High frequency of creatine deficiency syndromes in patients with unexplained mental retardation

Cerebral creatine deficiency syndromes (CCDSs) are inborn errors of metabolism that include two autosomal recessive creatine biosynthesis defects (arginine–glycine amidinotransferase [AGAT; OMIM 602360] and guanidinoacetate methyl transferase [GAMT; OMIM 601240] deficiency) and an X-linked creatine transporter defect (OMIM 300036).¹ The clinical phenotype is variable, associating nonspecific mental retardation, epilepsy, extrapyramidal movement disorders, and autistic behavior. The frequency of CCDS is unknown and probably underestimated. We report a high frequency of CCDS in mentally retarded children, mostly boys with an X-linked creatine transporter deficiency.

Methods.

Over a period of18 months, children referred to the Department of Pediatric Neurology with unexplained mild to severe mental retardation, normal karyotype, and absence of fragile X syndrome were prospectively screened for CCDS. Children were from diverse ethnic backgrounds. Children with polymalformative syndromes were excluded. Creatinine metabolism was evaluated using creatine/creatinine and guanidinoacetate (GAA)/creatinine ratios on a spot urine.² Diagnosis was further confirmed using brain proton MR spectroscopy (H-MRS) and …