**Core Concept**
Scheuermann's disease is a type of vertebral body deformity characterized by an abnormal kyphotic (forward-rounded) curvature of the thoracic spine, often resulting from a failure of vertebral body growth and endplate ossification. It typically affects adolescents and young adults.

**Why the Correct Answer is Right**
Scheuermann's disease is a result of abnormal growth and development of the vertebral endplates, leading to a failure of vertebral body growth. This causes an abnormal curvature of the thoracic spine, which can lead to back pain, stiffness, and decreased mobility. The condition is often associated with vertebral body wedging and Schmorl's nodes, which are herniations of the nucleus pulposus through the endplate into the adjacent bone.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option does not accurately describe Scheuermann's disease, which is a specific type of vertebral deformity.

**Option B:**
This option describes a different condition, such as scoliosis, which is a lateral curvature of the spine.

**Option C:**
This option is incorrect, as Scheuermann's disease is not an autoimmune disorder.

**Clinical Pearl / High-Yield Fact**
Scheuermann's disease is often associated with a characteristic "gibbus" deformity, which is a forward-rounded curvature of the thoracic spine. This can be a key clinical finding on physical examination.

**Correct Answer: C. Scheuermann's disease is a type of vertebral body deformity characterized by an abnormal kyphotic (forward-rounded) curvature of the thoracic spine.**