Presence of normal creatine in the muscle of a patient with a mutation in the creatine transporter: a case study
To date, more than seven families have been reported who carry a mutation in the X-linked creatine-transporter (CrT) gene. The resulting lack of creatine in the brain is associated with mental retardation, severe expressive language disorder, mild epilepsy, and a complete absence of Cr in the brain (measured using MRS). Conversely, these patients had no observable cardiac or musculo-skeletal deficits. In this case study, a 22-year-old patient underwent surgical repair for scoliosis. Proton MRS of this patient's brain demonstrated the near-absence of creatine and phosphocreatine within the cerebral white and deep gray matter structures. Cerebral atrophy was noted with serial MRI examinations. Subsequent genetic and metabolic analysis showed some biochemical anomalies consistent with a CrT deficiency. The mutation in this patient was identified as a deletion at phenylalanine 107 (delF107). Control muscle biopsies were obtained from archived samples, which had been taken with informed consent during routine muscle biopsies for diagnostic purposes. We determined that the total Cr concentration in the skeletal muscle biopsy was 39.3 +/- 2.94 mmol/kg wet wt., which is not significantly different from non-CrT controls, n = 3 (43.3 +/- 3.57 mmol/kg wet wt.). We conclude that the brain appears to lack the ability to transport creatine when there is a mutation in the CrT gene. However, the muscle utilizes another mechanism for maintaining normal creatine levels. Identifying this alternative creatine-transport mechanism may be useful in treating the neurologic and cognitive impairments of patients with creatine-transporter deficiency.