Cerebral creatine deficiency syndrome with a novel missense variant in SLC6A8 gene

Cerebral creatine deficiency syndromes (CCDS) are three metabolic diseases characterized by loss of function in three proteins (GATM, GAMT, and SLC6A8) that required in creatine (Cr) synthesis pathway and transport. In this study, we aimed to identify the causal variant in a male who was 12-year-old manifesting intellectual disability (ID), seizures, expressive dysphasia and autism-like behavior. Urinary Cr metabolite measurements and MRI-spectroscopy (MRS) findings were consistent with CCDS. Molecular analysis revealed de novo hemizygous SLC6A8 (NM_005629.4): c.1400 T > G (p.Met467Arg) variant. The variant was not found in ClinVar, (the date of access: April 23th, 2023) and population databases (ExAC, gnomAD, 1000 Genomes, ESP 6500, Turkish Variome, GenomeAsia, Iranome, GME Variome, TOPMed Bravo and 4.7KJPN), it alters the physicochemical properties of the amino acid, the region is moderately conserved across species and in-silico prediction tools (REVEL, CADD, SIFT, PolyPhen2, Mutation Taster, MetaLR, MCAP, MetaRNN and MutPred) unanimously emphasize pathogenicity. Based on this evidence, the variant was interpreted as "likely pathogenic" according to the ACMG criteria (PS2, PM2,PP3, and PP4-S). This report may further elucidate the nature and phenotypic consequences of SLC6A8 variants.