GSS and cerebellar ataxia: Their key clinical features included the following: relatively well-compensated anemia, progressive spinocerebellar degeneration, extremely low erythrocyte glutathione (less than 5% of normal), severely reduced GCS activity (2–7% of normal), normal glutathione synthetase (GS) activity, learning disabilities with dyslexia, severe progressive ataxia with myopathy, and psychotic episodes (possibly triggered by sulfamethoxazole–trimethoprim).