Short-term and Long-term Follow-up 2 - Emerging Conditions (Get Ready!) Tuesday, Oct. 28 - 10:30am-12:00pm
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Background: The New England Newborn Screening Program (NENSP) has used low citrulline (Cit) as a biomarker to screen for the proximal UCDs [ornithine transcarbamylase (OTC), carbamylphosphate synthase (CPS) deficiency, and N-acetylglutamate synthase (NAGS)] since 2004. Low plasma Cit has been reported in other metabolic disorders (pyrroline-5-carboxylate synthetase deficiency -P5CS) and Cit is used as a marker of enterocytes mass and function. We performed a retrospective analysis to evaluate the (1) determine the etiology of the false positives (FP) and (2) possibility of screening for other disorders when using low Cit as a marker in screening. Methods: The study cohort is all 1.2 M newborns screened for the proximal UCD’s in the region from Aug 2004 to Aug 2013. Cit is analyzed as part of the amino acid and acylcarnitine markers analyzed by MS/MS. A positive screen for proximal UCDs were specimens with 1) Cit 3uM to < 3.8 in conjunction with Cit/[Tyr x Met] < 0.002. Results: In 20 infants the initial specimen collected by day of life 7 screened positive for a proximal UCD. Of these infants 8 were confirmed to have a proximal UCD (5 OTC, 2 CPS, and 1 NAGS). The other 12 were concluded to be FP. Nine FP were from neonates in intensive care units (NICU) on total parenteral nutrition (TPN).The 3 neonates with FP screens who were not in the NICU showed various plasma and/or clinical anomalies on follow-up. An additional 5 infants with in-range Cit values on an initial screen and a positive screen on a subsequent screen were identified; these were all infants who had had a bowel resection and were on TPN. The newborn screening data of the only infant with P5CS deficiency in the cohort was reviewed and was noted to have a low Cit (4.2 uM), albeit above our threshold. One
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