Which condition produces short-limb dwarfism with proximal segments more involved than distal?

• A. Arthrogryposis multiplex congenita
• B. Fibrodysplasia ossificans progressiva
• C. Spondylocostal dysostosis
• D. Achondroplasia

Answer: (D)

Proximal limb shortening with relatively normal hands and feet—rhizomelic dwarfism—is the hallmark pattern here. Achondroplasia is driven by a gain-of-function mutation in FGFR3 that chronically inhibits chondrocyte proliferation in growth plates, especially affecting endochondral ossification of the long bones. This leads to disproportionately shortened proximal segments (humerus, femur) while the distal parts are less affected. Clinically, you’d also see macrocephaly with frontal bossing and midface hypoplasia, which helps distinguish it from other skeletal disorders. The other conditions involve contractures, heterotopic ossification, or spinal/rib defects and do not produce the characteristic rhizomelic pattern of limb shortening seen with achondroplasia.