**Core Concept**
Restrictive cardiomyopathy is a type of cardiomyopathy characterized by the stiffening of the heart muscle, which impairs the heart's ability to relax and fill with blood. This condition leads to diastolic dysfunction, where the ventricles cannot accommodate the normal volume of blood during diastole. The stiffened heart muscle can be due to various causes, including genetic mutations, amyloidosis, and sarcoidosis.

**Why the Correct Answer is Right**
The correct answer involves the association of restrictive cardiomyopathy with systemic diseases. One of the classic causes of restrictive cardiomyopathy is amyloidosis, where abnormal proteins called amyloid fibrils accumulate in the heart muscle, leading to stiffness and diastolic dysfunction. Another cause is sarcoidosis, an inflammatory disease that can infiltrate the heart muscle and lead to fibrosis and stiffness. In some cases, restrictive cardiomyopathy can also be caused by genetic mutations, such as those affecting the troponin or desmin genes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the causes of restrictive cardiomyopathy.
**Option B:** This option may be related to other types of cardiomyopathy, but not restrictive cardiomyopathy specifically.
**Option C:** While amyloidosis is a correct cause of restrictive cardiomyopathy, this option is too vague and does not specify the correct disease.

**Clinical Pearl / High-Yield Fact**
One key point to remember is that restrictive cardiomyopathy can be caused by a variety of systemic diseases, making a thorough history and physical examination crucial in making the diagnosis.

**Correct Answer:** D. Amyloidosis