**Core Concept**
Early epiphyseal closure is a condition where the growth plates in bones fuse prematurely, leading to short stature and potential long-term musculoskeletal consequences. This phenomenon is influenced by various endocrine, nutritional, and genetic factors.

**Why the Correct Answer is Right**
The correct answer is linked to growth hormone (GH) deficiency, which affects the epiphyseal growth plates. GH stimulates the production of insulin-like growth factor 1 (IGF-1), which in turn promotes chondrocyte proliferation and hypertrophy in the growth plates. A deficiency in GH leads to decreased IGF-1 levels and subsequent epiphyseal closure. This is often seen in patients with pituitary disorders, such as hypopituitarism.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypothyroidism is associated with delayed epiphyseal closure, not early closure.
**Option B:** Cushing's syndrome is characterized by excessive glucocorticoid levels, which can lead to growth suppression and delayed epiphyseal closure, but not early closure.
**Option C:** Turner syndrome is a genetic disorder that affects females and is characterized by short stature due to ovarian dysgenesis and hormonal imbalances, but it is not directly associated with early epiphyseal closure.

**Clinical Pearl / High-Yield Fact**
It is essential to distinguish between early and delayed epiphyseal closure, as the underlying causes and consequences can be vastly different. Remember that GH deficiency is a key factor in early epiphyseal closure, and patients with this condition may require GH replacement therapy.

**Correct Answer:** C. Turner syndrome.