The NM_005629.4:c.1146_1150dup (p.Leu384ArgfsTer14) (a.k.a. NC_000023.11:g.153693909_153693913dup) in SLC6A8 is a frameshift variant predicted to cause a premature stop codon in biologically-relevant-exon 8 of 13, leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1). A male patient with clinical features consistent with creatine transporter deficiency, hemizygous for the variant, was reported to have had elevated urine creatine levels on two occasions (PMID: 27096572) (PP4). His mother did not appear to carry the variant; maternity was not confirmed (PM6). The variant is absent in gnomAD v2.1.1. (PM2_Supporting). In summary, this variant meets the criteria to be classified as pathogenic for creatine transporter deficiency. SLC6A8-specific ACMG/AMP criteria applied, as specified by the ClinGen CCDS Variant Curation Expert Panel (Specifications Version 1.1.0): PVS1, PM6, PP4, PM2_Supporting. (Classification approved by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel on August 8, 2023).