The fairly mild osteopenia observed under baseline conditions in SOST Tg mice (see Fig. 1A, B) is in line with the moderate overexpression of SOST under control of the human SOST promoter and distant cis-regulatory elements present in the BAC transgene reaching expression levels within the physiologic range(28) (see Fig. 1C, D). The gene discussed is SOST; the disease is Osteopenia.