Screening and diagnosis of beta-ureidopropionase deficiency by gas chromatographic/mass spectrometric analysis of urine

The relationship between beta-ureidopropionase deficiency due to UPB1 variants and human phenotypes is uncertain

BACKGROUND

Beta-ureidopropionase deficiency, caused by variants in UPB1, has been reported in association with various neurodevelopmental phenotypes including intellectual disability, seizures and autism.

AIM

We aimed to reassess the relationship between variants in UPB1 and a clinical phenotype.

METHODS

Literature review, calculation of carrier frequencies from population databases, long-term follow-up of a previously published case and reporting of additional cases.

RESULTS

Fifty-three published cases were identified, and two additional cases are reported here. Of these, 14 were asymptomatic and four had transient neurological features; clinical features in the remainder were variable and included non-neurological presentations. Several of the variants previously reported as pathogenic are present in population databases at frequencies higher than expected for a rare condition. In particular, the variant most frequently reported as pathogenic, p.Arg326Gln, is very common among East Asians, with a carrier frequency of 1 in 19 and 1 in 907 being homozygous for the variant in gnomAD v2.1.1.

CONCLUSION

Pending the availability of further evidence, UPB1 should be considered a 'gene of uncertain clinical significance'. Caution should be used in ascribing clinical significance to biochemical features of beta-ureidopropionase deficiency and/or UPB1 variants in patients with neurodevelopmental phenotypes. UPB1 is not currently suitable for inclusion in gene panels for reproductive genetic carrier screening.

SYNOPSIS

The relationship between beta-ureidopropionase deficiency due to UPB1 variants and clinical phenotypes is uncertain.

Case Report: A Case of β-Ureidopropionase Deficiency Complicated With MELAS Syndrome Caused by UPB1 Variant and Mitochondrial Gene Variant

BACKGROUND

β-Ureidopropionase deficiency is a rare autosomal recessive disease affecting the last step of pyrimidine degradation. Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a rare inherited disorder caused by genetic defects in mitochondrial DNA.

CASE PRESENTATION

One 8-year-old boy presented with dizziness, vomiting, and convulsions. The gas chromatography-mass spectrometry results suggested β-ureidopropionase deficiency. The whole-exome sequencing results revealed homozygous missense variant c.977G>A (p.R326Q) in UPB1. However, the patient presented with persistent hyperlactacidemia and metabolic acidosis, which did not correspond to the classic features of β-ureidopropionase deficiency. Combined with the manifestations of developmental delay, poor academic performance, and poor sports stamina, whole-mitochondrial-genome sequencing was performed. The results exhibited the variant m.3243A>G of MT-TL1 gene. The level of heterogeneity was 65% in the patient and 17.8% in his mother. Eventually, the final diagnosis of β-ureidopropionase deficiency combined with MELAS syndrome was made.

CONCLUSION

The report about β-ureidopropionase deficiency caused by a nuclear gene variant and MELAS syndrome caused by a mitochondrial gene variant coexisting in the same patient enriches the clinical study of these two rare diseases.

Clinical and genetic analysis of 7 Chinese patients with β-ureidopropionase deficiency

β-Ureidopropionase (βUP) deficiency is an autosomal recessive disease caused by abnormal changes in the pyrimidine-degradation pathway. This study aimed to investigate the mutation of β-ureidopropionase gene (UPB1) gene and clinical features of 7 Chinese patients with βUP deficiency.We reported 7 Chinese patients with βUP deficiency who were admitted at Tianjin Children's Hospital. Urine metabolomics was detected by gas chromatography-mass spectrometry (GC-MS). Then genetic testing of UPB1 was conducted by polymerase chain reaction (PCR) method.The patients presented with developmental delay, seizures, autism, abnormal magnetic resonance imaging, and significantly elevated levels of N-carbamyl-β-alanine and N-carbamyl-β-aminoisobutyric acid in urine. Subsequent analysis of UPB1 mutation revealed 2 novel missense mutations (c.851G>T and c.853G>A), 3 previously reported mutations including 2 missense mutations (c.977G>A and c.91G>A) and 1 splice site mutation (c.917-1 G>A).The results suggested that the UPB1 mutation may contribute to βUP deficiency. The c.977G>A is the most common mutation in Chinese population.

A Japanese case of β-ureidopropionase deficiency with dysmorphic features

β-Ureidopropionase deficiency is a rare autosomal recessive disease affecting the last step of pyrimidine degradation, and it is caused by a mutation in the UPB1 gene. Approximately 30 cases have been reported to date, with a phenotypical variability ranging from asymptomatic to severe neurological illness. Non-neurological symptoms have been rarely reported. We describe a case of this disease with developmental delay and dysmorphic features. Gas chromatography-mass spectrometry-based urine metabolomics demonstrated significant (⩾+4.5 standard deviation after logarithmic transformation) elevations of β-ureidopropionic acid and β-ureidoisobutyric acid, strongly suggesting a diagnosis of β-ureidopropionase deficiency. Subsequent quantitative analysis of pyrimidines by liquid chromatography-tandem mass spectrometry supported this finding. Genetic testing of the UPB1 gene confirmed compound heterozygosity of a novel mutation (c.976C>T) and a previously-reported mutation (c.977G>A) that is common in East Asians. β-Ureidopropionase deficiency is probably underdiagnosed, considering a wide phenotypical variability, non-specific neurological presentations, and an estimated prevalence of 1/5000-6000. Urine metabolomics should be considered for patients with unexplained neurological symptoms.

Genetic analysis of the UPB1 gene in two new Chinese families with β-ureidopropionase deficiency and the carrier frequency of the mutation c.977G>A in Northern China

PURPOSE

The purpose of the study was to investigate mutations of the UPB1 gene in two Chinese families with β-ureidopropionase deficiency and the heterozygous carrier frequency in Chinese.

METHODS

Genomic DNA was extracted from peripheral blood leukocytes from all available family members and 500 unrelated healthy controls. Then, all exons and flanking intron regions of the UPB1 gene were amplified by PCR and analyzed by direct sequencing in two patient-families. Finally, the carrier frequency of the c.977G>A (p.R326Q) mutation was identified by PCR restriction fragment length polymorphism in 500 healthy controls.

RESULTS

The two patients had the same homozygous missense mutation in exon 9 (c.977G>A; p.R326Q), and the carrier frequency of this mutation was 2.8 % in the Northern Chinese population, which suggests that about 1:5,102 Chinese are expected to suffer from UPB1 deficiency.

CONCLUSIONS

The c.977G>A (p.R326Q) is the most common mutation of the UPB1 gene in Chinese. The predicted incidence indicates that β-ureidopropionase deficiency is significantly underdiagnosed in the Chinese population. It should be necessary to add β-ureidopropionase deficiency to high-risk screening for the symptomatic patients group.

Clinical, biochemical and molecular analysis of 13 Japanese patients with β-ureidopropionase deficiency demonstrates high prevalence of the c.977G > A (p.R326Q) mutation [corrected]

β-ureidopropionase (βUP) deficiency is an autosomal recessive disease characterized by N-carbamyl-β-amino aciduria. To date, only 16 genetically confirmed patients with βUP deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 13 Japanese βUP deficient patients. In this group of patients, three novel missense mutations (p.G31S, p.E271K, and p.I286T) and a recently described mutation (p.R326Q) were identified. The p.R326Q mutation was detected in all 13 patients with eight patients being homozygous for this mutation. Screening for the p.R326Q mutation in 110 Japanese individuals showed an allele frequency of 0.9 %. Transient expression of mutant βUP enzymes in HEK293 cells showed that the p.E271K and p.R326Q mutations cause profound decreases in activity (≤ 1.3 %). Conversely, βUP enzymes containing the p.G31S and p.I286T mutations possess residual activities of 50 and 70 %, respectively, suggesting we cannot exclude the presence of additional mutations in the non-coding region of the UPB1 gene. Analysis of a human βUP homology model revealed that the effects of the mutations (p.G31S, p.E271K, and p.R326Q) on enzyme activity are most likely linked to improper oligomer assembly. Highly variable phenotypes ranging from neurological involvement (including convulsions and autism) to asymptomatic, were observed in diagnosed patients. High prevalence of p.R326Q in the normal Japanese population indicates that βUP deficiency is not as rare as generally considered and screening for βUP deficiency should be included in diagnosis of patients with unexplained neurological abnormalities.

ß-ureidopropionase deficiency: phenotype, genotype and protein structural consequences in 16 patients

ß-ureidopropionase is the third enzyme of the pyrimidine degradation pathway and catalyzes the conversion of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid to ß-alanine and ß-aminoisobutyric acid, ammonia and CO(2). To date, only five genetically confirmed patients with a complete ß-ureidopropionase deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 11 newly identified ß-ureidopropionase deficient patients as well as the analysis of the mutations in a three-dimensional framework. Patients presented mainly with neurological abnormalities (intellectual disabilities, seizures, abnormal tonus regulation, microcephaly, and malformations on neuro-imaging) and markedly elevated levels of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid in urine and plasma. Analysis of UPB1, encoding ß-ureidopropionase, showed 6 novel missense mutations and one novel splice-site mutation. Heterologous expression of the 6 mutant enzymes in Escherichia coli showed that all mutations yielded mutant ß-ureidopropionase proteins with significantly decreased activity. Analysis of a homology model of human ß-ureidopropionase generated using the crystal structure of the enzyme from Drosophila melanogaster indicated that the point mutations p.G235R, p.R236W and p.S264R lead to amino acid exchanges in the active site and therefore affect substrate binding and catalysis. The mutations L13S, R326Q and T359M resulted most likely in folding defects and oligomer assembly impairment. Two mutations were identified in several unrelated ß-ureidopropionase patients, indicating that ß-ureidopropionase deficiency may be more common than anticipated.

Five cases of beta-ureidopropionase deficiency detected by GC/MS analysis of urine metabolome

The clinical presentation of inborn errors of pyrimidine degradation varies considerably from asymptomatic to severe neurological illness. We have reported a method to screen for and make a chemical diagnosis of beta-ureidopropionase deficiency, leading to the discovery of the first asymptomatic case of this disease. In this method, the recovery of beta-ureidopropionate and beta-ureidoisobutyrate, the key biomarkers, was very high,and the adoption of GC/MS and targeted analysis enabled us to simultaneously obtain information related and unrelated to pyrimidine metabolism. The present study reports the results of a large-scale screening of 24,000 newborns using dried urine on filter paper. Identification of a total of four asymptomatic patients among newborns suggests the high incidence (1/6000) of this disease in Japan. While these newborns were asymptomatic, two additional cases detected at the age of 5 years as well as 3 months with this method for high-risk screening had autism and West syndrome, respectively.The key biomarkers and alpha-ureidobutyrate used as an internal standard were found to give not only their di-trimethylsilyl derivatives but also tri-trimethylsilyl derivatives, upon derivatization. The mass spectra and retention times of their tri-trimethylsilyl derivatives and data handling for quantification of the markers are presented.Identification of individuals with defects in pyrimidine metabolism would realize personalized medication in cancer chemotherapy with pyrimidine analogs such as 5-fluorouracil.

Genetic regulation of beta-ureidopropionase and its possible implication in altered uracil catabolism

OBJECTIVE

Approximately 30-40% of grade III-IV toxicity to 5-FU has been associated with partial or profound deficiency in dihydropyrimidine dehydrogenase (DPD), the first of three enzymes in the catabolic pathway of fluoropyrimidines. There remains, however, a subset of patients presenting with 5-FU-associated toxicity despite normal DPD activity, suggesting possible deficiencies in enzymes downstream of DPD: dihydropyrimidinase (DHP), encoded by the DPYS gene, and/or beta-ureidopropionase (BUP-1), encoded by the UPB1 gene. Previously, we reported the identification of inactivating mutations in the DPYS gene that could potentially alter the uracil catabolic pathway in healthy individuals with normal DPD enzyme activity. This study investigates the possible role of UPB1 genetic variations in the regulation of the uracil catabolic pathway in individuals presenting with a deficient uracil breath test (13C-UraBT) despite normal DPD enzyme activity.

METHODS

This study included 219 healthy asymptomatic volunteers with known DPD enzyme activity and [2-(13)C]-uracil breath test (UraBT). All samples were genotyped for sequence variations in the UPB1 gene using denaturing high performance liquid chromatography (DHPLC) and Surveyor enzyme digestion with confirmation of detected sequence variants by direct sequencing.

RESULTS

Seven novel and six previously reported sequence variations were identified, including one nonconservative mutation, which demonstrated 97.3% reduction in BUP-1 activity when expressed in the RKO cell line.

CONCLUSION

Data presented in this study demonstrate that alterations of uracil catabolism are not limited to DPD and/or DHP deficiency and that inactivating mutations in the UPB1 gene might impair uracil catabolism.

Beta-ureidopropionase deficiency presenting with congenital anomalies of the urogenital and colorectal systems

Beta-ureidopropionase deficiency (McKusick 606673) is an autosomal recessive condition caused by mutations in the UPB1 gene. To date, five patients have been reported, including one putative case detected through newborn screening. Clinical presentation includes neurological and developmental problems. Here, we report another case of beta-ureidopropionase deficiency who presented with congenital anomalies of the urogenital and colorectal systems and with normal neurodevelopmental milestones. Analysis of a urine sample, because of the suspicion of renal stones on ultrasound, showed strongly elevated levels of the characteristic metabolites, N-carbamyl-beta-amino acids. Subsequent analysis of UPB1 identified a novel mutation 209 G>C (R70P) in exon 2 and a previously reported splice receptor mutation IVS1-2A>G. Expression studies of the R70P mutant enzyme showed that the mutant enzyme did not possess any residual activity. Long-term follow-up is required to determine the clinical significance of the beta-ureidopropionase deficiency in our patient.

Noninvasive human metabolome analysis for differential diagnosis of inborn errors of metabolism

Early diagnosis and treatment are critical for patients with inborn errors of metabolism (IEMs). For most IEMs, the clinical presentations are variable and nonspecific, and routine laboratory tests do not indicate the etiology of the disease. A diagnostic procedure using highly sensitive gas chromatography-mass spectrometric urine metabolome analysis is useful for screening and chemical diagnosis of IEM. Metabolite analysis can comprehensively detect enzyme dysfunction caused by a variety of abnormalities. The mutations may be uncommon or unknown. The lack of coenzymes or activators and the presence of post-translational modification defects and subcellular localization abnormalities are also reflected in the metabolome. This noninvasive and feasible urine metabolome analysis, which uses urease-pretreatment, partial adoption of stable isotope dilution, and GC/MS, can be used to detect more than 130 metabolic disorders. It can also detect an acquired abnormal metabolic profile. The metabolic profiles for two cases of non-inherited phenylketonuria are shown. In this review, chemical diagnoses of hyperphenylalaninemia, phenylketonuria, hyperprolinemia, and lactic acidemia, and the differential diagnosis of beta-ureidopropionase deficiency and primary hyperammonemias including ornithine transcarbamylase deficiency and carbamoylphosphate synthetase deficiency are described.

Liquid chromatography–tandem mass spectrometric assay for the analysis of uracil, 5,6-dihydrouracil and β-ureidopropionic acid in urine for the measurement of the activities of the pyrimidine catabolic enzymes

A liquid chromatography-tandem mass spectrometric assay for the determination of uracil, 5,6-dihydrouracil and beta-ureidopropionic acid in urine was developed to measure the activities of enzymes involved in pyrimidine breakdown. The assay was required to investigate the relation between the uracil-dihydrouracil ratio and toxicities observed after treatment with fluoropyrimidines drugs. After addition of stable isotopically labelled internal standards, the analytes were isolated from a 100-microl urine sample using liquid-liquid extraction with ethyl acetate-2-propanol. Compounds were separated on an Atlantis dC18 column, using ammonium acetate-formic acid in water as the eluent. The eluate was totally led into an electrospray interface with positive ionisation and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the range 1.6-1600 microM, using both, artificial urine and pooled urine as matrices. Intra-day precisions were < or = 8% and inter-day precisions were < or = 10%. Accuracies between 91 and 108% were found. The analytes were chemically stable under all relevant conditions and the assay was successfully applied in two clinical studies of cancer patients treated with 5-fluorouracil or capecitabine.

beta-Ureidopropionase Deficiency Presenting with Febrile Status Epilepticus

Beta-ureidopropionase is the third enzyme in the catabolic pathway of uracil and thymine. To date, only three other patients are reported with this inborn error of metabolism. We report the clinical presentation of a male patient who presented at the age of 4 months after an ALTE-like event (ALTE = acute life-threatening event) with febrile status epilepticus. Such a clinical presentation has not been reported before in this condition. Diagnosis was based on biochemical, enzymatic and molecular studies. MRI (magnetic resonance imaging) at the age of 11 months demonstrated large subdural hematomata and global supratentorial atrophy. At that time the patient showed severe psychomotor retardation with muscular hypotonia, extremely limited visual contact and poorly controlled epilepsy.

CONCLUSIONS

Pyrimidine degradation defects should be included in the differential diagnosis of convulsions, (febrile) status epilepticus, psychomotor retardation and possibly also ALTE-like events.

Comprehensive analysis of pyrimidine metabolism in 450 children with unspecific neurological symptoms using high-pressure liquid chromatography-electrospray ionization tandem mass spectrometry

To evaluate the significance of inborn metabolic disorders of the pyrimidine degradation pathway, 450 children with unspecific neurological symptoms were comprehensively studied; 200 healthy children were recruited as controls. Uracil and thymine as well as their degradation products in urine were determined with an improved method based on reversed-phase HPLC coupled with electrospray ionization tandem mass spectrometry and detection by multiple-reaction monitoring using stable-isotope-labelled reference compounds as internal standards. From the results of the control group we established age-related reference ranges of all pyrimidine degradation products. In the patient group, two children with dihydropyrimidine dehydrogenase (DPYD) deficiency were identified; one of these was homozygous for the exon 14-skipping mutation of the DPYD gene. In addition, two patients with high uracil, dihydrouracil and beta-ureidopropionate were found to have ornithine transcarbamylase deficiency. In the urine of 9 patients, beta-alanine was markedly elevated owing to treatment with vigabatrin, an irreversible inhibitor of GABA transaminase, which interferes with beta-alanine breakdown. Four patients had exclusively high levels of beta-aminoisobutyrate (beta-AIB) due to a low activity of the D-beta-AIB-pyruvate aminotransferase, probably without clinical significance. In conclusion, quantitative investigation of pyrimidine metabolites in children with unexplained neurological symptoms, particularly epileptic seizures with or without psychomotor retardation, can be recommended as a helpful tool for diagnosis in clinical practice. Sensitive methods and age-related reference ranges enable the detection of partial enzyme deficiencies.

Rapid identification of dihydropyrimidine dehydrogenase deficiency by using a novel 2-13C-uracil breath test

PURPOSE

Dihydropyrimidine dehydrogenase (DPD)-deficient cancer patients have been shown to develop severe toxicity after administration of 5-fluorouracil. Routine determination of DPD activity is limited by time-consuming and labor-intensive methods. The purpose of this study was to develop a simple and rapid 2-(13)C-uracil breath test, which could be applied in most clinical settings to detect DPD-deficient cancer patients.

EXPERIMENTAL DESIGN

Fifty-eight individuals (50 "normal," 7 partially, and 1 profoundly DPD-deficient) ingested an aqueous solution of 2-(13)C-uracil (6 mg/kg). (13)CO(2) levels were determined in exhaled breath at various time intervals up to 180 min using IR spectroscopy (UBiT-IR(300)). DPD enzyme activity and DPYD genotype were determined by radioassay and denaturing high-performance liquid chromatography, respectively.

RESULTS

The mean (+/-SE) C(max), T(max), delta over baseline values at 50 min (DOB(50)) and cumulative percentage of (13)C dose recovered (PDR) for normal, partially, and profoundly DPD-deficient individuals were 186.4 +/- 3.9, 117.1 +/- 9.8, and 3.6 DOB; 52 +/- 2, 100 +/- 18.4, and 120 min; 174.1 +/- 4.6, 89.6 +/- 11.6, and 0.9 DOB(50); and 53.8 +/- 1.0, 36.9 +/- 2.4, and <1 PDR, respectively. The differences between the normal and DPD-deficient individuals were highly significant (all Ps <0.001).

CONCLUSIONS

We demonstrated statistically significant differences in the 2-(13)C-uracil breath test indices (C(max), T(max), DOB(50), and PDR) among healthy and DPD-deficient individuals. These data suggest that a single time-point determination (50 min) could rapidly identify DPD-deficient individuals with a less costly and time-consuming method that is applicable for most hospitals or physicians' offices.

β-Ureidopropionase deficiency: an inborn error of pyrimidine degradation associated with neurological abnormalities

beta-Ureidopropionase deficiency is an inborn error of the pyrimidine degradation pathway, affecting the cleavage of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid. In this study, we report the elucidation of the genetic basis underlying a beta-ureidopropionase deficiency in four patients presenting with neurological abnormalities and strongly elevated levels of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid in plasma, cerebrospinal fluid and urine. No beta-ureidopropionase activity could be detected in a liver biopsy obtained from one of the patients, which reflected the complete absence of the beta-ureidopropionase protein. Analysis of the beta-ureidopropionase gene (UPB1) of these patients revealed the presence of two splice-site mutations (IVS1-2A>G and IVS8-1G>A) and one missense mutation (A85E). Heterologous expression of the mutant enzyme in Escherichia coli showed that the A85E mutation resulted in a mutant beta-ureidopropionase enzyme without residual activity. Our results demonstrate that the N-carbamyl-beta-amino aciduria in these patients is due to a deficiency of beta-ureidopropionase, which is caused by mutations in the UPB1 gene. Furthermore, an altered homeostasis of beta-aminoisobutyric acid and/or increased oxidative stress might contribute to some of the clinical abnormalities encountered in patients with a beta-ureidopropionase deficiency. An analysis of the presence of the two splice site mutations and the missense mutation in 95 controls identified one individual who proved to be heterozygous for the IVS8-1G>A mutation. Thus, a beta-ureidopropionase deficiency might not be as rare as is generally considered.

Sensitive method for the quantification of urinary pyrimidine metabolites in healthy adults by gas chromatography-tandem mass spectrometry

Enzyme deficiencies in pyrimidine metabolism are associated with a risk for severe toxicity against the antineoplastic agent 5-fluorouracil. To assess whether urinary levels of pyrimidines and their metabolites can be used for predicting patients' individual phenotype, a new gas chromatographic-tandem mass spectrometric method was developed which allows the simultaneous determination of uracil and thymine and their metabolites dihydrouracil, dihydrothymine, beta-ureidopropionic acid, beta-ureidoisobutyric acid, and the amino acids beta-alanine and beta-aminoisobutyric acid in human urine. Small aliquots (2-20 microl) of the urine samples were evaporated and derivatized to the tert.-butyldimethylsilyl derivatives before quantification, using the respective stable isotope-labelled analogues as internal standards. Analytical variation was acceptable with an intra-day imprecision (RSD) below 10%, for beta-ureidoisobutyric acid below 15%. The method was used for investigating the stability of urine samples and the influence of urine collection at different times.

Diagnosis and monitoring of inborn errors of metabolism using urease-pretreatment of urine, isotope dilution, and gas chromatography-mass spectrometry

To diagnose inborn errors of metabolism, it would be desirable to simultaneously analyze and quantify organic acids, purines, pyrimidines, amino acids, sugars, polyols, and other compounds using a single-step fractionation; unfortunately, no such method currently exists. The present article will be concerned primarily with a practical yet comprehensive diagnostic procedure of inborn errors of metabolism (IEM). This procedure involves the use of urine or eluates from urine on filter paper, stable isotope dilution, and gas chromatography-mass spectrometry (GC-MS). This procedure not only offers reliable and quantitative evidence for diagnosing, understanding and monitoring the diseases, but also provides evidence for the diagnosis of new kinds of IEM. In this review, the differential diagnosis for hyperammonemia are described; deficiencies of ornithine carbamoyl transferase, argininosuccinate synthase (citrullinemia), argininosuccinate lyase and arginase, lysinuric protein intolerance, hyperammonemia-hyperornithinemia-homocitrullinemia syndrome, and citrullinemia type II. The diagnosis of IEM of purine and pyrimidine such as deficiencies of hypoxanthine-guanine phosphoribosyl transferase, adenine phosphoribosyl transferase, dihydropyrimidine dehydrogenase, dihydropyrimidinase and beta-ureidopropionase are described. During the pilot study for newborn screening, we found neonates with diseases at a rate of 1 per 1,400 including propionic acidemia, methylmalonic acidemia, orotic aciduria, beta-ureidopropionase deficiency, lactic aciduria and neuroblastoma. A rapid and reliable prenatal diagnosis for propionic acidemia is also described.