## **Core Concept**
The question combines features of congenital cyanotic heart disease and polydactyly, suggesting a genetic syndrome that affects both limb development and cardiac morphogenesis. Congenital cyanotic heart diseases are characterized by conditions that lead to cyanosis due to right-to-left shunting of blood or obstruction to pulmonary blood flow. Polydactyly, an extra digit, is a form of limb abnormality.

## **Why the Correct Answer is Right**
The correct answer, **C. Ellis-van Creveld syndrome**, is a rare genetic disorder characterized by short-limbed dwarfism, polydactyly, and ectodermal dysplasia, often associated with congenital heart defects, particularly cyanotic heart diseases like single atrium or single ventricle. This syndrome is caused by mutations in the EVC1 or EVC2 genes. The combination of polydactyly and congenital cyanotic heart disease makes Ellis-van Creveld syndrome a likely diagnosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While certain syndromes like **A. Down syndrome** can have cardiac anomalies, they are not typically cyanotic heart diseases and are not characteristically associated with polydactyly.
- **Option B:** **B. Turner syndrome** primarily affects females and is associated with bicuspid aortic valve and coarctation of the aorta, not typically cyanotic heart disease or polydactyly.
- **Option D:** **D. Marfan syndrome** is known for tall stature, arachnodactyly (long fingers), and cardiac issues like aortic root dilatation and mitral valve prolapse, not polydactyly or cyanotic congenital heart disease.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Ellis-van Creveld syndrome is one of the ciliopathies, a group of disorders caused by defects in the structure or function of cilia. This syndrome often presents with a distinctive combination of skeletal, ectodermal, and cardiac abnormalities. Recognizing the association between polydactyly and specific congenital heart defects can help in diagnosing these syndromes.

## **Correct Answer: C. Ellis-van Creveld syndrome**