalence of iodine deficiency in these lactating postpartum subjects. Urine iodine as micrograms per gram of creatinine is a good predictor of breast milk iodine content. In our study, higher breast milk iodine was correlated with a higher neonatal TSH. The impact of breast milk iodine content on neonatal TSH levels and neuropsychointellectual development needs further study.

Newborn screening methods for cystic fibrosis.

An efficient newborn screening test for detecting cystic fibrosis has been available for over 20 years but is only now coming into widespread use. Blood immunoreactive trypsin is elevated in babies with cystic fibrosis and its measurement in dried blood spots is the primary screening tool. Poor discrimination in the first week requires a re-sampling step. The identification of the cystic fibrosis transmembrane conductance regulator gene and the discovery of a common mutation has allowed a combination of the primary screening test with a DNA test using the same sample. Differing genetic backgrounds have led to the development of population-specific protocols. A false-negative rate of around 5% is usual. Specificity is high. In all protocols involving a DNA test, confirmation of the diagnosis by sweat test is necessary when only one mutation is identified, identification of some carriers therefore being unavoidable. Careful counselling is needed for the families of these carriers.

Newborn screening may fail to identify intermediate forms of maple syrup urine disease

SummaryThe New South Wales state-wide newborn screening programme has offered comprehensive screening for inborn errors of metabolism, including MSUD, using electrospray tandem mass spectrometry since 1998. Over this period, a number of patients with classic MSUD have been identified with subsequent good neurological outcome. We describe two patients with an intermediate form of MSUD who presented later in childhood. Retrospective review of their newborn screening results demonstrates that the diagnosis could not have been made by current newborn screening. Their neurological outcome is much less satisfactory. Despite the usefulness of expanded newborn screening programmes in detecting severe neonatal presentations of inborn errors of metabolism, partial enzyme deficiencies may not be detected. Metabolic diseases still need to be considered in appropriate clinical situations later in life.

Carnitine palmitoyltransferase I deficiency in neonate identified by dried blood spot free carnitine and acylcarnitine profile

A neonate at risk for hepatic carnitine palmitoyltransferase I (L-CPT I) deficiency was investigated from birth. The free carnitine and acylcarnitine profile in dried whole blood filter paper samples collected at ages 1 and 4 days showed a markedly elevated concentration of free carnitine (141 and 142 μmol/L, respectively), normal concentrations of acetyl- and propionylcarnitine, with the near absence of all other species. The diagnosis was confirmed by in vitro fatty acid oxidation screening assays and enzyme assay in cultured skin fibroblasts. Retrospective study of the newborn whole blood sample of the index case showed a similar profile (free carnitine 181 μmol/L). The newborn population distribution of free carnitine (n=143981) showed that only three samples had free carnitine >140 μmol/L (>99.9th centile), two were from L-CPT I-deficient neonates and one from a baby with sepsis. While there are other conditions that can cause elevated concentrations of free carnitine, an isolated elevation of free carnitine only in an apparently healthy term neonate warrants further investigation to exclude L-CPT I deficiency.

Maternal attitudes to newborn screening for fragile X syndrome.

Although fragile X syndrome (FXS) is the commonest cause of inherited intellectual disability the mean age of diagnosis in Australia is 5.5 years. Newborn screening for FXS can provide an early diagnosis, preventing the “diagnostic odyssey”, allowing access to early interventions, and providing reproductive information for parents. Parents of affected children support newborn screening, but few clinical studies have evaluated community attitudes. A pilot study in 2009–2010 was performed in a tertiary hospital to explore feasibility and maternal attitudes. FXS testing of male and female newborns was offered to mothers in addition to routine newborn screening. Mothers were provided with information about FXS, inheritance pattern, carrier status, and associated adult‐onset disorders. One thousand nine hundred seventy‐one of 2,094 mothers (94%) consented to testing of 2,000 newborns. 86% completed the attitudinal survey and 10% provided written comments. Almost all parents (99%) elected to be informed of both premutation and full mutation status and there was little concern about identification of carrier status or associated adult‐onset disorders. Most mothers (96%) were comfortable being approached in the postnatal period and supported testing because no extra blood test was required. Mothers considered an early diagnosis beneficial to help prepare for a child with additional needs (93%) and for reproductive planning (64%). Some were anxious about the potential test results (10%) and others felt their feelings towards their newborn may change if diagnosed with FXS (16%). High participation rates and maternal attitudes indicate a high level of maternal acceptance and voluntary support for newborn screening for FXS.

Two-year pilot study of newborn screening for congenital adrenal hyperlasia in New South Wales compared with nationwide case surveillance in Australia

Aim:  To assess the benefits and practicalities of setting up a newborn screening (NBS) program in Australia for congenital adrenal hyperplasia (CAH) through a 2 year pilot screening in ACT/NSW and comparing with case surveillance in other states.