Newborn screening for aromatic l-amino acid decarboxylase deficiency - Strategies, results, and implication for prevalence calculations

BACKGROUND

Aromatic l-amino acid decarboxylase deficiency (AADCD) is a rare, autosomal-recessive neurometabolic disorder caused by variants in dopa decarboxylase (DDC) gene, resulting in a severe combined deficiency of serotonin, dopamine, norepinephrine, and epinephrine. Birth prevalence of AADCD varies by population. In pilot studies, 3-O-methyldopa (3-OMD) was shown to be a reliable biomarker for AADCD in high-throughput newborn screening (NBS) allowing an early diagnosis and access to gene therapy. To evaluate the usefulness of this method for routine NBS, 3-OMD screening results from the largest three German NBS centers were analyzed.

METHODS

A prospective, multicenter (n = 3) NBS pilot study evaluated screening for AADCD by quantifying 3-OMD in dried blood spots (DBS) using tandem mass spectrometry (MS/MS).

RESULTS

In total, 766,660 neonates were screened from January 2021 until June 2023 with 766,647 with unremarkable AADCD NBS (766,443 by 1st-tier analysis and 204 by 2nd-tier analysis) and 13 with positive NBS result recalled for confirmatory diagnostics (recall-rate about 1:59,000). Molecular genetic analysis confirmed AADCD (c.79C > T p.[Arg27Cys] in Exon 2 und c.215 A > C p.[His72Pro] in Exon 3) in one infant. Another individual was highly suspected with AADCD but died before confirmation (overall positive predictive value 0.15). False-positive results were caused by maternal L-Dopa use (n = 2) and prematurity (30th and 36th week of gestation, n = 2). However, in 63% (n = 7) the underlying etiology for false positive results remained unexplained. Estimated birth prevalence (95% confidence interval) was 1:766,660 (95% CI 1:775,194; 1:769,231) to 1:383,330 (95% CI 1:384,615; 1:383,142). The identified child remained asymptomatic until last follow up at the age of 9 months.

CONCLUSIONS

The proposed screening strategy with 3-OMD detection in DBS is feasible and effective to identify individuals with AADCD. The estimated birth prevalence supports earlier estimations and confirms AADCD as a very rare disorder. Pre-symptomatic identification by NBS allows a disease severity adapted drug support to diminish clinical complications until individuals are old enough for the application of the gene therapy.

Carrier frequency and incidence of aromatic L-amino acid decarboxylase deficiency: a gnomAD-based study

BACKGROUND

Aromatic L-amino acid decarboxylase (AADC) deficiency is an autosomal recessive neurotransmitter metabolism disorder and is clinically characterized by infancy hypotonia, ophthalmic crisis, and developmental delay. With the emergence of gene therapy for AADC deficiency, accurate prediction of AADC deficiency is required. This study aimed to analyze the carrier frequency and expected incidence of AADC deficiency using exome data from the Genome Aggregation Database (gnomAD).

METHODS

We analyzed 125,748 exomes from gnomAD, including 9197 East Asian exomes, for the DDC gene. All identified variants were classified according to the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines.

RESULTS

The worldwide carrier frequency of AADC deficiency was 0.17%; the highest frequency was observed in East Asians at 0.78%, and the lowest was in Latinos at 0.07%. The estimated incidence of AADC deficiency was 1 in 1,374,129 worldwide and 1 in 65,266 in East Asians.

CONCLUSION

The results demonstrated that East Asians have a higher carrier frequency of AADC deficiency than other ethnic groups. The variant spectrum of DDC genes in East Asian populations differed greatly from those of other ethnic groups. Our data will serve as a reference for further investigation of AADC deficiency.

IMPACT

This study analyzed exome data from the Genome Aggregation Database (gnomAD) to estimate the carrier frequency and expected incidence of aromatic L-amino acid decarboxylase (AADC) deficiency. The article provides updated carrier frequency and incidence estimates for AADC deficiency, particularly in East Asian populations, and emphasizes the significant differences in the variant spectrum of DDC genes in this population compared to other ethnic groups. The study provides important information for accurate prediction and early diagnosis of AADC deficiency, particularly in high-risk populations, and may aid in the development of more effective targeted screening programs and gene therapies for this disorder.

Biochemical and molecular features of chinese patients with glutaric acidemia type 1 from Fujian Province, southeastern China

BACKGROUND

Glutaric acidemia type 1 (GA1) is a rare autosomal recessive inherited metabolic disorder caused by variants in the gene encoding the enzyme glutaryl-CoA dehydrogenase (GCDH). The estimated prevalence of GA1 and the mutational spectrum of the GCDH gene vary widely according to race and region. The aim of this study was to assess the acylcarnitine profiles and genetic characteristics of patients with GA1 in Fujian Province, southeastern China.

RESULTS

From January 2014 to December 2022, a total of 1,151,069 newborns (631,016 males and 520,053 females) were screened using MS/MS in six newborn screening (NBS) centers in Fujian Province and recruited for this study. Through NBS, 18 newborns (13 females and 5 males) were diagnosed with GA1. Thus, the estimated incidence of GA1 was 1 in 63,948 newborns in Fujian province. In addition, 17 patients with GA1 were recruited after clinical diagnosis. All but one patient with GA1 had a remarkable increase in glutarylcarnitine (C5DC) concentrations. The results of urinary organic acid analyses in 33 patients showed that the concentration of glutaric acid (GA) increased in all patients. The levels of C5DC and GA in patients identified via NBS were higher than those in patients identified via clinical diagnosis (P < 0.05). A total of 71 variants of 70 alleles were detected in patients with GA1, with 19 different pathogenic variants identified. The three most prevalent variants represented 73.23% of the total and were c.1244-2 A > C, p.(?) (63.38%), c.1261G > A, p.Ala421Thr (5.63%), and c.406G > T, p.Gly136Cys (4.22%). The most abundant genotype observed was c.[1244-2 A > C]; [1244-2 A > C] (18/35, 52.43%) and its phenotype corresponded to high excretors (HE, GA > 100 mmol/mol Cr).

CONCLUSIONS

In conclusion, we investigated the biochemical and molecular features of 35 unrelated patients with GA1. C5DC concentrations in dried blood spots and urinary GA are effective indicators for a GA1 diagnosis. Our study also identified a GCDH variant spectrum in patients with GA1 from Fujian Province, southeastern China. Correlation analysis between genotypes and phenotypes provides preliminary and valuable information for genetic counseling and management.

Prevalence of DDC genotypes in patients with aromatic L-amino acid decarboxylase (AADC) deficiency and in silico prediction of structural protein changes

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive genetic disorder affecting the biosynthesis of dopamine, a precursor of both norepinephrine and epinephrine, and serotonin. Diagnosis is based on the analysis of CSF or plasma metabolites, AADC activity in plasma and genetic testing for variants in the DDC gene. The exact prevalence of AADC deficiency, the number of patients, and the variant and genotype prevalence are not known. Here, we present the DDC variant (n = 143) and genotype (n = 151) prevalence of 348 patients with AADC deficiency, 121 of whom were previously not reported. In addition, we report 26 new DDC variants, classify them according to the ACMG/AMP/ACGS recommendations for pathogenicity and score them based on the predicted structural effect. The splice variant c.714+4A>T, with a founder effect in Taiwan and China, was the most common variant (allele frequency = 32.4%), and c.[714+4A>T];[714+4A>T] was the most common genotype (genotype frequency = 21.3%). Approximately 90% of genotypes had variants classified as pathogenic or likely pathogenic, while 7% had one VUS allele and 3% had two VUS alleles. Only one benign variant was reported. Homozygous and compound heterozygous genotypes were interpreted in terms of AADC protein and categorized as: i) devoid of full-length AADC, ii) bearing one type of AADC homodimeric variant or iii) producing an AADC protein population composed of two homodimeric and one heterodimeric variant. Based on structural features, a score was attributed for all homodimers, and a tentative prediction was advanced for the heterodimer. Almost all AADC protein variants were pathogenic or likely pathogenic.

Detection of 3-O-methyldopa in dried blood spots for neonatal diagnosis of aromatic L-amino-acid decarboxylase deficiency: The northeastern Italian experience

OBJECTIVE

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited autosomal recessive disorder of biogenic amine metabolism. Diagnosis requires analysis of neurotransmitter metabolites in cerebrospinal fluid, AADC enzyme activity analysis, or molecular analysis of the DDC gene. 3-O-methyldopa (3-OMD) is a key screening biomarker for AADC deficiency.

METHODS

We describe a rapid method for 3-OMD determination in dried blood spots (DBS) using flow-injection analysis tandem mass spectrometry with NeoBase™ 2 reagents and ¹³C₆-tyrosine as an internal standard, which are routinely used in high-throughput newborn screening. We assessed variability using quality control samples over a range of 3-OMD concentrations.

RESULTS

Within-day and between-day precision determined with quality control samples demonstrated coefficients of variation <15%. 3-OMD concentrations in 1000 healthy newborns revealed a mean of 1.33 μmol/L (SD ± 0.56, range 0.61-3.05 μmol/L), 100 non-AADC control subjects (age 7 days - 1 year) showed a mean of 1.19 μmol/L (SD ± 0.35-2.00 μmol/L), and 81 patients receiving oral L-Dopa had a mean 3-OMD concentration of 14.90 μmol/L (SD ± 14.18, range 0.4-80.3 μmol/L). A patient with confirmed AADC was retrospectively analyzed and correctly identified (3-OMD 10.51 μmol/L). In April 2020, we started a pilot project for identifying AADC deficiency in DBSs routinely submitted to the expanded newborn screening program. 3-OMD concentrations were measured in 21,867 samples; no patients with AADC deficiency were identified. One newborn had a high 3-OMD concentration due to maternal L-Dopa treatment.

DISCUSSION

We demonstrated a rapid new method to identify AADC deficiency using reagents and equipment already widely used in newborn screening programs. Although our study is limited, introduction of our method in expanded neonatal screening is feasible and could facilitate deployment of screening, allowing for early diagnosis that is important for effective treatment.

Spectrum analysis of inborn errors of metabolism for expanded newborn screening in a northwestern Chinese population

Expanded newborn screening facilitates early identification and intervention of patients with inborn errors of metabolism (IEMs), There is a lack of disease spectrum data for many areas in China. To determine the disease spectrum and genetic characteristics of IEMs in Xi'an city of Shaanxi province in northwest China, 146152 newborns were screening by MSMS from January 2014 to December 2019 and 61 patients were referred to genetic analysis by next generation sequencing (NGS) and validated by Sanger sequencing. Seventy-five newborns and two mothers were diagnosed with IEMs, with an overall incidence of 1:1898 (1:1949 without mothers). There were 35 newborns with amino acidemias (45.45%, 1:4176), 28 newborns with organic acidurias (36.36%, 1:5220), and 12 newborns and two mothers with FAO disorders (18.18%; 1:10439 or 1:12179 without mothers). Phenylketonuria and methylmalonic acidemia were the two most common disorders, accounting for 65.33% (49/75) of all confirmed newborn. Some hotspot mutations were observed for several IEMs, including PAH gene c.728G>A for phenylketonuria; MMACHC gene c.609G>A and c.567dupT, MMUT gene c.323G>A for methylmalonic acidemia and SLC25A13 gene c.852_855del for citrin deficiency. Our study provides effective clinical guidance for the popularization and application of expanded newborn screening, genetic screening, and genetic counseling of IEMs in this region.

[Newborn Screening Program in the Community of Madrid: evaluation of positive cases.]

OBJECTIVE

Tandem mass spectrometry (MS/MS) is being used for newborn screening since this laboratory testing technology increases the number of metabolic disorders that can be detected from dried blood-spot specimens. In the Community of Madrid, it was implemented in March 2011 and it includes 13 aminoacidopathies, fatty acid oxidation disorders and organic acidemias. The aim of this study was to describe our experience and evaluate the screening positive cases in a period of 9 years (2011-2019).

METHODS

During the period of the study, a total of 592.822 neonates were screened with this expanded program by MS/MS in the Community of Madrid. Amino acids, acylcarnitines, and succinylacetone were quantified in all samples that met the quality criteria. Means, medians, percentiles and standard deviation of the analytes and ratios of interest were calculated.

RESULTS

901 patients (0,15 %) with a positive screening test were referred to clinical evaluation. 230 patients were diagnosed of 30 different inborn errors of metabolism (prevalence 1:2577), 11 of which were not included as a target in the Community of Madrid newborn screening program. The global positive predictive value was 25,6 %. During this period of time, two false negative cases were detected. The most prevalent disorders were phenylketonuria/hyperphenylalaninemia and medium chain acyl-CoA dehydrogenase deficiency (1:6444 and 1:13174 respectively). 93 % of the patients were detected in the presymptomatic stage.

CONCLUSIONS

During the last 9 years a large number of cases of IEM have been detected with an acceptable global positive predictive value. These results confirm the utility of inborn errors of metabolism newborn screening as a public health program.

Glutaric acidemia type 1: Treatment and outcome of 168 patients over three decades

Glutaric acidemia type 1 (GA1) is a disorder of cerebral organic acid metabolism resulting from biallelic mutations of GCDH. Without treatment, GA1 causes striatal degeneration in >80% of affected children before two years of age. We analyzed clinical, biochemical, and developmental outcomes for 168 genotypically diverse GA1 patients managed at a single center over 31 years, here separated into three treatment cohorts: children in Cohort I (n = 60; DOB 2006-2019) were identified by newborn screening (NBS) and treated prospectively using a standardized protocol that included a lysine-free, arginine-enriched metabolic formula, enteral l-carnitine (100 mg/kg•day), and emergency intravenous (IV) infusions of dextrose, saline, and l-carnitine during illnesses; children in Cohort II (n = 57; DOB 1989-2018) were identified by NBS and treated with natural protein restriction (1.0-1.3 g/kg•day) and emergency IV infusions; children in Cohort III (n = 51; DOB 1973-2016) did not receive NBS or special diet. The incidence of striatal degeneration in Cohorts I, II, and III was 7%, 47%, and 90%, respectively (p < .0001). No neurologic injuries occurred after 19 months of age. Among uninjured children followed prospectively from birth (Cohort I), measures of growth, nutritional sufficiency, motor development, and cognitive function were normal. Adherence to metabolic formula and l-carnitine supplementation in Cohort I declined to 12% and 32%, respectively, by age 7 years. Cessation of strict dietary therapy altered plasma amino acid and carnitine concentrations but resulted in no serious adverse outcomes. In conclusion, neonatal diagnosis of GA1 coupled to management with lysine-free, arginine-enriched metabolic formula and emergency IV infusions during the first two years of life is safe and effective, preventing more than 90% of striatal injuries while supporting normal growth and psychomotor development. The need for dietary interventions and emergency IV therapies beyond early childhood is uncertain.

Incidence of newborn screening disorders among 56632 infants in Central Saudi Arabia. A 6-year study

Objectives:

To determine the incidence of newborn screening (NBS) disorders and to study the key performance indicators of the program.

Methods:

This retrospective single-center study enrolled all infants who underwent NBS from January 2012 to December 2017 at Prince Sultan Military Medical City, Riyadh, Saudi Arabia. We screened 17 NBS disorders. Blood samples were collected 24 hours after birth. If the initial result was positive, a second sample was collected. True positive cases were immediately referred for medical management. Data were extracted from laboratory computerized and non-computerized records using case report forms.

Results:

During the study period, 56632 infants underwent NBS with a coverage rate of 100%. Thirty-eight cases were confirmed. The incidence of congenital hypothyroidism was 1:3775. The positive predictive value for the detection of congenital hypothyroidism was 11.8%. Propionic aciduria was the most common metabolic disorder, with an incidence of 1:14158. Very long-chain acyl CoA dehydrogenase deficiency and glutaric aciduria type 1 had an incidence of 1:18877 each. Phenylketonuria, biotinidase deficiency, maple syrup urine disease, and citrullinemia had an incidence of 1:28316 each. However, galactosemia and 3-methyl crotonyl carboxylase deficiency had the lowest incidence of 1:56632.

Conclusion:

The NBS coverage rate at our facility was 100%. Congenital hypothyroidism was the most frequently detected disorder with an incidence that matches worldwide figures. The incidence of other inherited disorders was consistent with regional figures.

Molecular and biochemical study of glutaric aciduria type 1 in 49 Russian families: nine novel mutations in the GCDH gene

Glutaric aciduria type 1 (GA1, deficiency of glutaryl CoA dehydrogenase, glutaric acidemia type 1) (ICD-10 code: E72.3; MIM 231670) is an autosomal recessive disease caused by mutations in the gene encoding the enzyme glutaryl CoA dehydrogenase (GCDH). Herein, we present the biochemical and molecular genetic characteristics of 51 patients diagnosed with GA1 from 49 unrelated families in Russia. We identified a total of 21 variants, 9 of which were novel: c.127 + 1G > T, с.471_473delCGA, c.161 T > C (p.Leu54Pro), c.531C > A (р.Phe177Leu), c.647C > T (p.Ser216Leu), c.705G > A (р.Gly235Asp), c.898 G > A (р.Gly300Ser), c.1205G > C (р.Arg402Pro), c.1178G > A (р.Gly393Glu). The most commonly detected missense variants were c.1204C > T (p.Arg402Trp) and с.1262C > T (р.Ala421Val), which were identified in 56.38% and 11.7% of mutated alleles. A heterozygous microdeletion of the short arm (p) of chromosome 19 from position 12,994,984-13,003,217 (8233 b.p.) and from position 12,991,506-13,003,217 (11,711 b.p.) were detected in two patients. Genes located in the area of imbalance were KLF1, DNASE2, and GCDH. Patients presented typical GA1 biochemical changes in the biological fluids, except one patient with the homozygous mutation p.Val400Met. No correlation was found between the GCDH genotype and glutaric acid (GA) concentration in the cohort of our patients.

[Screening for carriers of pathogenic genes for methylmalonic acidemia and Wilson's disease in neonates in Qingdao]

Objective: To investigate the carrier frequency of pathogenic genes for methylmalonic acidemia and Wilson's disease in neonates in Qingdao. Methods: In this cross-sectional study, using computer random sampling, 5 020 neonates from the neonatal screening center in Qingdao area from June 2016 to December 2018 were selected, and 5 012 of them were included in the carrier screening study.DNA was extracted from dried blood stain specimens used in the screening of newborns. Multiplex PCR combined with next generation sequencing were used for gene detection of MMACHC gene, MUT gene and ATP7B gene. The carrying rate of hotspots of each gene were calculated, and binomial distribution method was used to calculate 95% confidence interval of pathogenic gene carrying rate. Results: A total of 5 012 neonates completed the screening for carriers of disease-causing genes, of which 5 006 neonates completed the screening of two diseases and the remaining 6 neonates completed the screening of Wilson disease only.For ATP7B gene, the carrier frequency of the 12 hot spot mutations was 1.46% (73/5 012),and the 95% confidence interval was 1.16%-1.83%. For MMACHC gene and MUT gene, carrier frequency of 18 hot spot mutations was 2.50% (125/5 006) , and the 95% confidence interval was 2.10%-2.97%, among which cblC type accounted for 87.2% and the MUT pathogenic gene accounted for 12.8%. Conclusion: The carrier frequency of methylmalonic acidemia and Wilson's disease are both high in the neonatal population in Qingdao.

Institutional experience of newborn screening for inborn metabolism disorders by tandem MS in the Turkish population

Background The tandem mass spectrometry method in the screening of congenital metabolic disorders is not included in routine national newborn screening programmes in Turkey. To evaluate the distribution of acylcarnitines and amino acid levels in normal newborns, establish acylcarnitine and amino acid cut-off levels and further preliminary results of inherited metabolic disorders inferentially in the Turkish population. Methods Newborn screening tests performed by tandem MS from 2016 to 2018 were retrospectively reviewed. The study group included 17,066 newborns born in our hospitals located in various regions of Turkey. Blood samples were obtained from infants older than 24 h of age. Among the 17,066 newborns, the metabolic screening data of 9,994 full-term newborns (>37 weeks) were employed to obtain the percentile distribution of the normal population. The study group (17,066) was screened for 26 types of inborn error of metabolism. Results Our established cut-offs, were compared with the cut-offs determined by Region for Stork Study and Centers for Disease Control. Among the 26 screened disorders, a total of 12 cases (8 amino acid metabolism disorders, 1 urea cycle defect, 2 organic acidaemias and 1 fatty acid oxidation disorder) were identified. Conclusions Because of the high rate of consanguineous marriages in Turkey, the development of a nationwide screening panel is necessary for early detection and management of potentially treatable inherited metabolic disorders.

Prevalence of Aromatic l-Amino Acid Decarboxylase Deficiency in At-Risk Populations

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency is an autosomal recessive metabolic disorder that results from disease-causing pathogenic variants of the dopa decarboxylase (DDC) gene. Loss of dopamine and serotonin production in the brain from infancy prevents achievement of motor developmental milestones.

METHODS

We retrospectively evaluated data obtained from requests to Medical Neurogenetics Laboratories for analyses of neurotransmitter metabolites in the cerebrospinal fluid, AADC enzyme activity in plasma, and/or Sanger sequencing of the DDC gene. Our primary objective was to estimate the prevalence of AADC deficiency in an at-risk population.

RESULTS

Approximately 20,000 cerebrospinal fluid samples were received with a request for neurotransmitter metabolite analysis in the eight-year study period; 22 samples tested positive for AADC deficiency based on decreased concentrations of 5-hydroxyindoleacetic acid and homovanillic acid, and increased 3-O-methyldopa, establishing an estimated prevalence of approximately 0.112%, or 1:900. Of the 81 requests received for plasma AADC enzyme analysis, 25 samples had very low plasma AADC activity consistent with AADC deficiency, resulting in identification of nine additional cases. A total of five additional patients were identified by Sanger sequencing as the primary request leading to the diagnosis of AADC deficiency.

CONCLUSIONS

Overall, these analyses identified 36 new cases of AADC deficiency. Sequencing findings showed substantial diversity with identification of 26 different DDC gene variants; five had not previously been associated with AADC deficiency. The results of the present study align with the emerging literature and understanding of the epidemiology and genetics of AADC deficiency.

Dietary practices in methylmalonic acidaemia: a European survey

Background The dietary management of methylmalonic acidaemia (MMA) is a low-protein diet providing sufficient energy to avoid catabolism and to limit production of methylmalonic acid. The goal is to achieve normal growth, good nutritional status and the maintenance of metabolic stability. Aim To describe the dietary management of patients with MMA across Europe. Methods A cross-sectional questionnaire was sent to European colleagues managing inherited metabolic disorders (IMDs) (n=53) with 27 questions about the nutritional management of organic acidaemias. Data were analysed by different age ranges (0-6 months; 7-12 months; 1-10 years; 11-16 years; >16 years). Results Questionnaires were returned from 53 centres. Twenty-five centres cared for 80 patients with MMA vitamin B12 responsive (MMAB12r) and 43 centres managed 215 patients with MMA vitamin B12 non-responsive (MMAB12nr). For MMAB12r patients, 44% of centres (n=11/25) prescribed natural protein below the World Health Organization/Food and Agriculture Organization/United Nations University (WHO/FAO/UNU) 2007 safe levels of protein intake in at least one age range. Precursor-free amino acids (PFAA) were prescribed by 40% of centres (10/25) caring for 36% (29/80) of all the patients. For MMAB12nr patients, 72% of centres (n=31/43) prescribed natural protein below the safe levels of protein intake (WHO/FAO/UNU 2007) in at least one age range. PFAA were prescribed by 77% of centres (n=33/43) managing 81% (n=174/215) of patients. In MMAB12nr patients, 90 (42%) required tube feeding: 25 via a nasogastric tube and 65 via a gastrostomy. Conclusions A high percentage of centres used PFAA in MMA patients together with a protein prescription that provided less than the safe levels of natural protein intake. However, there was inconsistent practices across Europe. Long-term efficacy studies are needed to study patient outcome when using PFAA with different severities of natural protein restrictions in patients with MMA to guide future practice.

Evaluation of dietary treatment and amino acid supplementation in organic acidurias and urea-cycle disorders: On the basis of information from a European multicenter registry

Organic acidurias (OAD) and urea-cycle disorders (UCD) are rare inherited disorders affecting amino acid and protein metabolism. As dietary practice varies widely, we assessed their long-term prescribed dietary treatment against published guideline and studied plasma amino acids levels. We analyzed data from the first visit recorded in the European registry and network for intoxication type metabolic diseases (E-IMD, Chafea no. 2010 12 01). In total, 271 methylmalonic aciduria (MMA) and propionic aciduria (PA) and 361 UCD patients were included. Median natural protein prescription was consistent with the recommended daily allowance (RDA), plasma L-valine (57%), and L-isoleucine (55%) levels in MMA and PA lay below reference ranges. Plasma levels were particularly low in patients who received amino acid mixtures (AAMs-OAD) and L-isoleucine:L-leucine:L-valine (BCAA) ratio was 1.0:3.0:3.2. In UCD patients, plasma L-valine, L-isoleucine, and L-leucine levels lay below reference ranges in 18%, 30%, and 31%, respectively. In symptomatic UCD patients who received AAM-UCD, the median natural protein prescription lay below RDA, while their L-valine and L-isoleucine levels and plasma BCAA ratios were comparable to those in patients who did not receive AAM-UCD. Notably, in patients with ornithine transcarbamylase syndrome (OTC-D), carbamylphosphate synthetase 1 syndrome (CPS1-D) and hyperammonemia-hyperornithinemia-homocitrullinemia (HHH) syndrome selective L-citrulline supplementation resulted in higher plasma L-arginine levels than selective L-arginine supplementation. In conclusion, while MMA and PA patients who received AAMs-OAD had very low BCAA levels and disturbed plasma BCAA ratios, AAMs-UCD seemed to help UCD patients obtain normal BCAA levels. In patients with OTC-D, CPS1-D, and HHH syndrome, selective L-citrulline seemed preferable to selective L-arginine supplementation.

Clinical Spectrum of Inherited Disorders of Metabolism

OBJECTIVE

To study the clinical profile and outcome of children with Inborn errors of metabolism.

METHODS

Thirty one newly diagnosed children with Inborn errors of metabolism over a 1 y period were studied for their relevant clinical, biochemical, diagnosis, treatment and follow-up details.

RESULTS

Inborn errors of metabolism accounted for 2% of hospital admissions. Sixty five percent were born to parents of consanguineous marriage. Of the 31 children with Inborn errors of metabolism, 16 (51%) had lysosomal storage disorders, 8 (26%) had disorders of amino acid metabolism, 2 (6%) each had disorders of carbohydrate and bile acid metabolism, 1 (3%) each had disorders of fatty acid oxidation, mitochondrial and peroxisome metabolism. Acrodermatitis dysmetabolica, as a complication was observed in one child and the overall mortality rate in this series was 10%.

CONCLUSIONS

Lysosomal storage disorders constituted the majority of Inborn errors of metabolism in this series and amino acidopathies/organic acidemias were successfully treated with special formulas.

Research, diagnosis and education in inborn errors of metabolism in Colombia: 20 years' experience from a reference center

The use of specialized centers has been the main alternative for an appropriate diagnosis, management and follow up of patients affected by inborn errors of metabolism (IEM). These centers facilitate the training of different professionals, as well as the research at basic, translational and clinical levels. Nevertheless, few reports have described the experience of these centers and their local and/or global impact in the study of IEM. In this paper, we describe the experience of a Colombian reference center for the research, diagnosis, training and education on IEM. During the last 20 years, important advances have been achieved in the clinical knowledge of these disorders, as well as in the local availability of several diagnosis tests. Organic acidurias have been the most frequently detected diseases, followed by aminoacidopathies and peroxisomal disorders. Research efforts have been focused in the production of recombinant proteins in microorganisms towards the development of new enzyme replacement therapies, the design of gene therapy vectors and the use of bioinformatics tools for the understanding of IEM. In addition, this center has participated in the education and training of a large number professionals at different levels, which has contributed to increase the knowledge and divulgation of these disorders along the country. Noteworthy, in close collaboration with patient advocacy groups, we have participated in the discussion and construction of initiatives for the inclusion of diagnosis tests and treatments in the health system.

Carnosinase, diabetes mellitus and the potential relevance of carnosinase deficiency

Carnosinase (CN1) is a dipeptidase, encoded by the CNDP1 gene, that degrades histidine-containing dipeptides, such as carnosine, anserine and homocarnosine. Loss of CN1 function (also called carnosinase deficiency or aminoacyl-histidine dipeptidase deficiency) has been reported in a small number of patients with highly elevated blood carnosine concentrations, denoted carnosinaemia; it is unclear whether the variety of clinical symptoms in these individuals is causally related to carnosinase deficiency. Reduced CN1 function should increase serum carnosine concentrations but the genetic basis of carnosinaemia has not been formally confirmed to be due to CNDP1 mutations. A CNDP1 polymorphism associated with low CN1 activity correlates with significantly reduced risk for diabetic nephropathy, especially in women with type 2 diabetes, and may slow progression of chronic kidney disease in children with glomerulonephritis. Studies in rodents demonstrate antiproteinuric and vasculoprotective effects of carnosine, the precise molecular mechanisms, however, are still incompletely understood. Thus, carnosinemia due to CN1 deficiency may be a non-disease; in contrast, carnosine may potentially protect against long-term sequelae of reactive metabolites accumulating, e.g. in diabetes and chronic renal failure.

Aminoacidopathies: Prevalence, Etiology, Screening, and Treatment Options

Inborn errors of metabolism (IEMs) are a group of inherited metabolic disorders which are caused by mutations in the specific genes that lead to impaired proteins or enzymes production. Different metabolic pathways are perturbed due to the deficiency or lack of enzymes. To date, more than 500 IEMs have been reported with most of them being untreatable. However, fortunately 91 such disorders are potentially treatable, if diagnosed at an earlier stage of life. IEMs have been classified into different categories and one class of IEMs, characterized by the physiological disturbances of amino acids is called as aminoacidopathies. Out of 91 treatable IEM, thirteen disorders are amino acid related. Aminoacidopathies can be detected by chromatography and mass spectrometry based analytical techniques (e.g., HPLC, GC-MS, LC-MS/MS) for amino acid level changes, and through genetic assays (e.g., PCR, TaqMan Genotyping, DNA sequencing) at the mutation level in the corresponding genes. Hence, this review is focused to describe thirteen common aminoacidopathies namely: Phenylketonuria (PKU), Maple Syrup Urine Disease (MSUD), Homocystinuria/Methylene Tetrahydrofolate Reductase (MTHFR) deficiency, Tyrosinemia type II, Citrullinemia type I and type II, Argininosuccinic aciduria, Carbamoyl Phosphate Synthetase I (CPS) deficiency, Argininemia (arginase deficiency), Hyperornithinemia-Hyperammonemia-Homocitrullinuria (HHH) syndrome, N-Acetylglutamate Synthase (NAGS) deficiency, Ornithine Transcarbamylase (OTC) deficiency, and Pyruvate Dehydrogenase (PDH) complex deficiency. Furthermore, the etiology, prevalence and commonly used analytical techniques for screening of aminoacidopathies are briefly described. This information would be helpful to researchers and clinicians especially from developing countries to initiate newborn screening programs for aminoacidopathies.

Methylmalonic acidemia (MMA) in pregnancy: a case series and literature review

INTRODUCTION

Women with inherited metabolic disorders, including those with previously life-limiting conditions such as MMA, are reaching child-bearing age more often due to advances in early diagnosis and improved pediatric care. Information surrounding maternal and fetal complications associated with the underlying disorders remains largely unexplored.

METHODS

Pregnancies affected by maternal MMA were ascertained through study 04-HG-0127 "Clinical and Basic Investigations of Methylmalonic Acidemia and Related Disorders" (clinicaltrials.gov identifier: NCT00078078) and via literature review. Prenatal and delivery records in study participants were reviewed.

RESULTS

Seventeen pregnancies were identified in women with isolated MMA, including three abortions, one termination, and 13 completed pregnancies [three cases with cblA (four pregnancies), four cases of mut- (one cobalamin responsive, three non-responsive), five cases with unknown type of MMA]. Seventeen percent (3/17) of the pregnancies resulted in a first trimester abortion, while 38.5% (5/13) of the completed pregnancies resulted in preterm deliveries. A cesarean delivery rate of 53.8% (7/13) was noted among the cohort. Fetal distress or nonreassuring fetal status was the indication for 57% (4/7) cesarean deliveries. One patient was reported to have metabolic crisis as well as episodes of mild hyperammonemia. Malformations or adverse outcomes in the progeny were not observed.

CONCLUSION

Although there have been a small number of pregnancies identified in women with MMA, the cumulative results suggest that the majority of pregnancies can be complicated by cesarean delivery and increased risk of prematurity. A pregnancy registry could clarify perinatal complications and define management approaches needed to ensure optimal maternal and fetal outcomes in this growing patient population.

Predictors of survival in children with methymalonic acidemia with homocystinuria in Beijing, China: a prospective cohort study

OBJECTIVE

(i) To determine whether clinical features and biochemical parameters help to predict survival of methylmalonic acidemia with homocystinuria; (ii) To find the cutoff values of biochemical parameters for predicting survival of methylmalonic acidemia with homocystinuria.

DESIGN

A prospective cohort study.

SETTING

A pediatric tertiary hospital in Beijing; all patients were followed until death or June 2013.

SUBJECTS

45 pediatric patients diagnosed with methylmalonic acidemia with homocystinuria between 2006 and 2012.

OUTCOME MEASURES

The data of clinical characteristics and pretreatment biochemical parameters were collected. The Cox regression analysis was performed to identify independent risk factors for survival of patients with methylmalonic acidemia and homocystinuria. The best cutoff values for these independent factors were determined by the receiver characteristic curve.

RESULTS

Newborn onset (OR=6.856, 95%CI=2.241-20.976, P=0.001), high level of methylmalonic acid in urine (OR=1.022, 95%CI=1.011-1.033, P<0.001), and high level of urea in serum (OR=1.083, 95%CI=1.027-1.141, P=0.003) were independent negative risk factors for survival of patients with methylmalonic acidemia and homocystinuria. The cutoff values of maximum predictive accuracy of methylmalonic acid in urine and urea in serum were respectively 5.41 mmol/mmol creatinine and 7.80 mmol/L by receiver operating characteristic curve analysis.

CONCLUSIONS

The patients of methylmalonic acidemia with homocystinuria tend to have an adverse outcome if they have newborn onsets. Elevated urea and urinary methylmalonic acid are predictors of adverse outcomes for the patients. They show similar effect for predicting severe adverse prognosis. The combination of methylmalonic acid in urine concentration and urea in serum concentration provided the most accurate predictive tool.

Systematic review and meta-analysis to estimate the birth prevalence of five inherited metabolic diseases

Many newborn screening programmes now use tandem mass spectrometry in order to screen for a variety of diseases. However, countries have embraced this technology with a differing pace of change and for different conditions. This has been facilitated by the ability of this diagnostic method to limit analysis to specific metabolites of interest, enabling targeted screening for particular conditions. MS/MS was introduced in 2009 in England to implement newborn bloodspot screening for medium chain acyl-CoA dehydrogenase deficiency (MCADD) raising the possibility of screening for other inherited metabolic disorders. Recently, a pilot screening programme was conducted in order to evaluate the health and economic consequences of screening for five additional inherited metabolic disorders in England. As part of this study we conducted a systematic review and meta-analysis to estimate the birth prevalence of these conditions: maple syrup urine disease, homocystinuria (pyridoxine unresponsive), glutaric aciduria type I, isovaleric acidaemia and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency including trifunctional protein deficiency. We identified a total of 99 studies that were able to provide information on the prevalence of one or more of the disorders. The vast majority of studies were of screening programmes with some reporting on clinically detected cases.

3-Methylglutaconic aciduria--lessons from 50 genes and 977 patients

Elevated urinary excretion of 3-methylglutaconic acid is considered rare in patients suspected of a metabolic disorder. In 3-methylglutaconyl-CoA hydratase deficiency (mutations in AUH), it derives from leucine degradation. In all other disorders with 3-methylglutaconic aciduria the origin is unknown, yet mitochondrial dysfunction is thought to be the common denominator. We investigate the biochemical, clinical and genetic data of 388 patients referred to our centre under suspicion of a metabolic disorder showing 3-methylglutaconic aciduria in routine metabolic screening. Furthermore, we investigate 591 patients with 50 different, genetically proven, mitochondrial disorders for the presence of 3-methylglutaconic aciduria. Three percent of all urine samples of the patients referred showed 3-methylglutaconic aciduria, often in correlation with disorders not reported earlier in association with 3-methylglutaconic aciduria (e.g. organic acidurias, urea cycle disorders, haematological and neuromuscular disorders). In the patient cohort with genetically proven mitochondrial disorders 11% presented 3-methylglutaconic aciduria. It was more frequently seen in ATPase related disorders, with mitochondrial DNA depletion or deletion, but not in patients with single respiratory chain complex deficiencies. Besides, it was a consistent feature of patients with mutations in TAZ, SERAC1, OPA3, DNAJC19 and TMEM70 accounting for mitochondrial membrane related pathology. 3-methylglutaconic aciduria is found quite frequently in patients suspected of a metabolic disorder, and mitochondrial dysfunction is indeed a common denominator. It is only a discriminative feature of patients with mutations in AUH, TAZ, SERAC1, OPA3, DNAJC19 TMEM70. These conditions should therefore be referred to as inborn errors of metabolism with 3-methylglutaconic aciduria as discriminative feature.

The incidence of urea cycle disorders

A key question for urea cycle disorders is their incidence. In the United States two UCDs, argininosuccinic synthetase and lyase deficiency, are currently detected by newborn screening. We used newborn screening data on over 6million births and data from the large US and European longitudinal registries to determine how common these conditions are. The incidence for the United States is predicted to be 1 urea cycle disorder patient for every 35,000 births presenting about 113 new patients per year across all age groups.

Aminoacidopathies and organic acidurias in Tunisia: a retrospective survey over 23 years

BACKGROUND

Inborn errors of metabolism are neglected in developing countries because they are not as common as infectious and nutritional disorders. In Tunisia, no information is available on the incidence and epidemiological features of these inherited metabolic diseases.

AIMS

To precise the profile of aminoacidopathies other than phenylketonuria and organic acidurias and to estimate their incidences in Tunisia.

METHODS

Between 1987 and 2009, our laboratory received 13171 requests for analysis of patients with symptoms suggestive of inborn errors of metabolism. For these cases, ion exchange chromatography of free amino acids was performed on amino acids analyser. Urinary organic acids profiles were determined by gas chromatography-mass spectrometry.

RESULTS

Abnormal cases were 370 (2.8%), divided into 212 cases of aminoacidopathies (57.3%) and 158 cases of organic acidurias (42.7%). The most frequent aminoacidopathies, were maple syrup disease (32.5%), tyrosinemia type I (28.8%) and nonketotic hyperglycinemia (16%). Methylmalonic aciduria (33.5%), propionic aciduria (18.4%) and 2-hyrdoxy glutaric aciduria (10.8%) were the most frequent organic acidurias. The incidences were calculated using the Hardy-Weinberg formula and were estimated at 1/13716 for maple syrup disease, 1/14804 for tyrosinemia type I, 1/16144 for methylmalonic aciduria and 1/23176 for propionic aciduria.

CONCLUSION

Aminoacidopathies and organic acidurias turned out to be highly frequent in Tunisia, mainly because of a high rate of consanguinity. We believe that they are underestimated. To improve their diagnosis, it is necessary to have available sophisticated equipment which would allow early treatment of patients.

Clinical, biochemical, and molecular analysis of combined methylmalonic acidemia and hyperhomocysteinemia (cblC type) in China

The most common inborn error of cobalamin (cbl) metabolism in China is the cblC type characterized by combined methylmalonic acidemia and hyperhomocysteinemia. The clinical presentation is relatively nonspecific, such as feeding difficulty, recurrent vomiting, hypotonia, lethargy, seizures, progressive developmental delay, and mental retardation, together with anemia and metabolic acidosis. More specific biochemical findings include high levels of propionylcarnitine (C3), free carnitine (C3/C0), and acetylcarnitine (C3/C2) measured by tandem mass spectrometry (MS/MS), elevation of methylmalonic acid (MMA) measured by gas chromatography-mass spectrometry (GC-MS), and increased total homocysteine with normal or decreased methionine. We report on 50 Chinese patients with combined methylmalonic acidemia and hyperhomocysteinemia. Forty-six belonged to the cblC complementation group. Mutation analysis of the MMACHC gene was performed to characterize the mutational spectrum of cblC deficiency, and 17 different mutations were found. Most were clustered in exons 3 and 4, accounting for 91.3% of all mutant alleles. Two mutations were novel, namely, c.315 C>G (p.Y105X) and c.470 G>C(p.W157S). In terms of genotype-phenotype correlation, the c.609 G>A mutation was associated with early-onset disease when homozygous. Unlike previous reports from other populations, c.609 G>A (p.W203X) was the most frequent cblC mutation detected in our study of Chinese patients, affecting 51 of 92 MMACHC alleles (55.4%). The high prevalence of this nonsense mutation could have potential therapeutic significance for Chinese cblC patients. Besides traditional approaches consisting of hydroxocobalamin injections, carnitine, betaine, and protein restriction, novel drugs that target premature termination codons may have a role in the future.

Glutaric aciduria type 1 in South Africa-high incidence of glutaryl-CoA dehydrogenase deficiency in black South Africans

Glutaric Aciduria type 1 (GA 1) is an inherited disorder of lysine and tryptophan catabolism that typically manifests in infants with acute cerebral injury associated with intercurrent illness. We investigated the clinical, biochemical and molecular features in 14 known GA 1 patients in South Africa, most of whom were recently confirmed following the implementation of sensitive urine organic acid screening at our laboratory. Age at diagnosis ranged from 3days to 5years and poor clinical outcome reflected the delay in diagnosis in all but one patient. Twelve patients were unrelated black South Africans of whom all those tested (n=11) were found homozygous for the same A293T mutation in the glutaryl-CoA dehydrogenase (GCDH) gene. Excretion of 3-hydroxyglutarate (3-OHGA) was >30.1μmol/mmol creatinine (reference range <2.5) in all cases but glutarate excretion varied with 5 patients considered low excretors (glutarate <50μmol/mmol creatinine). Fibroblast GCDH activity was very low or absent in all of five cases tested. Heterozygosity for the A293T mutation was found 1 in 36 (95% CI; 1/54 - 1/24) unrelated black South African newborns (n=750) giving a predicted prevalence rate for GA 1 of 1 in 5184 (95% CI; 1/11664 - 1/2304) in this population. GA 1 is a treatable but often missed inherited disorder with a previously unrecognised high carrier frequency of a single mutation in the South African black population.

Prediction of outcome in isolated methylmalonic acidurias: combined use of clinical and biochemical parameters

Objectives Isolated methylmalonic acidurias (MMAurias) are caused by deficiency of methylmalonyl-CoA mutase or by defects in the synthesis of its cofactor 5'-deoxyadenosylcobalamin. The aim of this study was to evaluate which parameters best predicted the long-term outcome. Methods Standardized questionnaires were sent to 20 European metabolic centres asking for age at diagnosis, birth decade, diagnostic work-up, cobalamin responsiveness, enzymatic subgroup (mut(0), mut(-), cblA, cblB) and different aspects of long-term outcome. Results 273 patients were included. Neonatal onset of the disease was associated with increased mortality rate, high frequency of developmental delay, and severe handicap. Cobalamin non-responsive patients with neonatal onset born in the 1970s and 1980s had a particularly poor outcome. A more favourable outcome was found in patients with late onset of symptoms, especially when cobalamin responsive or classified as mut(-). Prevention of neonatal crises in pre-symptomatically diagnosed newborns was identified as a protective factor concerning handicap. Chronic renal failure manifested earlier in mut(0) patients than in other enzymatic subgroups. Conclusion Outcome in MMAurias is best predicted by the enzymatic subgroup, cobalamin responsiveness, age at onset and birth decade. The prognosis is still unfavourable in patients with neonatal metabolic crises and non-responsiveness to cobalamin, in particular mut(0) patients.

Long-term needs of adult patients with organic acidaemias: outcome and prognostic factors

BACKGROUND

With improvements in the treatment of children with organic acidaemias (OA), the number surviving to adulthood is increasing. To plan appropriate services for their care it is important to know what their needs are.

OBJECTIVE

To describe the clinical and social problems affecting adult patients with OA.

PATIENTS AND METHODS

We reviewed the medical records of 15 adult patients diagnosed with OA. Social attainment (housing, schooling and occupation) was analysed. Nutritional status was evaluated by body mass index (BMI) and laboratory studies. Neurological and visceral complications were noted. Cognitive outcome was evaluated by psychometric testing and/or educational attainment.

RESULTS

Seven had methylmalonic acidaemia (MMA), 4 isovaleric acidaemia (IVA) and 4 propionic acidaemia (PA). Ten were female, and median age was 23.5 years (range 18-48). All but three had late-onset disease. Two patients became pregnant during follow up. Four patients had obtained university degrees and were working. Three-quarters of the patients required some kind of social support. All had a good nutritional status. Height was normal in IVA and 3 PA patients. Osteoporosis was present in 2 out of 8 patients assessed. A variety of neurocognitive or visceral complications were seen in two-thirds of the patients. Metabolic decompensations were unusual.

CONCLUSIONS

The approach to adult patients with OA has to be multidisciplinary, with the clinician and dietician as the core of the team, but with the collaboration of clinical nurses specialists, social workers and other specialist services and the support of a biochemical and molecular laboratory.

Hereditary urea cycle diseases in Finland

AIM

To estimate the incidence of urea cycle diseases (UCDs) in Finland and determine the course of the various disorders as well as the outcome.

METHODS

The original data were collected in the years 1998-2001. The diagnoses made after 2001, as well as the current status of the patients, were updated by surveys in the spring of 2007.

RESULTS

We found a total of 55 cases of UCDs in Finland by 2007: 30 cases of ornithine transcarbamylase (OTC) deficiency, 20 of argininosuccinate lyase (ASL) deficiency, 3 of carbamyl phosphate synthetase (CPS-I) deficiency, 1 of type 1 citrullinaemia and 1 of argininaemia. The estimated total incidence of UCDs was 1:39 000. The incidences of individual disorders were: OTC deficiency 1:62 000, ASL deficiency 1:144 000, CPS deficiency 1:539 000 and citrullinaemia 1:1 616 000. Eighteen (33%) of the patients with a diagnosis of UCD have died, most during their first hyperammonaemic crisis. One patient with OTC deficiency has had a liver transplant. Neurological symptoms of varying severity are common among these patients, particularly those with ASL deficiency.

CONCLUSION

The first survey on the incidence of UCDs in Finland shows some differences in the occurrence rates compared to other countries. Hyperammonaemia, and the neurological symptoms caused by it, can be avoided in most patients with late-onset UCDs with a standard treatment. However, in patients with ASL deficiency, the development of neurological symptoms seems to be inevitable in spite of careful treatment and avoidance of hyperammonaemia.

Diagnosis, symptoms, frequency and mortality of 260 patients with urea cycle disorders from a 21-year, multicentre study of acute hyperammonaemic episodes

AIM

A large longitudinal interventional study of patients with a urea cycle disorder (UCD) in hyperammonaemic crisis was undertaken to amass a significant body of data on their presenting symptoms and survival.

METHODS

Between 1982 and 2003, as part of the FDA approval process, data were collected on patients receiving an intravenous combination of nitrogen scavenging drugs (Ammonul sodium phenylacetate and sodium benzoate (10%, 10%)) for the treatment of hyperammonaemic crises caused by urea cycle disorders.

RESULTS

A final diagnosis of a UCD was made for 260 patients, representing 975 episodes of hospitalization. Only 34% of these patients presented within the first 30 days of life and had a mortality rate of 32%. The most common presenting symptoms were neurological (80%), or gastrointestinal (33%). This cohort is the largest collection of patients reported for these diseases and the first large cohort in the United States.

CONCLUSION

Surprisingly, the majority (66%) of patients with heritable causes of hyperammonaemia present beyond the neonatal period (>30 days). Patients with late-onset presenting disorders exhibited prolonged survival compared to the neonatal-presenting group.

Cross-sectional multicenter study of patients with urea cycle disorders in the United States

Inherited urea cycle disorders comprise eight disorders (UCD), each caused by a deficiency of one of the proteins that is essential for ureagenesis. We report on a cross-sectional investigation to determine clinical and laboratory characteristics of patients with UCD in the United States. The data used for the analysis was collected at the time of enrollment of individuals with inherited UCD into a longitudinal observation study. The study has been conducted by the Urea Cycle Disorders Consortium within the Rare Diseases Clinical Research Network (RDCRN) funded by the National Institutes of Health. One-hundred eighty-three patients were enrolled into the study. Ornithine transcarbamylase (OTC) deficiency was the most frequent disorder (55%), followed by argininosuccinic aciduria (16%) and citrullinemia (14%). Seventy-nine percent of the participants were white (16% Latinos), and 6% were African American. Intellectual and developmental disabilities were reported in 39% with learning disabilities (35%) and half had abnormal neurological examination. Sixty-three percent were on a protein restricted diet, 37% were on Na-phenylbutyrate and 5% were on Na-benzoate. Forty-five percent of OTC deficient patients were on L-citrulline, while most patients with citrullinemia (58%) and argininosuccinic aciduria (79%) were on L-arginine. Plasma levels of branched-chain amino acids were reduced in patients treated with ammonia scavenger drugs. Plasma glutamine levels were higher in proximal UCD and in neonatal type disease. The RDCRN allows comprehensive analyses of rare inherited UCD, their frequencies and current medical practices.

High incidence of hypermethioninaemia in a single neonatal intensive care unit detected by a newly introduced neonatal screening programme

From 1 January 2007 an expanded neonatal screening programme was initiated in the Netherlands, including homocystinuria with methionine as the primary marker. During the first 2 months hypermethioninaemia was detected in 14 newborns who, after proper evaluation, were demonstrated not to have classical homocystinuria. Remarkably, all these children were admitted to a single neonatal intensive care unit (Academic Medical Center, Amsterdam (AMC-NICU)). We evaluated the possible causes for this finding. The cohort of newborns with hypermethioninaemia (group 1) was compared with the cohort of newborns with normal screening results admitted to the AMC-NICU in the same time period (group 2). In addition, parenteral nutrition protocols from all NICUs in the Netherlands were compared. Mean birth weight and gestational age were significantly lower in group 1 than in group 2. All patients in group 1 received parenteral feeding (TPN) at the time of screening and received a higher mean amino acid intake per kilogram body weight than patients receiving TPN in group 2. Also, the AMC-NICU uses a different amino acid mixture for TPN than the other Dutch NICUs, containing more than twice the amount of methionine per gram of amino acids compared with other mixtures. The high incidence of hypermethioninaemia in the AMC-NICU is explained by a combination of low birth weight, low gestational age, and high protein intake supplied by a specific parenteral amino acid mixture containing large amounts of methionine. To prevent hypermethioninaemia, the use of high-methionine containing solutions for TPN should be reconsidered.

Different spectrum of mutations of isovaleryl-CoA dehydrogenase (IVD) gene in Korean patients with isovaleric acidemia

Isovaleric acidemia (IVA) is an autosomal recessive inborn error of the leucine metabolism that is caused by a deficiency of isovaleryl-CoA dehydrogenase (IVD). Recent application of tandem mass spectrometry to newborn screening has allowed a significant expansion of the recognition of individuals with IVD deficiency. Although many patients have been reported worldwide, there are no genetically confirmed patients in Korea. This study characterizes IVD mutations in seven Korean IVA patients from six unrelated families. Bi-directional sequencing analysis identified two novel variations affecting consensus splice sites (c.144+1G>T in intron 1 and c.457-3_2CA>GG in intron 4) and three novel variations altering coding sequences (c.149G>T; Arg21Leu, c.832A>G; Ser249Gly, and c.1135T>G; Phe350Val). Five patients from four families were found to be compound heterozygotes while two unrelated patients were homozygous for the c.457-3_2CA>GG variation. Reverse-transcription polymerase chain reaction confirmed that both intron variations cause aberrant splicing. Furthermore, analysis of cultured lymphocyte extracts of the seven patients showed no detectable enzyme activity and reduced levels of IVD protein (<10.0% of control) in all samples. These results confirm IVD mutations in Korean patients with IVA and reveal that the mutation spectrum is different from previously reported patients.

Prolonged QTc intervals and decreased left ventricular contractility in patients with propionic acidemia

OBJECTIVE

To investigate electrophysiological and functional signs of myocardial damage in patients with propionic acidemia (PA), an inborn error of metabolism caused by deficiency of propionyl CoA carboxylase (PCC).

STUDY DESIGN

In an observational longitudinal study 10 patients with PA (6 boys and 4 girls) ranging between 2.5 and 20.2 (median 9.0) years of age at last follow-up were investigated over a period of up to 20 (mean 7.4) years using 12-lead electrocardiograms (ECGs), 24-hour continuous ECG recordings, bicycle exercise testings, and echocardiography with special focus on repolarization abnormalities such as corrected QT interval (QTc) prolongation, ventricular dysrhythmias, and left ventricular systolic function.

RESULTS

QTc interval was prolonged (>440 ms) in 70% of patients beyond infanthood. Continuous ECG recordings revealed rhythm disturbances in 20% of patients. M-mode echocardiographic left ventricular function was reduced (fractional shortening [FS] <30%) in 40%. One patient showed signs of dilated cardiomyopathy.

CONCLUSIONS

The majority of patients with PA (even in clinically stable situations) have disturbances in cardiac electrophysiology that can contribute to cardiac complications. Possible mechanisms include effects of toxic metabolites or deprivation of essential substrates. To avoid life-threatening complications, we recommend regular cardiological evaluations in this group of patients.

Clinical and biochemical studies on Chinese patients with methylmalonic aciduria

Methylmalonic aciduria is a common organic aciduria disease. Recently, gas chromatography-mass spectrometry has been used to diagnose methylmalonic aciduria in China. Often, however, the diagnosis of methylmalonic aciduria is delayed because of a lack of technical expertise and the limited experience of general clinicians in China. In this study, the natural history, clinical features, and outcome of 77 Chinese patients with methylmalonic aciduria were investigated. Of the 77 patients, 31 (40.3%) had isolated methylmalonic aciduria and 46 (59.7%) had methylmalonic aciduria combined with homocystinemia. Thus, we observed a higher rate of the combined disease than studies conducted in other countries, suggesting that it might be more common in China. Total plasma homocysteine measurement might enable differential diagnoses of methylmalonic aciduria to be distinguished. The clinical spectrum of these 77 patients with methylmalonic aciduria ranged from neonatal death and severe symptoms to benign asymptomatic organic aciduria. Neonatal and infantile onset, which was a characteristic of the majority of cases, was associated with a greater severity relative to later-onset cases. Among the 17 cases who had onset after 3 years of age, only 1 patient had isolated methylmalonic aciduria and 16 had combined methylmalonic aciduria and homocystinemia. Nine of the patients with combined methylmalonic aciduria and homocystinemia completely recovered and exhibited normal intelligence, whereas seven improved, with a mild handicap.

New splicing mutations in propionic acidemia

Propionic acidemia results from mutations in either of the two genes, PCCA or PCCB, that encode the two subunits of the propionyl-CoA carboxylase (PCC) enzyme. In this study, we report the identification and analysis of seven novel splicing mutations involving consensus donor and acceptor splice sites. Most of them were identified in patients with a Central Asian origin, and some present in several alleles, probably reflecting founder effects. The functional consequences of the splicing mutations were analyzed in patients' fibroblasts, as well as transcript quantification using real-time PCR methods. In the PCCA gene, two mutations were demonstrated to affect 5' splice sites (c.231+1G>C and c.1209+3A>G) and two 3' acceptor splice sites (c.1210delG and c.1430G>T), all causing skipping of the exons involved, with no detectable levels of normally spliced transcript. In the PCCB gene, all three mutations involved 5' donor splice sites-two affected exon 1 splicing (c.154_183+17del46 and c.183+2T>C), the latter activating a cryptic splice site in intron 1, and the remaining mutation (c.1498+2T>C) resulted in exon 14 skipping. The results highlight the necessity to perform transcript analysis in addition to genomic DNA sequencing to characterize the effect of splicing mutations and add relevant information on the genetic epidemiology of the disease.

Glutaric acidemia type 1 in patients of Lumbee heritage from North Carolina

Glutaric acidemia type I (GA-I) is an autosomal recessive disorder of the catabolism of lysine, hydroxylysine, and tryptophan caused by deficiency of glutaryl-CoA dehydrogenase (GCD). Among our patients with GA-I, we noted a prevalence of Lumbee individuals. The Lumbee are a close-knit Native American tribe of eastern North Carolina. Five Lumbee individuals with GA-I had homozygous 1240G>A mutations in GCD. This is a rare, known mutation that was likely introduced by a Lumbee founder.

Retrospective study of patients with suspected inborn errors of metabolism at Siriraj Hospital, Bangkok, Thailand (1997-2001)

INTRODUCTION

This retrospective clinical study was carried out on patients with suspected inborn errors of metabolism (IEM) at Siriraj Hospital during 1997-2001. The authors investigated 114 patients by quantitative plasma amino acid analysis.

OBJECTIVE

The objective of this study was to collect and analyze epidemiologic and specific clinical data of IEM, especially in small-molecule diseases.

MATERIAL AND METHOD

All patients were categorized into 2 major groups. 1) positive diagnoses for IEM 2) negative diagnoses for IEM. The two groups were investigated, studied including statistical analysis.

RESULTS

The authors found that most IEM ascertained through plasma amino acid analysis were small-molecule diseases (74.3%) and amino acid disorders consisted of the most frequent disorders. The presented data demonstrated that the ratio of positive diagnoses to all patients studied was 1:8. Epidemiological data showed there were more male than female patients. Onset of diseases occurred predominantly during the first month of age, and was rarely found after 3 years of age. There were histories of consanguinity in half of the IEM patients. The most common presenting symptom was acute metabolic encephalopathy and specific signs for small-molecule disorders included hepatomegaly, unusual urine odor, acidosis, hyperammonemia, alteration of consciousness, and ketosis/ketonuria. These signs or symptoms indicated further metabolic investigations.

CONCLUSION

Comparison of the data from Thailand with other countries showed both similarities and differences to the Caucasian population. Thus, further studies in IEM are much needed for the Thai population.

Amino Acid Disorders in Mental Retardation: A Two-Decade Study from Andhra Pradesh

A screening program was carried out for amino acid disorders in children with mental handicaps from the state of Andhra Pradesh (India) during the last two decades. Forty-one (0.9%) cases were detected with amino acid disorders among 4500 children surveyed. We reported amino acid disorders of rare occurrence such as dicarboxylic aminoaciduria, hydroxykynureninuria, persistent hypertyrosinemia, hydroxyprolinemia, hypervalinemia, etc. A new metabolic defect threoninemia was also detected. We have observed a preponderance of males with amino acid disorders. Parental consanguinity was present in 54% of cases with amino acid disorders.

Frequencies of inherited organic acidurias and disorders of mitochondrial fatty acid transport and oxidation in Germany

The lack of epidemiological data on the frequency and/or burden of organic acidurias (OA) and mitochondrial fatty acid transport and oxidation disorders (mtFATOD) is one reason for hesitation to expand newborn screening (NBS) by tandem mass spectrometry (MS-MS). From 1999 to 2000, the frequency of ten potentially treatable OA and mtFATOD was assessed by active nation-wide surveillance on cases presenting with clinical symptoms using the German Paediatric Surveillance Unit (ESPED) system. Case ascertainment was complemented by a second independent source: 3-monthly inquiries in the metabolic laboratories performing secondary selected screening for OA and mtFATOD. Frequency estimates for clinically symptomatic cases older than 7 days in a birth cohort of 844,575 conventionally screened children was compared to the frequency found in a cohort of 382,247 screened by MS-MS in Bavaria and Baden-Württemberg. The overall frequency of the ten conditions considered was 1:8,000 (95% CI 1:11,000-1:6,000) by MS-MS as compared to 1:23,000 (95% CI 1:36,000-1:17,000) in symptomatic cases presenting mainly with metabolic crisis. The contributions of medium-chain acyl-CoA dehydrogenase deficiency (MCADD), other mtFATOD and OA were 29, 4 and 13 among the 46 cases identified by MS-MS, and 19, 1 and 13 among the 33 clinically symptomatic cases, respectively. Acute metabolic crisis, with a lethal outcome in four patients, was reported for 22/33 clinically symptomatic cases. No clinically symptomatic cases were reported from cohorts with screened by MS-MS.

CONCLUSION

ten potentially treatable organic acidurias and mitochondrial fatty acid transport and oxidations disorders were more common than phenylketonuria with organic acidurias accounting for 28% of the cases detected by newborn screening and 39% of the cases identified on high risk screening. These conditions were related to considerable morbidity and mortality. Considerations for their inclusion in expanded newborn screening programmes might be warranted.

Glutaric aciduria type I: outcome in the Republic of Ireland

Twenty-one patients have been diagnosed with glutaric aciduria type I over a 16-year period in the Republic of Ireland, 11 following clinical presentation and 10 following a high-risk screen. Nineteen have been managed with diet. Eight patients have died, of whom 7 were diagnosed clinically. Six had dystonic and one spastic cerebral palsy. Of the 11 patients who did not have cerebral palsy, 10 were diagnosed following a high-risk screen. Seven of the 11 have no abnormal neurological signs; 6 of the 7 have abnormal CT or MRI findings; and no case of striatal degeneration has occurred during the past 14 years in the high-risk screened group.

Neonatal screening for glutaryl-CoA dehydrogenase deficiency

Acute encephalopathic crisis in glutaryl-CoA dehydrogenase deficiency results in an unfavourable disease course and poor outcome, dominated by dystonia, feeding problems, seizures and secondary complications, and quite often leading to early death. The prerequisite for the prevention of irreversible brain damage in this disease is the detection of affected patients and initiation of treatment before the manifestation of such crisis. Apart from macrocephaly there are no signs or symptoms characteristic for this disease in presymptomatic children and, thus, they are usually missed. In some countries, implementation of extended neonatal screening programmes using electrospray ionization tandem mass spectrometry (ESI-MS/MS) allows detection of affected newborns and start of therapy before onset of neurological complications. This article summarizes recent strategies, pitfalls and shortcomings of a mass screening for glutaryl-CoA dehydrogenase deficiency using ESI-MS/MS. Furthermore, an alternative strategy, namely DNA-based neonatal screening for the Oji-Cree variant of this disease, is demonstrated. An optimization of diagnostic as well as therapeutic procedures must be achieved before GCDH deficiency unequivocally fulfills the criteria of a reliable and successful newborn screening programme.