Which type of osteogenesis imperfecta is the most lethal, with bone shortening and a bell-shaped chest?

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Answer: (B)

Osteogenesis imperfecta shows a range of severity, and the most lethal form is the perinatal lethal type. In this form, bones are extremely fragile and fractures occur in utero or at birth, leading to marked bone shortening and deformity. The chest becomes small and bell-shaped because the rib cage is severely constricted, which impairs lung development (pulmonary hypoplasia) and causes death soon after birth. Other forms are less severe: Type I is mild with fractures after birth and normal lifespan; Type III is severe with deformities but individuals can survive beyond the neonatal period; Type IV is moderately severe. The combination of eye-opening in utero fractures, significant shortening, and a bell-shaped chest is classic for the perinatal lethal form.