The NM_005629.4:c.262+1G>T variant occurs within the canonical splice donor of intron 1/12 (exon 1/13) of SLC6A8. It is predicted to cause skipping of biologically-relevant-exon 1/13, resulting in a frameshift leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1). This variant is absent from gnomAD v2.1.1, therefore PM2_Supporting criteria is applicable. In silico algorithm SpliceAI predicts a donor loss -1bp from this position (delta score=0.99). This variant has not been previously reported in ClinVar. The c.262+1G>T variant in SLC6A8 has been reported in one individual, a male diagnosed at 1.8y of age (patient 6) with moderate intellectual disability, seizures, autistic features, aggressive and self injurious behaviors. This individual had a urine creatine to creatinine ratio of 14,874 (normal = 6–1200 μmol/mmol creatinine) and a H-MRS showing reduced creatine peak [PMID: 29435807], therefore this reported individual meets criteria for PP4_Strong. In summary, this variant meets the criteria to be classified as Pathogenic for Creatine Transporter Deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel (Specifications Version 1.0): PVS1, PP4_Strong, PM2_Supporting. (Classification approved by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel on March 29, 2024)