Identify the genetic condition from the image shown below
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Key features of Achondroplasia include disproportionate short stature (rhizomelic shortening - proximal limbs), macrocephaly with frontal bossing, midface hypoplasia, and lumbar lordosis.
It exclusively affects endochondral ossification, meaning intramembranous ossification (which forms the cranial vault and facial bones) remains normal, explaining the large head relative to the body.
Concept:
The question asks to identify a genetic skeletal dysplasia based on a provided clinical image of a hand.
The image (as described by the clinical key) demonstrates a "trident hand" deformity.
We must correlate this specific clinical sign with the correct skeletal dysplasia syndrome. Explanation: • Achondroplasia is the most common form of short-limb dwarfism.
• It is inherited in an autosomal dominant manner, although approximately 80% of cases are due to de novo spontaneous mutations.
• The underlying genetic defect is a gain-of-function mutation in the FGFR3 (Fibroblast Growth Factor Receptor 3) gene, which inappropriately inhibits chondrocyte proliferation at the growth plate, severely affecting endochondral ossification.
• A classic clinical feature of achondroplasia in the extremities is the "trident hand".
• The trident hand appearance occurs because the fingers are short and stubby (brachydactyly), and there is an increased space (divergence) between the middle and ring fingers (the third and fourth digits).
• This specific divergence gives the hand a three-pronged or trident-like appearance.
• Thanatophoric dysplasia is also caused by FGFR3 mutations but is a severe, usually perinatal lethal form of skeletal dysplasia characterized by extremely short limbs, narrow thorax, and cloverleaf skull, lacking the classic presentation of a living patient with a simple trident hand.
• Hypochondroplasia is a milder form of achondroplasia but typically does not feature the prominent trident hand or severe craniofacial abnormalities seen in classic achondroplasia.
• Osteogenesis imperfecta is a disorder of type I collagen characterized by brittle bones, frequent fractures, and blue sclerae, but it does not cause the trident hand deformity. Final answer:
The condition shown is Achondroplasia, classically characterized by the trident hand deformity.
