Impressions Scale score of 3 or less, reflecting only mild symptoms, were declared responders, whereas other subjects were deemed non-responders. Li responders were then followed on Li monotherapy for up to 2 years. The responders remained stable for an average of 23 months on Li monotherapy, whereas the non-responders failed to remit from their index episode after an average trial of Li of 3 months. All subjects were white males. The characteristics of these subjects are detailed in Supplementary Table 4. Four-millimetre punch skin biopsies were obtained under sterile conditions from a few centimetres below the iliac crest.
