Are plasma homocysteine and methionine elevated when binging and purging behavior complicates anorexia nervosa? Evidence against the transdiagnostic theory of eating disorders.

OBJECTIVE: To determine whether plasma total homocysteine (tHcy) and plasma methionine levels are different in anorexia nervosa restricting type (AN-R) compared to anorexia nervosa binge eating/purging type (AN-BP).
METHODS: Cross-sectional design.
SUBJECTS: Subjects were recruited from the outpatient program of the Eating Disorders Program at St. Paul's Hospital, Vancouver, Canada. All subjects had a current Diagnostic and Statistical Manual of mental Disorders - Fourth Edition (DSM-IV) AN-R, or AN-BP diagnosis. Controls were recruited from staff and trainees of Child and Family Research Institute, and Children's and Women's Hospital, University of British Columbia.
RESULTS: Samples were obtained from AN-R (N=30), AN-BP (N=32) and control women (N=73) and men (N=33). The 5- 95th% confidence intervals from the control women were taken as the normal range. The plasma tHcy and methionine for the control group had a 5-95th percentile range of 5.66-10.57 and 15.3-40.2 microM, respectively. Plasma tHcy was elevated in women with AN-BP (9.24+/-0.85 microM, N=32) but not with AN-R (7.90+/-0.38 microM, N=30). Plasma methionine was decreased in women with AN-BP (22.2+/-1.43 microM, N=32) compared to the control group of women (25.1+/-0.89 microM). The plasma methionine/tHcy ratio was elevated in the women with AN-BP (0.50+/-0.09) but not in those with AN-R (0.34+/-0.03).
CONCLUSION: Elevated plasma tHcy and decreased plasma methionine are consistent with impaired homocysteine remethylation. Altered methyl transfer capacity or methyl deficiency could impair monoamine neurotransmitter metabolism potentially impacting cognitive and psychological function.We hypothesize that the treatment of AN-BP should consider the need for nutritional support of methyl metabolism.