Age-Specific Cut-off Values of Amino Acids and Acylcarnitines for Diagnosis of Inborn Errors of Metabolism Using Liquid Chromatography Tandem Mass Spectrometry

The effect of common blood sampling types on metabolic screening

Capillary blood is often used for dried blood spot samples in metabolic screening tests. This study's objective is to examine the amino acid and acylcarnitine levels in the commonly used sampling types from the same subjects and compare the findings with capillary whole blood samples as the reference. Thirty adult patipicants' blood samples were collected into four different tubes: citrated tubes, serum separating tubes, heparin tubes, and EDTA tubes, respectively and additionally into the syringe. 50 μL blood from each tube and syringe was absorbed onto filter papers. Additionally, capillary whole blood taken from each person's fingertip was absorbed onto the filter paper. All measurements were performed with flow-injection analysis tandem mass spectrometry. In the pairwise comparison of fingertip group and other groups, almost all results were different from the reference group (p < 0.05), except for glutamine and methionine for amino acid analysis. The difference in acylcarnitine levels is not as obvious as in amino acid levels. If other sampling types are used for metabolic screening instead of capillary whole blood, it may lead to low results, especially in amino acid measurements. Additionally, cut-off values should be interpreted, taking into consideration the sampling type, and laboratories should be informed about the sampling type used.

Tandem mass spectrometry in screening for inborn errors of metabolism: comprehensive bibliometric analysis

Tandem mass spectrometry (MS/MS) for detection of inborn errors of metabolism (IEM) is recognized as an ethical, safe, simple, and reliable screening test. Presented bibliometric analysis aims to describe the network structure of the scientific community in the study area at the level of countries, institutions, authors, papers, keywords, and sources; scientific productivity, directions, and collaboration efforts in a considered period (1991-2024, May). Using the PRISMA method, we conducted a systematic search for articles reporting using MS/MS to screen for inherited metabolic disorders and inborn errors of metabolism collected from the Web of Science Core Collection (WoSCC). A total of 677 articles out of 826, by 3,714 authors, published in 245 journals, with 21,193 citations in 11,295 citing articles, with an average citation of 31.3 per article, and an H-index of 69 were retrieved from the WoSCC. The research status of MS/MS in IEM screening was identified. The most relevant current research directions and future areas of interest were revealed: "selective screening for IEM," "new treatments for IEM," "new disorders considered for MS/MS testing," "ethical issues associated with newborn screening," "new technologies that may be used for newborn screening," and "use of a combination of MS/MS and gene sequencing".

Consolidated Newborn Bloodspot Screening Efforts in Developing Countries in the Asia Pacific-2024

Approximately half of all births globally occur in the Asia Pacific Region. Concerted efforts to support local activities aimed at developing national newborn screening (NBS) have been ongoing for almost 30 years, first by the International Atomic Energy Agency (IAEA) and then through volunteer efforts. Sustainable newborn bloodspot screening (NBS) continues to be initiated and develop in many of the countries with developing economies in the region. Since the discontinuation of IAEA funding in 2007, a working group of the Asia Pacific Society of Human Genetics (APSHG) consisting of interested representatives from countries in the region with less than 50% NBS coverage has participated in periodic workshops to exchange information, set goals, and provide peer support. Facilitated by international NBS experts, interested corporate sponsors, and the APSHG, the 7th workshop of representatives from 10 East Asian countries with developing NBS systems was recently held in Kathmandu, Nepal. This report summarizes the NBS activities in these countries and describes the continuing efforts to move NBS ahead in the region.

Performance Validation of the NeoBase 2 Non-Derivatized MSMS Assay Kit and Cutoff Values Establishment of Term and Preterm Neonates

OBJECTIVE

NeoBase 2 Non-derivatized MSMS assay kit (NeoBase 2 kit) was used for newborn screening, the performance of the NeoBase 2 kit should be validated before its implementation in clinical diagnostic laboratories.

METHODS

Leftover dried blood spot samples, quality control materials in the NeoBase 2 kit, and proficiency testing materials received from the NSQAP were used. Precision, accuracy, LOD, LLOQ, recovery, and stability were carried out to verify the performance of the Waters ACQUITY TQD MS/MS system with the NeoBase 2 kit for newborn screening. Cutoffs were determined and analytes requiring different cutoffs in preterm neonates were investigated.

RESULTS

Within-run and between-run precisions ranged from 3.95% to 14.41%. The accuracy and stability were within 15%. All analytes demonstrated acceptable LOD, LLOQ, and recoveries. Cutoffs for term and preterm neonates were established.

CONCLUSIONS

The performance of the NeoBase 2 kit is acceptable and can be implemented in clinical diagnostic laboratories.

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

Determining the Reference Range of Amino Acids in Healthy Neonatal Blood Samples in Northeast Iran Using LC-MS/MS

Background

Amino acid analysis is an important tool for the diagnosis of metabolic disorders in newborns. Today, Liquid Chromatography tandem mass spectrometry (LC-MS/MS) has emerged as a powerful technique for amino acid analysis. We aimed to determine the local normal range of amino acids in dried blood spot (DBS) samples of neonates using LC-MS/MS.

Methods

A total of 1005 samples from healthy neonates of northeast and east of Iran aged 2-7 days were utilized for normal range determination. The amino acids were extracted from dried blood spot samples using organic solvent and then analyzed using LC-MS/MS system. The 1%, 2.5%, 97.5%, and 99% percentiles were calculated, and the results were compared to the global cut-off values.

Results

The results showed that glutamic acid has the highest concentration range among amino acids evaluated in this study (178.94 - 421.31µmol/L). Moreover, the plasma concentrations of Glycine (142.65 - 397.06 µmol/L), Alanine (97.00-349.72 µmol/L), Proline (63.77 - 236.53 µmol/L), and Tyrosine (25.79 - 150.58 µmol/L) were in the next ranks. Comparing the obtained results with the global values obtained in the R4S study indicated a slight difference between the obtained local normal values and the global values.

Conclusions

The calculated values were slightly different from global values obtained in the R4S study and regional values calculated in other studies. This further emphasized the importance of the local establishment of reference values, which facilitates the correct interpretation and diagnosis in the Newborn Screening Programs.

Selective screening for inborn errors of metabolism using tandem mass spectrometry in West Kazakhstan children: study protocol

Data on the prevalence of most inborn errors of metabolism are still unavailable in Kazakhstan. The study aims to perform selective screening for hereditary metabolic diseases among patients aged from 1 day to 18 years in western Kazakhstan using the LC-MS/MS method, with establishing the reference values for the content of amino acids, acylcarnitines, and succinylacetone in blood samples of healthy children. Tasks: 1. To assess the burden of metabolic disorders detected by LC-MS/MS in western Kazakhstan by examination of children at clinical risk in pediatric clinics throughout the region; https://www.frontiersin.org/register?returnUrl=https://loop.frontiersin.org 2. To set the reference values of metabolites in the child population; 3. To analyze the age distribution, prevalence, and age of onset for each identified IEM, further comparing the obtained findings with those from previously published reports in other populations.

METHODS

To set the reference values of 51 metabolites in the child population, 750 healthy children will be included. The selective screening will be performed among 1,500 patients aged 1 day to 18 years with suspected hereditary metabolic disorders.

ANTICIPATED RESULTS

The results of selective screening will be interpreted by comparison with the reference values established. Diagnosis will be based on clinical signs, blood levels of amino acids, acylcarnitines, succinylacetone, and urine levels of organic acids and tests for gene mutations. An assessment of 37 inborn errors of metabolism frequencies in high-risk children will be performed. The research will further develop the national as selective as expanded newborn screening programs. The study was registered in clinicaltrials. gov (https://www.

CLINICALTRIALS

gov/study/NCT05910151) on 16 June 2023.

Establishment of age- and -gender specific reference intervals for amino acids and acylcarnitines by tandem mass spectrometry in Turkish paediatric population

Introduction

We determined age- and gender-specific reference intervals (RIs) for acylcarnitines and amino acids by tandem mass spectrometry (MS/MS) in the Turkish paediatric population by using laboratory information system (LIS) data.

Materials and methods

A total of 9156 MS/MS results of children between 0-18 years of age, were downloaded from the LIS. Premature infants and newborns followed in the intensive care unit were excluded and only the first result of each patient attending outpatient clinics was included. Children with a known or suspected diagnosis of metabolic disease, malignancy, epilepsy, mental retardation, or genetic disorder were excluded. Laboratory results were evaluated and children with any pathological laboratory finding were excluded, resulting in a final sample size of 3357 (2029 boys and 1328 girls). Blood was collected by capillary puncture and spotted on Whatman 903 filter paper cards and analysed by MS/MS (Shimadzu LCMS-8050, Shimadzu Corporation, Kyoto, Japan). Data were evaluated for age and gender differences and age partitioning was performed according to the literature and visual evaluation of the data. Age subgroups were: ≤ 1 month, 2 months-1 year, 2-5 years, 6-10 years, and 11-18 years.

Results

There were significant age-related differences for the majority of amino acids and acylcarnitines thus age dependent RIs were established. Gender-specific RIs were established for tyrosine, leucine-isoleucine, isovalerylcarnitine (C5) and hexadecanoylcarnitine (C16).

Conclusions

Establishing age-related RIs can enhance the quality of medical care by facilitating early diagnosis and therapy, especially in certain metabolic disorders presenting with mild biochemical abnormalities and subtle clinical manifestations.

Assessment of reference intervals of acylcarnitines in newborns in Siberia

   Background. The incidence of diseases associated with impaired transport and oxidation of fatty acids is from 1:5,000 to 1:9,000 newborns. High morbidity, risk of death in the absence of timely correction, non-specificity of clinical manifestations define the importance of their timely laboratory diagnosis based on the determination of free carnitine and acylcarnitines in the blood. Reference values for free carnitine and acylcarnitines vary in different populations.   The aim. To determine the reference intervals of free carnitine and acylcarnitines in newborns of the Irkutsk region and to compare them with similar reference intervals in newborns in other countries.   Methods. The analysis of 229 samples of drу blood spots of healthy newborn children of the Irkutsk region aged from 0 to 7 days was carried out. Analysis of acylcarnitine concentrations was performed using high performance liquid chromatography with tandem mass spectrometry.   Results. 2.5 and 97.5 percentiles (µmol/l) were calculateed for 13 acylcarnitines: C0 – [8.78; 38.08]; C2 – [3.55; 19.09]; C3 – [0.33; 1.96]; C4 – [0.08; 0.51]; C5 – [0.06; 0.44]; C5DC – [0.03; 0.17]; C6 – [0.01; 0.07]; C8 – [0.01; 0.07]; C10 – [0.02; 0.07]; C12 – [0.04; 0.51]; C14 – [0.07; 0.24]; C16 – [0.58; 3.25]; C18 – [0.35; 1.16].   Conclusion. Differences in acylcarnitine reference intervals were found: compared with other countries, the concentrations of reference intervals for C0, C2, C3, C5DC, C8, C10, C14, C16 and C18 were lower in our study, reference intervals for C5 and C12 were higher in our country.

Newborn screening for propionic, methylmalonic acidemia and vitamin B12 deficiency. Analysis of 588,793 newborns

OBJECTIVES

We present the results of our experience in the diagnosis and follow up of the positive cases for propionic, methylmalonic acidemias and cobalamin deficiencies (PA/MMA/MMAHC) since the Expanded Newborn Screening was implemented in Madrid Region.

METHODS

Dried blood samples were collected 48 h after birth. Amino acids and acylcarnitines were quantitated by MS/MS. Newborns with alterations were referred to the clinical centers for follow-up. Biochemical and molecular genetic studies for confirmation of a disease were performed.

RESULTS

In the period 2011-2020, 588,793 children were screened, being 953 of them were referred to clinical units for abnormal result (192 for elevated C3 levels). Among them, 88 were false positive cases, 85 maternal vitamin B12 deficiencies and 19 were confirmed to suffer an IEM (8 PA, 4 MMA, 7 MMAHC). Ten out 19 cases displayed symptoms before the NBS results (6 PA, 1 MMA, 3 MMAHC). C3, C16:1OH+C17 levels and C3/C2 and C3/Met ratios were higher in newborns with PA/MMA/MMAHC. Cases diagnosed with B12 deficiency had mean B12 levels of 187.6 ± 76.9 pg/mL and their mothers 213.7 ± 95.0; 5% of the mothers were vegetarian or had poor eating while 15% were diagnosed of pernicious anemia. Newborns and their mothers received treatment with B12 with different posology, normalizing their levels and the secondary alterations disappeared.

CONCLUSIONS

Elevated C3 are a frequent cause for abnormal result in newborn screening with a high rate of false positive cases. Presymptomatic diagnosis of most of PA and some MMA/MMAHC is difficult. Vitamin B12 deficiency secondary to maternal deprivation is frequent with an heterogenous clinical and biochemical spectrum.

Targeted metabolomic profiles of serum amino acids and acylcarnitines related to gastric cancer

Background

Early diagnosis and treatment are imperative for improving survival in gastric cancer (GC). This work aimed to assess the ability of human serum amino acid and acylcarnitine profiles in distinguishing GC cases from atrophic gastritis (AG) and control superficial gastritis (SG) patients.

Methods

Sixty-nine GC, seventy-four AG and seventy-two SG control patients treated from May 2018 to May 2019 in Gansu Provincial Hospitalwere included. The levels of 42 serum metabolites in the GC, AG and SG groups were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Then, orthogonal partial least squares discriminant analysis (OPLS-DA) and the Kruskal-Wallis H test were used to identify a metabolomic signature among the three groups. Metabolites with highest significance were examined for further validation. Receiver operating characteristic (ROC) curve analysis was carried out for evaluating diagnostic utility.

Results

The metabolomic analysis found adipylcarnitine (C6DC), 3-hydroxy-hexadecanoylcarnitine (C16OH), hexanoylcarnitine (C6), free carnitine (C0) and arginine (ARG) were differentially expressed (all VIP >1) and could distinguish GC patients from AG and SG cases. In comparison with the AG and SG groups, GC cases had significantly higher C6DC, C16OH, C6, C0 and ARG amounts. Jointly quantitating these five metabolites had specificity and sensitivity in GC diagnosis of 98.55% and 99.32%, respectively, with an area under the ROC curve (AUC) of 0.9977.

Conclusion

This study indicates C6DC, C16OH, C6, C0 and ARG could effectively differentiate GC cases from AG and SG patients, and may jointly serve as a valuable circulating multi-marker panel for GC detection.

Identification of the metabolic signatures of prostate cancer by mass spectrometry-based plasma and urine metabolomics analysis

OBJECTIVE

Prostate cancer (PCa) is one of the most commonly diagnosed cancers among men which is associated with profound metabolic changes. Systematic analysis of the metabolic alterations and identification of new biomarkers may benefit PCa diagnosis and a deep understanding of the pathological mechanism. The purpose of this study was to determine the metabolic features of PCa.

METHODS

Plasma and urine metabolites from 89 prostate cancer (PCa) patients, 84 benign prostatic hyperplasia (BPH) patients, and 70 healthy males were analyzed using LC-MS/MS and GC-MS. The Orthogonalised Partial Least Squares Discriminant Analysis (OPLS-DA) was used to find the significantly changed metabolites. The clinical value of the candidate markers was examined by receiver operating characteristic curve analysis and compared with prostate-specific antigen (PSA).

RESULTS

Multivariate statistical analyses found a series of altered metabolites, which related to the urea cycle, tricarboxylic acid cycle (TCA), fatty acid metabolism, and the glycine cleavage system. Plasma Glu/Gln showed the highest predictive value (AUC = 0.984) when differentiating PCa patients from healthy controls, with a higher sensitivity than PSA (96.6% vs. 94.4%). Both Glu/Gln and PSA displayed a low specificity when differentiating PCa patients from BPH patients (<53.2%), while the combination of Glu/Gln and PSA can further increase the diagnostic specificity to 66.9%.

CONCLUSIONS

The present study showed the metabolic features of PCa, provided strong evidence that the amide nitrogen and the energy metabolic pathways could be a valuable source of markers for PCa. Several candidate markers identified in this study were clinically valuable for further assessment.

Rapid Electrochemical Screening of Phenylketonuria Maker Depending on Dehydrogenase Attached to the Pt-Doped Reduced Graphene Oxide Nanocomposites

Phenylketonuria (PKU) is a common disease associated with amino acid metabolism, and usually occurs in newborns. It can cause serious neurological diseases and even death. However, owing to inadequate-effective treatment, it can only be slowed by a low-phenylalanine (Phe) diet. In addition, PKU screening is essential for newborns in many countries. Therefore, rapid screening is crucial for preventing damage and meeting the large sample diagnosis demand. For confirmed patients, a convenient method to monitor their regular Phe levels is required. However, current clinical methods do not meet the rapid screening and convenient monitoring requirements. Herein, a rapid and facile electrochemical device based on platinum-doped reduced graphene oxide nanocomposites was developed to detect PKU biomarker-Phe. The results demonstrated that the developed electrode has great sensitivity, selectivity, and stability. The detection range was 0.0001 mM to 6 mM with a limit of detection of 0.01 μM. Therefore, this work offers a simple and rapid method for point-of-care PKU screening and daily monitoring.

The Application of Next-Generation Sequencing (NGS) in Neonatal-Onset Urea Cycle Disorders (UCDs): Clinical Course, Metabolomic Profiling, and Genetic Findings in Nine Chinese Hyperammonemia Patients

During Jan. 2016–Dec. 2019, nine Chinese patients from eight unrelated families were diagnosed with neonatal-onset UCDs by targeted panel sequencing or whole-exome sequencing (WES). Their clinical manifestations, biochemical features, 180-day-age outcomes, and molecular genetic characteristics were reviewed retrospectively. NGS-based tests revealed 7 patients diagnosed with ornithine transcarbamylase deficiency (OTCD) and 2 with carbamoylphosphate synthetase I deficiency (CPS1D). The spectrum of the clinical presentation of nine affected individuals progressed from unspecific symptoms like poor feeding to somnolence, coma, and death. All patients presented with an acute hyperammonemia. The most robust metabolic pattern in OTCD was hyperglutaminemic hyperammonemia with high concentration of urine orotic acid, and it was reported in six patients. Of ten variants found on the OTC gene and CPS1 gene, 3 were novel: (c.176T>C (p.L59P)) in the OTC gene, c.2938G>A (p.G980S) and c.3734T>A (p.L1245H) in the CPS1 gene. There was a high mortality rate of 77.78% (7/9) for all the defects combined. An OTC-deficient male and a CPS1-deficient female survived from episodes of hyperammonemia. Although prompt recognition of UCD and the use of alternative pathway therapy in addition to provision of appropriate nutrition and dialysis improved survival, the overall outcomes for the neonatal-onset type are poor in China.

Determination of methylmalonic acid, 2-methylcitric acid, and total homocysteine in dried blood spots by liquid chromatography-tandem mass spectrometry: A reliable follow-up method for propionylcarnitine-related disorders in newborn screening

OBJECTIVES

Determination of methylmalonic acid, 2-methylcitric acid, and total homocysteine in dried blood spots by liquid chromatography-tandem mass spectrometry has usually been used as a second-tier test to improve performance of newborn screening for propionylcarnitine-related disorders. However, factors that potentially affect its detection results have not been investigated, and we aimed to evaluate these influencing factors and explore their potential utility in newborn screening and initial follow-up for propionylcarnitine-related disorders.

METHODS

This study comprised a prospective group (1998 healthy infants, to establish cutoff values and investigate the influencing factors) and a retrospective group (804 suspected positive cases screened from 381, 399 newborns for propionylcarnitine-related disorders by tandem mass spectrometry, to evaluate the performance of newborn screening and initial follow-up).

RESULTS

Cutoff values for methylmalonic acid, 2-methylcitric acid, and total homocysteine were 2.12, 0.70, and 10.05 µmol/l, respectively. Concentration of methylmalonic acid, 2-methylcitric acid, and total homocysteine in dried blood spots is not impacted by sex, age, birth weight, gestational age, or dried blood spot storage time. A total of 75 of 804 cases were screened positive by combined tandem mass spectrometry and liquid chromatography-tandem mass spectrometry, thus eliminating 90% of the false positives without compromising sensitivity. Eighteen propionylcarnitine-related disorders were successfully identified, including one CblX case missed in the initial follow-up by tandem mass spectrometry.

CONCLUSIONS

Methylmalonic acid, 2-methylcitric acid, and total homocysteine detected in dried blood spots by liquid chromatography-tandem mass spectrometry is a reliable, specific, and sensitive approach for identifying propionylcarnitine-related disorders. We recommend this assay should be performed rather than tandem mass spectrometry in follow-up for propionylcarnitine-related disorders besides second-tier tests in newborn screening.

Quantitation of Urinary Acylcarnitines by DMS-MS/MS Uncovers the Effects of Total Body Irradiation in Cancer Patients

Acylcarnitines have been identified in human and animal metabolomic-profiling studies as urinary markers of radiation exposure, a result which is consistent with their cytoprotective effects and roles in energy metabolism. In the present work, a rapid method for quantitation of the more abundant acylcarnitines in human urine is developed using a valuable set of samples from cancer patients who received total body irradiation (TBI) at Memorial Sloan Kettering Cancer Center. The method uses solid-phase extraction (SPE) processing followed by differential mobility spectrometry (DMS with ethyl acetate modifier) tandem mass spectrometry (ESI-DMS-MS/MS) with deuterated internal standards. The analyzed human urine samples were collected from 38 individual patients at three time points over 24 h during and after the course of radiation treatment, a design allowing each patient to act as their own control and creatinine normalization. Creatinine-normalized concentrations for nine urinary acylcarnitine (acyl-CN) species are reported. Six acyl-CN species were reduced at the 6 h point. Acetylcarnitine (C2:0-CN) and valerylcarnitine (C5:0-CN) showed recovery at 24 h, but none of the other acyl-CN species showed recovery at that point. Levels of three acyl-CN species were not significantly altered by radiation. This rapid quantitative method for clinical samples covers the short- and medium-chain acylcarnitines and has the flexibility to be expanded to cover additional radiation-linked metabolites. The human data presented here indicates the utility of the current approach as a rapid, quantitative technique with potential applications by the medical community, by space research laboratories concerned with radiation exposure, and by disaster response groups.

Detection of Phenylketonuria Markers Using a ZIF-67 Encapsulated PtPd Alloy Nanoparticle (PtPd@ZIF-67)-Based Disposable Electrochemical Microsensor

Phenylketonuria (PKU) is a common disease in congenital disorder of amino acid metabolism, which can lead to intellectual disability, seizures, behavioral problems, and mental disorders. We report herein a facile method to screen for PKU by the measurements of its metabolites (markers). In this work, a disposable electrochemical microsensor modified with a ZIF (zeolitic imidazolate framework)-based nanocomposite is constructed, in which ZIF-67 crystals are encapsulated with PtPd alloy nanoparticles (NPs) forming the nanocomposite (PtPd@ZIF-67). According to electrochemical measurements, the PtPd@ZIF-67-modified microsensor shows good responses and selectivity to phenylpyruvic acid and phenylacetic acid, while almost no response toward other amino acid analogues is observed. Here, a new sensing mechanism based on the acylation reaction between the imidazole linker in ZIF-67 and carboxyl in PKU markers has been proposed and verified through the Fourier-transform infrared spectroscopy study. Moreover, the encapsulated PtPd NPs elevate the electron transfer capability of the PtPd@ZIF-67-modified microsensor and further improve the electrochemical sensing performance. Finally, we demonstrate that the developed PtPd@ZIF-67-modified microsensor has the possibility to sensing of PKU markers with high response and good specificity and may be extended to exploit the point-of-care rapid PKU screening.