Instantaneous rigor is seen in-
**Core Concept**
Instantaneous rigor, also known as instantaneous rigor mortis, is a rare phenomenon where the body exhibits rigor mortis shortly after death, often within minutes. This is in contrast to the typical 2-4 hours required for rigor mortis to develop in the general population.
**Why the Correct Answer is Right**
Instantaneous rigor is thought to be caused by a genetic mutation affecting the actin-myosin cross-bridge cycling process, which is responsible for muscle contraction and relaxation. In individuals with this mutation, the muscle fibers undergo rigor mortis almost immediately after death due to an abnormality in the RYR1 gene, which encodes the ryanodine receptor involved in calcium release and muscle contraction.
**Why Each Wrong Option is Incorrect**
**Option A:** This is a distractor and does not relate to the correct answer.
**Option B:** This is not a recognized cause of instantaneous rigor mortis.
**Option C:** This is a distractor and does not relate to the correct answer.
**Clinical Pearl / High-Yield Fact**
Instantaneous rigor mortis is a rare condition that can be associated with certain genetic mutations, making it an important consideration in forensic pathology and death investigations.
**Correct Answer: D. Alkaptonuria**