**Core Concept**
Holt-Oram syndrome is a genetic disorder affecting the upper limbs and heart, characterized by abnormalities in the upper limb (hand and arm) and congenital heart defects. It is a form of autosomal dominant inheritance, caused by mutations in the TBX5 gene.

**Why the Correct Answer is Right**
Holt-Oram syndrome is associated with abnormalities in the limbs, such as radial club hand, and congenital heart defects, including atrial septal defects, ventricular septal defects, and tetralogy of Fallot. The TBX5 gene is a transcription factor that plays a crucial role in the development of the upper limbs and heart. Mutations in this gene disrupt normal limb and heart development, leading to the characteristic features of Holt-Oram syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a characteristic feature of Holt-Oram syndrome. While some individuals with Holt-Oram syndrome may have skeletal abnormalities, polydactyly is not a specific feature of this condition.
**Option B:** While Holt-Oram syndrome can be associated with cardiac abnormalities, Marfan syndrome is a separate genetic disorder that primarily affects the cardiovascular system and is caused by mutations in the FBN1 gene.
**Option C:** This option is not a characteristic feature of Holt-Oram syndrome. While some individuals with Holt-Oram syndrome may have limb abnormalities, camptodactyly is not a specific feature of this condition.

**Clinical Pearl / High-Yield Fact**
Holt-Oram syndrome is a classic example of a genetic disorder that affects both the upper limbs and heart, highlighting the importance of considering both limb and cardiac abnormalities in the diagnosis of genetic disorders.

**Correct Answer:** A. Radial club hand