SLC6A8 and hyperinsulinemic hypoglycemia, familial, 4: Finally, keeping in mind that guanidinoacetic acid is capable of increasing brain creatine in normal subjects [14], we hypothesized that it may be used to increase creatine content in patients affected by creatine transporter deficiency, a rare disease in which the creatine transporter is malfunctioning, preventing creatine uptake and synthesis by the brain [15].