A 2½ year old child with severe horizontal bone resorption and normal cementum is suffering from?
**Core Concept**
The question is testing the understanding of a rare genetic disorder characterized by severe horizontal bone loss, primarily affecting the permanent teeth. This condition is caused by an abnormality in the production of a crucial protein involved in tooth development.
**Why the Correct Answer is Right**
The child is suffering from **Rieger anomaly**, a rare congenital disorder that affects the development of teeth and bones. The condition is characterized by severe horizontal bone resorption, which leads to the loss of permanent teeth. The presence of normal cementum in the child suggests that the disorder is not affecting the cementum-producing cells, which is a key diagnostic feature. The underlying cause of Rieger anomaly is a mutation in the _PITX2_ gene, which codes for a transcription factor essential for tooth development.
**Why Each Wrong Option is Incorrect**
**Option A:** **Amelogenesis imperfecta** is a condition characterized by abnormalities in the enamel of teeth, which is not related to horizontal bone resorption.
**Option B:** **Hypophosphatasia** is a genetic disorder affecting bone mineralization, but it does not specifically cause horizontal bone resorption.
**Option C:** **Gingivitis** is an inflammatory condition of the gums, which is not related to the severe bone loss seen in Rieger anomaly.
**Clinical Pearl / High-Yield Fact**
Rieger anomaly is a rare condition that can be distinguished from other dental disorders by the presence of normal cementum and severe horizontal bone resorption. It is essential to recognize this condition early to prevent tooth loss and ensure proper dental care.
**Correct Answer:** D.