**Core Concept**
Anorexia Nervosa is a complex eating disorder characterized by a distorted body image, excessive weight loss, and restrictive eating habits. It is a serious psychiatric condition with significant physical and psychological consequences.

**Why the Correct Answer is Right**
Amenorrhea, or the absence of menstruation, is a common feature of Anorexia Nervosa due to the significant weight loss and hormonal imbalances that occur as a result of the disorder. The hypothalamic-pituitary-gonadal axis is disrupted, leading to decreased estrogen production and subsequent amenorrhea. In fact, amenorrhea is one of the diagnostic criteria for Anorexia Nervosa, and its presence is often used as a marker for the severity of the disorder.

**Why Each Wrong Option is Incorrect**
**Option A:** Predominantly seen in females - This statement is true, as Anorexia Nervosa is more common in females, with a female-to-male ratio of approximately 10:1. However, this is not the correct answer as it is not an exception to the features of Anorexia Nervosa.
**Option B:** BMI index is higher than normal Population - This statement is false, as individuals with Anorexia Nervosa typically have a low BMI index, often below 17.5. This is a key diagnostic feature of the disorder.
**Option D:** Malabsorption Syndrome is most common cause - This statement is false, as malabsorption syndrome is not a common cause of Anorexia Nervosa. The disorder is primarily characterized by restrictive eating habits and excessive weight loss, rather than malabsorption.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Anorexia Nervosa has a high mortality rate, with a mortality rate of 5.86% per decade, making it one of the most deadly psychiatric disorders. Early recognition and treatment are crucial to improve outcomes.

**✓ Correct Answer: C. Amenorrhea is rare**