Guanidinoacetate methyltransferase deficiency

Guanidinoacetate methyltransferase deficiency (GAMT deficiency) is an autosomal recessive cerebral creatine deficiency that primarily affects the nervous system and muscles. It is the first described disorder of creatine metabolism, and results from deficient activity of guanidinoacetate methyltransferase, an enzyme involved in the synthesis of creatine. Clinically, affected individuals most commonly present with developmental delay, behavior disorder, and seizures. Diagnosis can be suspected on clinical findings, and confirmed by specific biochemical tests, brain magnetic resonance spectroscopy, or genetic testing. Biallelic pathogenic variants in the GAMT gene are the underlying cause of the disorder. After GAMT deficiency is diagnosed, it can be treated by dietary adjustments, including supplementation with creatine. Treatment is highly effective if started early in life. If treatment is started late, it cannot reverse brain damage which has already taken place. The prevalence of GAMT deficiency is estimated to be 1:250,000.