Treatment and Improved Outcomes of Three Adult Patients With Guanidinoacetate Methyltransferase (<scp>GAMT</scp>) Deficiency

Guanidinoacetate methyltransferase (GAMT) deficiency is a creatine synthesis disorder caused by biallelic pathogenic variants in <i>GAMT</i>. Early diagnosis and treatment can lead to normal neurocognitive outcomes, which has prompted its recent addition to the Recommended Uniform Screening Panel. Treatment typically includes creatine and ornithine supplementation, with or without arginine restriction or sodium benzoate. Here, we present the clinical outcomes of 3 adult patients with GAMT deficiency who began creatine and ornithine supplementation at varying ages. One patient started on treatment at 14 months of age and has had near-normal neurocognitive outcomes, highlighting the positive clinical impact of early treatment. Our findings also emphasize the need to continue treatment throughout adulthood, but further research is required to understand the natural history and determine the optimal treatment of GAMT deficiency in adults.