Aydin, Halil IbrahimSonmez, Fatma Mujgan2020-11-092020-11-0920190041-4301http://www.turkishjournalpediatrics.org/uploads/pdf_TJP_1943.pdfhttp://hdl.handle.net/11727/5019Guanidinoacetate methyltransferase (GAMT) deficiency is a rare autosomal recessive disorder of creatine biosynthesis. Here, we report 9 and 10-year-old cousins with GAMT deficiency caused by a novel mutation who both exhibited neurodevelopmental retardation, seizures, behavioral problems, and autism that began during early infancy. The patients were diagnosed as having only autism and followed for years without a specific diagnosis although they had very low levels of serum creatinine for several times. A novel nonsense mutation in the GAMT gene that caused cessation of synthesis of the protein encoded by this gene was identified in these patients. GAMT deficiency is a treatable inborn error of metabolism and should be considered for all patients with hypotonia, developmental delay, seizures and autism, particularly if low serum creatinine levels are observed.enginfo:eu-repo/semantics/openAccesscreatine deficiency syndromesguanidinoacetate methyltransferaseautismepilepsyarticle61192960004878559000142-s2.0-85072709548