**Core Concept**
Menke disease is a rare, inherited disorder caused by mutations in the ATP7A gene, leading to impaired copper transport and accumulation in various organs. The disease primarily affects the brain, where copper deficiency disrupts normal neuronal function and leads to severe neurological symptoms.

**Why the Correct Answer is Right**
The most common cause of death in Menke disease is due to severe brain dysfunction, which results from the accumulation of toxic copper ions in the brain. This copper overload triggers oxidative stress, inflammation, and neuronal damage, ultimately leading to brain degeneration and death. The brain's inability to maintain proper copper balance and homeostasis leads to a vicious cycle of neuronal damage, resulting in the characteristic symptoms of Menke disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Seizures are a common feature of Menke disease, but they are not the primary cause of death.
**Option B:** While Menke disease does involve the accumulation of toxic copper ions, the kidneys are not the primary organ affected.
**Option C:** While gastrointestinal symptoms can be present in Menke disease, they are not the most common cause of death.

**Clinical Pearl / High-Yield Fact**
It's essential for clinicians to recognize the early signs and symptoms of Menke disease, including failure to thrive, developmental delays, and seizures, to initiate early treatment with copper histidine, which can help manage the disease and improve patient outcomes.

**Correct Answer: B. Sepsis**