Urine creatine metabolism is monitored for the evaluation of patients with clinical suspicion of hereditary creatine metabolism disorders including arginine amidinotransferase deficiency: glycine and methyltransferase deficiency.
Disturbances in creatine synthesis (arginine amidinotransferase deficiency: glycine [AGAT], guanidinacetic acid methyltransferase deficiency [GAMT] and lack of creatine transporter synergism [SLC6A]. AGAT and GAMT deficiencies are inherited in an autosomal recessive manner, while creatine transporter disorders are interconnected. All three disorders result in a decrease in creatine in the brain and typically appear as developmental delay, mental retardation and severe speech delay. Patients with creatine deficiency syndrome usually have seizures. Patients with guanidinacetic acid methyltransferase deficiency and creatine transporter deficiency develop behavioral problems and autistic characteristics. Girls with a mutation in the creatine carrier deficiency may have mental retardation and behavioral problems, and some may even have seizures.
Creatine deficiency syndromes are diagnosed by measuring guanidinoacetic acid, creatine, and creatinine in plasma or urine. The results are specific to each clinical entity:
- Patients with GAMT deficiency usually show normal to low creatine, highly elevated guanidinoacetic acid and low creatinine.
- Patients with AGAT deficiency usually show normal to low creatine, low guanidinoacetic acid, and normal to low creatinine.
- Patients with SLC6A8 deficiency show increased creatinine, normal guanidinoacetic acid, normal to low creatinine and increased creatine: creatinine ratio.
Treatment for AGAT and GAMT deficiencies is by oral administration of creatine supplementation. Creatine intake does not appear to benefit boys with deficiency in the creatine carrier, whereas girls with a creatine carrier mutation benefit from creatine intake.
Before taking the sample (plasma & urine), supplements containing creatine should be discontinued.
See also: Creatine, Blood and Blood Creatine Metabolism Control, Urine Creatine
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