X-gebonden mentale retardatie door creatine transporter defect

Two boys, aged 4 and 8 years, consulted a pediatrician for psychomotor and severe language/speech delay. Both patients showed growth deficiency and a gracile muscular system. Further investigation revealed an increased urinary creatine/creatinine ratio. DNA sequence analysis of SLC6A8 on the X-chromosome revealed two different mutations resulting in creatine transporter defect. Creatine transporter defect is a recently described cause of X-linked mental retardation that appears to be relatively frequent. The disease is characterized by the neuropsychological profile with mental retardation, ADHD, semantic-pragmatic language disorder and oral dyspraxia. The diagnosis is based on a combination of at least two tests: assessment of the urinary creatine/creatinine ratio, ¹H-MRS of the brain, DNA sequence analysis of SLC6A8 or creatine uptake assay in cultured fibroblasts. Every male patient with mental retardation, speech/language disorder and/or growth deficiency should be screened for creatine transporter defect.