NF1 and Osteopenia: As neurofibromin 1 (NF1) functions as a negative regulator of the ERK MAPK pathway, loss of function mutations in NF1 cause neurofibromatosis type 1 (NF1) syndrome, characterized by a complex set of bone phenotypes that can include osteopenia and impaired fracture healing as well as cutaneous neurofibromas (Bok et al., 2020; Crawford and Schorry, 1999; de la Croix Ndong et al., 2014).