**Core Concept**
Growth Hormone (GH) plays a crucial role in regulating growth, body composition, and metabolism. Its deficiency can lead to various clinical manifestations, including growth retardation, increased body fat, and decreased muscle mass.

**Why the Correct Answer is Right**
GH stimulates the production of Insulin-like Growth Factor-1 (IGF-1), which promotes growth and development. In GH deficiency, IGF-1 levels are decreased, leading to growth retardation, short stature, and delayed puberty. Additionally, GH regulates lipolysis, which is the breakdown of fat for energy. In GH deficiency, this process is impaired, resulting in increased body fat and decreased muscle mass.

**Why Each Wrong Option is Incorrect**
**Option A:**
GH deficiency is characterized by decreased IGF-1 levels, which affects growth and development. Therefore, growth retardation is a common feature of GH deficiency.

**Option B:**
While GH has anabolic effects, its deficiency leads to catabolic changes, including increased body fat and decreased muscle mass. Therefore, muscle wasting is not typically associated with GH deficiency.

**Option C:**
GH has a role in regulating glucose metabolism, but its deficiency is not directly associated with impaired glucose tolerance. Instead, GH deficiency is more likely to be associated with decreased lipolysis and increased body fat.

**Clinical Pearl / High-Yield Fact**
GH deficiency can be caused by various factors, including pituitary tumors, head trauma, and radiation therapy. It's essential to diagnose and treat GH deficiency early to prevent long-term growth and developmental issues.

**Correct Answer: A. Growth retardation**