Dataset Information

Argininosuccinic Acid Lyase Deficiency Missed by Newborn Screen.

ABSTRACT: Argininosuccinic acid lyase (ASL) deficiency, caused by mutations in the ASL gene (OMIM: 608310) is a urea cycle disorder that has pleiotropic presentations. On the mild end, ASL deficiency can manifest as nonspecific neurocognitive abnormalities without readily identifiable signs to differentiate it from other causes of intellectual disability or learning disabilities. Dietary management and arginine supplementation, if initiated early, may ameliorate symptoms.Because of the nonspecific nature of the symptoms and the possibility for therapeutic management, ASL deficiency is part of the recommended uniform screening panel for newborn screening in the USA. We report here a case of ASL deficiency that was missed on newborn screening in the USA.The case reported here has two known pathogenic mutations - one with no residual activity and one with reported 10% residual activity. Review of this newborn screening results showed subtle elevation of citrulline, overlapping the normal range. These findings suggest that newborn screening may be missing other patients with ASL deficiency with at least one hypomorphic allele. This case was diagnosed incidentally, but in retrospect had symptoms best attributed in full or in part to his ASA deficiency, including protein aversion, developmental delay, and seizures. This case highlights the importance of considering ASL deficiency in patients with nonspecific abnormal neurocognitive signs, such as epilepsy and developmental delay, even when newborn screening was normal.

SUBMITTER: Ganetzky RD

PROVIDER: S-EPMC5509549 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Argininosuccinic Acid Lyase Deficiency Missed by Newborn Screen.

Ganetzky Rebecca D RD Bedoukian Emma E Deardorff Matthew A MA Ficicioglu Can C

JIMD reports 20160812

Argininosuccinic acid lyase (ASL) deficiency, caused by mutations in the ASL gene (OMIM: 608310) is a urea cycle disorder that has pleiotropic presentations. On the mild end, ASL deficiency can manifest as nonspecific neurocognitive abnormalities without readily identifiable signs to differentiate it from other causes of intellectual disability or learning disabilities. Dietary management and arginine supplementation, if initiated early, may ameliorate symptoms.Because of the nonspecific nature ...[more]

PMID: 27515243

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Project description:The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCD), a group of inborn errors of hepatic metabolism that often result in life threatening hyperammonemia. Argininosuccinate lyase (ASL) is a cytosolic enzyme which catalyzes the fourth reaction in the cycle and the first degradative step, that is, the breakdown of argininosuccinic acid to arginine and fumarate. Deficiency of ASL results in an accumulation of argininosuccinic acid in tissues, and excretion of argininosuccinic acid in urine leading to the condition argininosuccinic aciduria (ASA). ASA is an autosomal recessive disorder and is the second most common UCD. In addition to the accumulation of argininosuccinic acid, ASL deficiency results in decreased synthesis of arginine, a feature common to all UCDs except argininemia. Arginine is not only the precursor for the synthesis of urea and ornithine as part of the urea cycle but it is also the substrate for the synthesis of nitric oxide, polyamines, proline, glutamate, creatine, and agmatine. Hence, while ASL is the only enzyme in the body able to generate arginine, at least four enzymes use arginine as substrate: arginine decarboxylase, arginase, nitric oxide synthetase (NOS) and arginine/glycine aminotransferase. In the liver, the main function of ASL is ureagenesis, and hence, there is no net synthesis of arginine. In contrast, in most other tissues, its role is to generate arginine that is designated for the specific cell's needs. While patients with ASA share the acute clinical phenotype of hyperammonemia, encephalopathy, and respiratory alkalosis common to other UCD, they also present with unique chronic complications most probably caused by a combination of tissue specific deficiency of arginine and/or elevation of argininosuccinic acid. This review article summarizes the clinical characterization, biochemical, enzymatic, and molecular features of this disorder. Current treatment, prenatal diagnosis, diagnosis through the newborn screening as well as hypothesis driven future treatment modalities are discussed.

Project description:BackgroundNewborn screening (NBS) for medium chain acyl-CoA dehydrogenase deficiency (MCADD), one of the most common disorders identified, uses measurement of octanoylcarnitine (C8) from dried blood spots. In the state of Ohio, as in many places, primary care providers, with or without consultation from a metabolic specialist, may perform "confirmatory testing", with the final diagnostic decision returned to the state. Confirmatory testing may involve measurement of metabolites, enzyme analysis, mutation screening, or sequencing. We now report sequencing results for infants said to have "false positive" NBS results for MCAD deficiency, or who died before confirmatory testing could be performed.MethodsDried blood spots (DBS) were obtained from all 18 available NBS cards identified as "false positive" by NBS for the 3 year period after screening began in Ohio in 2003 (N=20, thus 2 had no DBS available), and from all 6 infants with abnormal screens who died before confirmatory testing could be obtained. DNA extracted from DBS was screened for the common c.985A>G mutation in exon 11 of the ACADM gene, using a specific restriction digest method, followed by sequencing of the 12 exons, intron-exon junctions, and several hundred base pairs of the 5' untranslated region.ResultsThe NBS cut-off value for C8 used was 0.7 μmol/L. Sequencing of ACADM in six neonates with elevated C8 on NBS who died before confirmatory testing was obtained did not identify any significant variants in the coding region of the gene, suggesting that MCADD was not a contributing factor in these deaths. The mean C8 for the 18 surviving infants labeled as "False Positives" was 0.90 (95%CI 0.77-1.15), much lower than the mean value for confirmed cases. Ten of the 18 were premature births weighing <1200 g, the rest were normal sized and full term. Eight infants, mostly full term with appropriate birth weight, were heterozygous for the common c.985A>G mutation; one of those also has a novel sequence change identified in exon 9 that predicts a PRO to LEU change at residue 258 of the protein. Both the phase and any possible clinical significance of the variant are unknown, but several lines of evidence suggest that it could lead to protein malfunction. That child had an NBS C8 of 2.2, more than double the mean for the False Positive group. Unfortunately, the study design did not provide clinical outcome data, but the child is not known to have presented clinically by age 7 years.ConclusionsThese results suggest that sequencing of ACADM from dried blood spots can be one useful follow-up tool to provide accurate genetic counseling in the situation of an infant with elevated C8 on NBS who dies before confirmatory testing is obtained. Of surviving neonates, there appear to be two populations of infants with false positive NBS C8 values: 1) term AGA infants who are heterozygous for the common c.985A>G mutation, and, 2) premature infants, regardless of carrier status. The finding of two sequence variants in an infant reported to the state as not affected suggests the possibility that some infants with two mutations may be reported as normal at follow-up. State registries may wish to consider asking that metabolic specialists, who are most familiar with the variability of these rare disorders, be involved in the final diagnostic evaluation. Finally, providers may wish to consider ACADM sequencing, or other diagnostic testing, as part of the confirmatory evaluation for infants with NBS C8 concentrations that are significantly above the cut-off value, even if plasma and urine metabolites are not strikingly increased.

Dataset Information

Argininosuccinic Acid Lyase Deficiency Missed by Newborn Screen.

Publications

Argininosuccinic Acid Lyase Deficiency Missed by Newborn Screen.

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