NGLY1 and Osteopenia: Given the reports on potential para-autocrine functions of mammalian Dpp homologs (Grimsrud et al., 1999; Rege et al., 2015; Shukunami et al., 2000; Tokola et al., 2015) and prominent human pathologies associated with dysregulated BMP signaling in ophthalmic, gastrointestinal and musculoskeletal systems (Wang et al., 2014), tissue-specific alterations in BMP signaling might contribute to some of the NGLY1 deficiency phenotypes including retinal abnormalities, delayed bone age and osteopenia, small feet and hands, and chronic constipation (Enns et al., 2014; Lam et al., 2017).