DLK1 and osteoporosis: We and others have shown that the increased serum levels of FA1 was associated with human pathological conditions including neurofibromatosis (5 times higher than the normal range) (Jensen et al., 1999), renal failure (10 times higher) (Jensen et al., 1997), small cell lung cancer patients (10–1000 times higher) (Harken et al., 1999), and estrogen deficiency-induced osteoporosis in post-menopausal women (Abdallah et al., 2011a).