title: A pilot study to estimate incidence of guanidinoacetate methyltransferase deficiency in newborns by direct sequencing of the GAMT gene.
abstract: BACKGROUND
  GAMT deficiency is an autosomal recessive disorder of creatine biosynthesis causing developmental delays or intellectual disability in untreated patients as a result of irreversible brain damage occurring prior to diagnosis. Normal neurodevelopmental outcome has been reported in patients treated from neonatal period highlighting the importance of early treatment.
  
  
  METHODS
  Five hundred anonymized newborns from the National Newborn Screening Program of The Netherlands were included into this pilot study. Direct sequencing of the coding region of the GAMT gene was applied following DNA extraction. The disease causing nature of novel missense variants in the GAMT gene was studied by overexpression studies. GAA and creatine was measured in blood dot spots.
  
  
  RESULTS
  We detected two carriers, one with a known common (c.327G>A) and one with a novel mutation (c.297_309dup (p.Arg105Glyfs*) in the GAMT gene. The estimated incidence of GAMT deficiency was 1:250,000. We also detected five novel missense variants. Overexpression of these variants in GAMT deficient fibroblasts did restore GAMT activity and thus all were considered rare, but not disease causing variants including the c.131G>T (p.Arg44Leu) variant. Interestingly, this variant was predicted to be pathogenic by in silico analysis. The variants were included in the Leiden Open Variation Database (LOVD) database (www.LOVD.nl/GAMT). The average GAA level was 1.14μmol/L±0.45 standard deviations. The average creatine level was 408μmol/L±106. The average GAA/creatine ratio was 2.94±0.136.
  
  
  CONCLUSIONS
  The estimated incidence of GAMT deficiency is 1:250,000 newborns based on our pilot study. The newborn screening for GAMT deficiency should be implemented to identify patients at the asymptomatic stage to achieve normal neurodevelopmental outcome for this treatable neurometabolic disease. Biochemical investigations including GAA, creatine and GAMT enzyme activity measurements are essential to confirm the diagnosis of GAMT deficiency. According to availability, all missense variants can be assessed functionally, as in silico prediction analysis of missense variants is not sufficient to confirm the pathogenicity of missense variants.
authors: Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, Canada; Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Canada. Electronic address: saadet.mahmutoglu@sickkids.ca.
authors: S
authors: S
authors: Mercimek-Mahmutoglu
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands.
authors: A
authors: A
authors: Pop
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands.
authors: W
authors: W
authors: Kanhai
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands.
authors: M
authors: M
authors: Fernandez Ojeda
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands.
authors: U
authors: U
authors: Holwerda
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands.
authors: D
authors: D
authors: Smith
authors: National Institute for Public Health and the Environment, Centre for Infectious Diseases Research, and Screening, Bilthoven, The Netherlands.
authors: J G
authors: JG
authors: Loeber
authors: National Institute for Public Health and the Environment, Centre for Infectious Diseases Research, and Screening, Bilthoven, The Netherlands.
authors: P C J I
authors: PC
authors: Schielen
authors: Metabolic Unit, Department of Clinical Chemistry, VU Medical Center, Neurosciences Campus, Amsterdam, The Netherlands. Electronic address: g.salomons@vumc.nl.
authors: G S
authors: GS
authors: Salomons
mesh_terms: D030561:Databases, Nucleic Acid; D005260:Female; D050937:Guanidinoacetate N-Methyltransferase / Q000172:deficiency* / Q000235:genetics; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007805:Language Development Disorders / Q000453:epidemiology / Q000235:genetics*; D008297:Male; D008403:Mass Screening; D009069:Movement Disorders / Q000151:congenital* / Q000453:epidemiology / Q000235:genetics; D020125:Mutation, Missense; D010865:Pilot Projects
chemical_list: C494506:GAMT protein, human; D050937:Guanidinoacetate N-Methyltransferase
keywords: Creatine; Functional analysis; GAA; GAMT deficiency; Newborn blood spots; Newborn screening; Sanger sequencing