guanidinoacetate methyltransferase deficiency
Findings
No curated finding names guanidinoacetate methyltransferase deficiency yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
A creatine deficiency syndrome characterized by global developmental delay/intellectual disability (DD/ID), prominent speech delay, autistic/hyperactive behavioral disorders, seizures, and various types of pyramidal and/or extra-pyramidal manifestations.
Definition from the Mondo Disease Ontology (MONDO:0012999), read 2026-09-29. CC BY 4.0.
- Inheritance
- Autosomal recessive inheritance
- Onset and course
- Infantile onset
HPO, annotations 2026-09-02
Features
36 features
What the disease is reported to present with, and how often among people who have it — never how often a feature means the disease. HPO, annotations 2026-09-02.
- Decreased serum creatinineHPOHP:0012101
- 2 of 2 reported patients
- Elevated brain guanidinoacetate level by MRSHPOHP:6000484
- 1 of 1 reported patient
- Elevated circulating guanidinoacetic acid concentrationHPOHP:0034321
- 4 of 4 reported patients
- HypotoniaHPOHP:0001252
- 2 of 2 reported patients · Infantile onset
- Very rare (1% to 4% of cases)
- Reduced tissue guanidinoacetate methyltransferase activityHPOHP:6000722
- 4 of 4 reported patients
- Severe global developmental delayHPOHP:0011344
- 7 of 7 reported patients
- Frequent (30% to 79% of cases)
Show the remaining 24
- Progressive extrapyramidal movement disorderHPOHP:0007153
- Frequent (30% to 79% of cases)
- Absent speechHPOHP:0001344
- 2 of 5 reported patients
- Aggressive behaviorHPOHP:0000718
- 2 of 5 reported patients
- Occasional (5% to 29% of cases)
- Atonic seizureHPOHP:0010819
- 2 of 5 reported patients
- Occasional (5% to 29% of cases)
- RigidityHPOHP:0002063
- 2 of 5 reported patients
- Abnormal head movementsHPOHP:0002457
Genes
1 gene
Germline variants in the gene encoding each protein, as classified by GenCC submitters, each in their own words. Limited, disputed and refuted submissions are listed too.
- GAMTHGNC:4136
- Definitive · Ambry Genetics · Autosomal recessive · 2018
- Definitive · ClinGen · Autosomal recessive · 2019
- Definitive · G2P · Autosomal recessive · 2015
- Definitive · Natera · Autosomal recessive · 2023
- Strong · Labcorp Genetics (formerly Invitae) · Autosomal recessive · 2023
- Strong · PanelApp Australia · Autosomal recessive · 2025
- Supportive · Orphanet · Autosomal recessive · 2021
Where it sits
Other names
5 names
Resolves to: guanidinoacetate methyltransferase deficiency
- Also called
- cerebral creatine deficiency syndrome 2cerebral creatine deficiency syndrome type 2disorder of guanidinoacetate N-methyltransferase activityGAMT deficiencyguanidinoacetate N-methyltransferase activity disease