Can brittle bone disease be fatal?

Yes it could be: Some new born die during delivery because they have so many fractures during delivery. (osteogenesis imperfecta).

Yes: There are several different genetic forms of this disorder. The most severe are born with respiratory insufficiency due to multiple rib fractures and inability to develop good lung volume.They also have multiple bone fractures with simple movement, or due to delivery forces.Those that survive birth often die in the first months from complications.