This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolic Disorders of Bone, Subject name: Orthopaedics
A 9-year-old child with high arched palate has shoulders meeting in front of his chest. He has: 
Select and explain. 
A. Erb's palsy, B. Cleidocranial dysostosis, C. Chondro-osteodystrophy, D. Coical hyperostosis
B: Cleidocranial dysostosis
Answer: B: Cleidocranial dysostosis 
Explanation: CLEIDOCRANIAL DYSOSTOSIS-AD Clinical and Radiological Features: Skull Involvement- Elfin faces- skull is wider but the face appears small and flat looking (hypoplastic bones) Eyes are wide set Deciduous teeth erupt normally,permanent teeth are delayed and maldeveloped. Clavicles maybe underdeveloped or absent. M/C defect is loss of lateral 1/3rd > loss of middle third of clavicle Bilateral clavicle hypoplasia, child can touch the shoulders together in front of the chest. Limbs- Coxa vara is seen, 2nd metacarpal is usually long