The current era of drug development has evolved significantly. Patient advocacy organizations are moving beyond simply supporting community members and are taking the reins to improve the speed of diagnoses, initiate therapeutic discoveries, and lay the groundwork to ensure successful clinical trials. The Association for Creatine Deficiencies (ACD) is an international parent-led patient advocacy organization focused on the three ultra-rare neurodevelopmental monogenic disorders resulting in Cerebral Creatine Deficiency Syndromes (CCDS). These include X-linked creatine transporter deficiency (CTD), guanidinoacetate methyltransferase (GAMT) deficiency, and l-arginine:glycine amidinotransferase (AGAT) deficiency. While each is rare in its own right, the unified CCDS community is effectively advancing the field of CCDS with each disorder benefiting from progress made in the other two disease areas. ACD collaborators include caregivers, academic researchers, clinicians, industry partners, and policymakers. Since its founding in 2012, the organization has evolved and achieved significant milestones. These include advancements in disease diagnosis, investments in various therapeutic modalities, creation of a collaborative research community, a unified patient community contributing essential patient data, and repositories of patient-derived specimens. The initiatives of ACD are intended to create the earliest diagnosis possible through newborn screening, to have an effective treatment, and to make disease management strategies available to all members of the CCDS community, including those diagnosed at later stages and experiencing greater effects of the diseases.

L-arginine:glycine amidinotransferase (AGAT) deficiency is a rare autosomal recessive disorder affecting creatine biosynthesis, leading to developmental delay, intellectual disabilities, and myopathy. Unlike other creatine deficiency disorders, its link to epilepsy remains uncertain. This study presents the first reported epilepsy cases in AGAT deficiency, analyzing seizure patterns and response to creatine monohydrate supplementation. We retrospectively analyzed two AGAT-deficient probands identified through a national collaboration. Biochemical assessments of creatine and guanidinoacetate (GAA) levels in plasma and urine were performed using electrospray ionization tandem mass spectrometry and high-performance liquid chromatography methods. Brain magnetic resonance spectroscopy was conducted to evaluate cerebral creatine levels pre- and postsupplementation. Both probands carried the homozygous c.446G>A, p.(Trp149Ter) mutation in GATM, classified as pathogenic. The first, diagnosed at birth and treated with creatine from 4 months, had normal psychomotor development but developed focal epilepsy at 6 years, controlled with carbamazepine. The second, diagnosed at 5 years, presented with psychomotor delay, behavioral disturbances, and nocturnal seizures with unknown origin from age 4 years, later developing focal tonic seizures while awake. Initially the proband was unresponsive to carbamazepine; seizure control was achieved with valproate and lacosamide. Definitive conclusions on the role of creatine supplementation in epilepsy associated with AGAT deficiency cannot be drawn, as it was not modified after seizure onset in the first proband and introduced only after seizure control in the second. This study presents the first cases of epilepsy in AGAT deficiency, suggesting its prevalence may be underestimated. AGAT-related epilepsy appears to be part of the associated developmental encephalopathy, with focal seizures and minimal impact on psychomotor development. In AGAT deficiency, epilepsy is not linked to GAA accumulation as in other creatine deficiency disorders but rather to low brain creatine levels, which may affect γ-aminobutyric acidergic neurotransmission and seizure thresholds. The role of creatine supplementation in seizure control warrants further investigation.

Creatine is synthetized from arginine and glycine. There are two enzymes in the synthesis: l-arginine:glycine amidinotransferase and guanidinoacetate methyltransferase. After the synthesis, it is taken up by high-energy-requiring organs using creatine transporter. Biallelic pathogenic variants in GAMT result in guanidinoacetate methyltransferase deficiency and biallelic pathogenic variants in GATM result in l-arginine:glycine amidinotransferase deficiency. Hemizygous pathogenic variant in males and heterozygous pathogenic variant in females in SLC6A8 result in creatine transporter deficiency. Patients with these disorders present with a wide range of symptoms, including developmental delay, seizures, movement disorder, behavioral problems, and hypotonia. The diagnosis can be suspected by elevated guanidinoacetate and low creatine levels in body fluids in guanidinoacetate methyltransferase deficiency, low guanidinoacetate and low creatine levels in body fluids in l-arginine:glycine amidinotransferase deficiency, and elevated creatine-to-creatinine ratio in urine in creatine transporter deficiency in males as well as absent or significantly decreased creatine level in brain proton magnetic resonance spectroscopy. Genetic investigations such as targeted next-generation sequencing panel or exome sequencing can also identify these disorders; however, metabolite measurements and creatine in proton magnetic resonance spectroscopy are crucial to confirm the diagnosis. While all 3 disorders are currently treated with creatine supplementation, guanidinoacetate methyltransferase deficiency is also treated with ornithine supplementation and a protein- or arginine-restricted diet, and creatine transporter deficiency is treated with arginine and glycine supplementation (with no proven improvements).

l-arginine:glycine amidinotransferase (AGAT) and its metabolites homoarginine (hArg) and creatine have been linked to stroke pathology in both human and mouse studies. However, a comprehensive understanding of the underlying molecular mechanism is lacking. To investigate transcriptional changes in cerebral AGAT metabolism, we applied a transcriptome analysis in brains of wild-type (WT) mice compared to untreated AGAT-deficient (AGAT-/-) mice and AGAT-/- mice with creatine or hArg supplementation. We identified significantly regulated genes between AGAT-/- and WT mice in two independent cohorts of mice which can be linked to amino acid metabolism (Ivd, Lcmt2), creatine metabolism (Slc6a8), cerebral myelination (Bcas1) and neuronal excitability (Kcnip3). While Ivd and Kcnip3 showed regulation by hArg supplementation, Bcas1 and Slc6a8 were creatine dependent. Additional regulated genes such as Pla2g4e and Exd1 need further evaluation of their influence on cerebral function. Experimental stroke models showed a significant regulation of Bcas1 and Slc6a8. Together, these results reveal that AGAT deficiency, hArg and creatine regulate gene expression in the brain, which may be critical in stroke pathology.