Urine creatine metabolism is performed for the evaluation of patients with clinical suspicion of hereditary creatine metabolism disorders including arginine amidinotransferase deficiency: glycine, guanidine acetic acid methyltransferase deficiency, and creatine transporter deficiency.
Disorders in creatine synthesis (arginine amidinotransferase: glycine deficiency [AGAT], guanidine acetic acid methyltransferase deficiency [GAMT], and lack of creatine transporter [SLC6A] collectively described as creatine deficiency syndromes. AGAT and GAMT deficiencies are inherited in an autosomal recessive manner, while creatine transporter disorders are X-linked. 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 guanidine acetic 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 have seizures.
Creatine deficiency syndromes are diagnosed by measuring guanidine acetic 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 guanidine acetic acid, and low creatinine.
- Patients with AGAT deficiency usually show normal to low creatine, low guanidine acetic acid, and normal to low creatinine.
- Patients with SLC6A8 deficiency show increased creatinine, normal guanidine acetic 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 a deficiency in the creatine transporter, whereas girls with a creatine transporter mutation benefit from creatine intake.
See also: Creatine Metabolism, Blood, Creatine, Plasma and, Creatine, Urine
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