**Core Concept**
Hyperkinetic disorder, also known as attention deficit hyperactivity disorder (ADHD), is characterized by excessive motor activity and inattention. It involves an imbalance in dopamine and norepinephrine neurotransmitter systems, affecting the prefrontal cortex and basal ganglia.

**Why the Correct Answer is Right**
The symptoms of hyperkinetic disorder include excessive motor activity, impulsivity, and inattention. The disorder is often associated with an imbalance in the dopamine and norepinephrine neurotransmitter systems, which affects the prefrontal cortex and basal ganglia. This imbalance is thought to be responsible for the characteristic symptoms of hyperkinetic disorder.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is a hallmark symptom of hyperkinetic disorder. Children with this condition often exhibit excessive motor activity, such as fidgeting or restlessness.

**Option B:** This option is also incorrect as impulsivity is a common symptom of hyperkinetic disorder. Children with this condition may have difficulty waiting their turn, interrupt others, or blurt out answers.

**Option C:** This option is incorrect as inattention is a primary symptom of hyperkinetic disorder. Children with this condition may have difficulty paying attention to details, following instructions, or completing tasks.

**Option D:** This option is correct as hyperkinetic disorder is not typically associated with a decrease in appetite or weight loss. In fact, children with this condition may have difficulty sleeping or experience weight gain due to increased appetite.

**Clinical Pearl / High-Yield Fact**
Children with hyperkinetic disorder often exhibit a pattern of hyperactivity, impulsivity, and inattention. They may also experience sleep disturbances, appetite changes, or weight gain.

**Correct Answer: D.**