The MN test is for blood groups MM, MN, NN. This is used in the book Live Right 4 Your Type to further refine your diet, and in the SWAMI software.
Research suggests that people with the NN blood group may get more benefit from LDL cholesterol reduction with a low fat diet and have a lower incidence of bipolar depression, and women with this blood group may live longer.
The MM blood group antigen is the precursor for the Thomsen-Friedenreich (T) antigen, which is expressed on certain cancer cells.
More information about the MN blood group, diet and disease is available in the Complete Blood Type Encyclopedia by Dr. Peter D'Adamo.
Reference: Eat Right for Your Type Complete Blood Type Encyclopedia by Peter J D'Adamo. Pub. G P Putnam's Sons; 1st Riverhead Books (1 Jan. 2002), 576 pages. ISBN: 1573229202.