All are true about Achondroplasia except
**Core Concept**
Achondroplasia is the most common form of short-limbed dwarfism, characterized by a mutation in the FGFR3 gene. This mutation leads to impaired chondrocyte proliferation and differentiation, resulting in short stature and characteristic skeletal features.
**Why the Correct Answer is Right**
Achondroplasia is an autosomal dominant disorder, meaning a single copy of the mutated gene is sufficient to cause the condition. The mutation affects the fibroblast growth factor receptor 3 (FGFR3) gene, which plays a crucial role in regulating chondrocyte growth and development. The resulting impairment in chondrocyte proliferation and differentiation leads to the characteristic skeletal features of achondroplasia, including short limbs, macrocephaly, and a distinctive "bee-stung" nose.
**Why Each Wrong Option is Incorrect**
**Option A:** Achondroplasia is not caused by a deficiency of growth hormone (GH). While GH is essential for growth and development, achondroplasia is a result of a specific genetic mutation affecting the FGFR3 gene.
**Option B:** Achondroplasia is not characterized by a normal growth velocity during childhood. In fact, children with achondroplasia often experience delayed growth and development, particularly in the first few years of life.
**Option C:** Achondroplasia is not typically associated with a normal life expectancy. While individuals with achondroplasia can live into adulthood, they may experience a range of complications, including spinal stenosis, hydrocephalus, and sleep apnea.
**Clinical Pearl / High-Yield Fact**
Achondroplasia is the most common form of short-limbed dwarfism, accounting for approximately 70% of all cases. It is essential for clinicians to recognize the characteristic skeletal features and genetic mutation associated with this condition to provide appropriate management and support.
**Correct Answer: D.**