Absent lateral 1/3rd of clavicle is seen in –
**Core Concept**
The **cleidocranial dysplasia** is a rare genetic disorder that affects the development of bones and teeth. This condition is characterized by the abnormal development of the clavicles, which can lead to their partial or complete absence. The **clavicle** plays a crucial role in the formation of the shoulder girdle and serves as an attachment point for several muscles.
**Why the Correct Answer is Right**
The correct answer is related to **cleidocranial dysplasia**, a condition where the lateral 1/3rd of the **clavicle** is often absent. This is due to the impaired development of the **clavicle** during embryogenesis, resulting in its partial or complete absence. The **mutation** in the RUNX2 gene is responsible for this condition.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not associated with the absence of the lateral 1/3rd of the clavicle.
**Option B:** This option is incorrect as it is not related to **cleidocranial dysplasia**.
**Option C:** This option is incorrect because it does not describe the characteristic features of **cleidocranial dysplasia**.
**Clinical Pearl / High-Yield Fact**
The absence of the lateral 1/3rd of the **clavicle** is a characteristic feature of **cleidocranial dysplasia**. This condition can also be associated with other skeletal abnormalities, such as delayed closure of the fontanelles and supernumerary teeth.
**Correct Answer:** C. Cleidocranial dysplasia.