**Core Concept:** Polygenic disorders are conditions caused by the interaction of multiple genes, while monogenic disorders are due to a single gene mutation.

**Why the Correct Answer is Right:** Osteoporosis is a polygenic disorder, meaning it is influenced by multiple genes interacting together. Although environmental factors also contribute, the primary cause lies in the genetic makeup of an individual.

**Why Each Wrong Option is Incorrect:**

A. Monogenic Disorders (Option D) involve a single gene mutation, which is not the case for osteoporosis.
B. Mitochondrial Disorders (Option C) are caused by mutations in mitochondrial DNA, which is separate from the nuclear genes involved in osteoporosis.
C. Nutritional Deficiencies (Option B) are typically caused by single dietary factors, unlike osteoporosis, which is a consequence of multiple gene interactions.

**Clinical Pearl / High-Yield Fact:** Osteoporosis is often referred to as the "quiet thief of bones" because it progresses slowly without noticeable symptoms until a fracture occurs.

**Correct Answer:** Monogenic Disorders (Option D) are not polygenic disorders, and osteoporosis is an example of a polygenic disorder.