The NM_005629.4:c.92C>T variant in SLC6A8 is a missense variant predicted to cause the substitution of a proline by a methionine at amino acid position 31 (p.Pro31Leu). This variant has been previously reported in one individual with seizures, neurological regression, and spasticity (PMID: 31222513), who was found by exome sequencing to be hemizygous for the variant; however, biochemical studies were not reported for this individual, such that neither PP4 nor PS4 apply. In gnomAD v2.1.1, the highest population minor allele frequency is 0.00013 (4/30763 alleles, 1 hemizygote), which is greater than the ClinGen CCDS VCEP’s threshold for PM2_Supporting (<0.00002) but less than the ClinGen CCDS VCEP’s threshold for BS1 (>0.0002), such that neither of these criteria are met. The computational predictor REVEL gives a score of 0.114 (BP4). There is a ClinVar entry for this variant (Variation ID:572616). In summary, this variant meets the criteria to be classified as a variant of uncertain significance for creatine transporter deficiency. SLC6A8-specific ACMG-AMP criteria applied, as specified by the ClinGen CCDS VCEP (Specifications Version 1.1.0): BP4. (Classification approved by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel on November 8, 2024)