A bone turns black primarily due to a rare genetic disorder called Alkaptonuria (AKU), also known as Black Bone Disease.
Understanding Alkaptonuria (AKU)
Alkaptonuria is a metabolic disorder where the body cannot properly break down homogentisic acid (HGA). This is due to a mutation in the HGD gene, which is responsible for producing the enzyme homogentisate 1,2-dioxygenase. This enzyme's job is to break down HGA.
The Role of Homogentisic Acid (HGA)
When HGA isn't properly broken down, it accumulates in the body, particularly in cartilage and connective tissues. Over time, this accumulation leads to:
- Ochronosis: A bluish-black pigmentation of cartilage and other tissues.
- Bone Discoloration: The accumulated HGA eventually causes bones to turn black, making them brittle and prone to fractures.
- Arthritis: Severe joint pain and stiffness, especially in the spine and large joints.
- Other Complications: HGA can also affect the heart, kidneys, and other organs.
Summary of Alkaptonuria
| Feature | Description |
|---|---|
| Cause | Mutation in the HGD gene, leading to a deficiency in homogentisate 1,2-dioxygenase |
| Accumulation | Homogentisic acid (HGA) |
| Key Symptom | Blackening of bones and cartilage (Ochronosis) |
| Other Symptoms | Arthritis, heart problems, kidney stones |
