**Core Concept:** Achondroplasia is a type of dwarfism caused by a mutation in the FGFR3 gene, which leads to abnormal bone growth and short stature. Dwarfism can manifest with various physical features, including disproportionate limb-to-body growth, prominent forehead, and retruded maxilla.

**Why the Correct Answer is Right:** Achondroplasia is the most common form of autosomal dominant dwarfism, accounting for about 60% of cases. The mutation in the FGFR3 gene results in increased bone growth inhibition, leading to short stature and disproportionate limb-to-body growth. The prominent forehead is caused by the enlarged frontal sinuses and the retruded maxilla is due to the shortened maxillary bone and delayed eruption of teeth.

**Why Each Wrong Option is Incorrect:**

A. Hypophosphatasia: This is a rare autosomal recessive disorder affecting bone mineralization, resulting in low bone mineral density and weak bones. It does not cause disproportionate limb-to-body growth or prominent forehead.

B. Hypothyroidism: Although hypothyroidism can cause short stature, it does not typically result in disproportionate limb-to-body growth or prominent forehead.

C. Acromegaly: This is a hormonal disorder caused by overproduction of growth hormone, leading to disproportionate limb-to-body growth but typically not retruded maxilla.

D. Diabetes mellitus: Diabetes does not cause the physical features mentioned in this question.

**Clinical Pearl:** Achondroplasia is a clinical diagnosis based on the patient's presentation of short stature, disproportionate limb-to-body growth, and characteristic facial features. This diagnosis helps guide further investigations and management for the patient.