**Core Concept**
Wormian bones are small, irregular bones found within the sutures of the skull. They are considered a normal variant and are often seen in the lambdoid suture. However, their presence can also be associated with various pathological conditions.

**Why the Correct Answer is Right**
Wormian bones are formed due to the abnormal resorption of bone tissue within the sutures of the skull. This process can occur due to the uneven growth of the skull bones, leading to the formation of small, irregular bones. Wormian bones are often seen in conditions that affect the growth and development of the skull, such as rickets, osteogenesis imperfecta, and Down syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** While rickets can cause various skeletal abnormalities, including Wormian bones, it is not the only condition associated with their presence. However, rickets is indeed associated with Wormian bones.
**Option B:** Osteogenesis imperfecta is a genetic disorder that affects the production of collagen, leading to fragile bones and various skeletal abnormalities, including Wormian bones. Therefore, this option is incorrect.
**Option C:** Down syndrome is a genetic disorder that affects physical and mental development, and individuals with Down syndrome are at a higher risk of developing various skeletal abnormalities, including Wormian bones. Therefore, this option is incorrect.

**Clinical Pearl / High-Yield Fact**
Wormian bones are often seen in the lambdoid suture and can be a normal variant. However, their presence can also be associated with various pathological conditions, such as rickets, osteogenesis imperfecta, and Down syndrome.

**Correct Answer: C. Osteogenesis imperfecta is not typically associated with Wormian bones.**