PAEP and hematocrit: The first linkage study in AITD consisted of 56 multiplex Caucasian family members (families with either GD or HT as well as unaffected members) and identified linkage at 7 regions, 3 were GD specific termed, GD-1 (14q31) (GD-1 locus displayed in Fig. 2A), GD-2 (20q11.2), GD-3 (Xp21), 2 in HT called HT-1 (13q32) and HT-2 (12q22) and one common AITD locus, AITD-1 (6p11) [16].