Which autosomal dominant disorder is the most common form of dwarfism?

• A. Achondroplasia
• B. Red-green color blindness
• C. Lactose tolerance
• D. Fragile X syndrome

Answer: (A)

Achondroplasia shows how a single dominant mutation can cause disproportionate short stature. The condition comes from a gain-of-function mutation in FGFR3, which slows the growth of long bones by inhibiting chondrocyte activity in the growth plates. That leads to short limbs with a relatively normal torso, a prominent forehead, and midface hypoplasia—the classic dwarfism phenotype. Most cases arise from new mutations rather than inheritance from a parent, and having two dominant copies is usually lethal in infancy, so affected individuals are typically heterozygotes. The other options don’t fit because red-green color blindness is X-linked, lactose tolerance is not a disease causing dwarfism, and Fragile X syndrome is X-linked and primarily affects cognitive development rather than stature.