GTR Home > Conditions/Phenotypes > Deficiency of guanidinoacetate methyltransferase

Disease characteristics

Excerpted from the GeneReview: Creatine Deficiency Syndromes
The cerebral creatine deficiency syndromes (CCDS), inborn errors of creatine metabolism, include the two creatine biosynthesis disorders, guanidinoacetate methyltransferase (GAMT) deficiency and L-arginine:glycine amidinotransferase (AGAT or GATM) deficiency, and the creatine transporter (SLC6A8) deficiency. Intellectual disability and seizures are common to all three CCDS. The majority of individuals with GAMT deficiency have a behavior disorder that can include autistic behaviors and self-mutilation; a significant proportion have pyramidal/extrapyramidal findings. Onset is between ages three months and three years. Only seven individuals with AGAT deficiency have been reported. The phenotype of SLC6A8 deficiency in affected males ranges from mild intellectual disability and speech delay to severe intellectual disability, seizures, and behavior disorder; age at diagnosis ranges from two to 66 years. Females heterozygous for SLC6A8 deficiency may have learning and behavior problems.

Associated genes

Clinical features

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  • Hyperreflexia
  • Hypertonia
  • Intellectual disability
  • Seizure
  • Progressive extrapyramidal movement disorder
  • Delayed speech and language development
  • Ataxia
  • Global developmental delay
  • Myoclonus
  • Infantile muscular hypotonia
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