AGAT<unk>  can be suspected from clinical findings, although there is significant phenotypic overlap with the most common presenting symptoms of intellectual disability and muscle weakness. Laboratory testing of plasma and urine will show decreased levels of creatine and guanidinoacetate. Non-specific elevations of metabolites on urine testing that are normalized to creatinine may appear falsely elevated. Magnetic resonance spectroscopy (MRS) of the brain will also show an absence of creatine, which is normally present. This finding is not specific to AGAT<unk> , it can be observed in all three cerebral creatine<unk> es. The combination of biochemical testing and MRS findings can be strongly suggestive of AGAT<unk> . Confirmation would most often be done with molecular testing of GATM. Identification of biallelic pathogenic variants in GATM would be confirmation of a diagnosis of AGAT<unk> . Uncertain findings on molecular testing may be able to be confirmed by enzyme assays, or by measuring creatine uptake in fibroblasts. Prenatal testing for AGAT<unk>  can be performed on chorionic villi samples if the causative pathogenic variants in the family are known.
Arginine:glycine amidinotransferase deficiency
Galactose-1-phosphate uridylyltransferase deficiency
Ornithine aminotransferase deficiency
Ribose-5-phosphate isomerase deficiency
Aminoacylase 1 deficiency
Malonyl-CoA decarboxylase deficiency
Carbamoyl phosphate synthetase I deficiency
Guanidinoacetate methyltransferase deficiency