**Core Concept**
Reilly bodies are characteristic inclusion bodies found in cells affected by certain genetic disorders. They are particularly associated with lysosomal storage diseases, which result from the accumulation of abnormal substances within lysosomes due to enzyme deficiencies.

**Why the Correct Answer is Right**
Hurler disease, also known as mucopolysaccharidosis type I (MPS I), is a genetic disorder caused by a deficiency of the enzyme alpha-L-iduronidase. This enzyme is crucial for breaking down mucopolysaccharides, or glycosaminoglycans (GAGs). The accumulation of undegraded GAGs within lysosomes leads to cellular dysfunction and the formation of Reilly bodies. These inclusion bodies are composed of aggregated GAGs and are typically found in the cytoplasm of affected cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Gangliosidosis is a lysosomal storage disease, but it is characterized by the accumulation of gangliosides, a type of sphingolipid, rather than mucopolysaccharides. Therefore, it does not typically form Reilly bodies.
**Option B:** Bechet's disease is a form of vasculitis that affects blood vessels and is characterized by inflammation and immune complex deposition, but it is not associated with lysosomal storage or the formation of Reilly bodies.
**Option C:** Gaucher's disease is another lysosomal storage disease, but it is caused by a deficiency of the enzyme glucocerebrosidase, which leads to the accumulation of glucocerebroside rather than mucopolysaccharides. Gaucher cells may contain characteristic sea-blue inclusions, but not Reilly bodies.
**Option D:** This option is the correct answer.

**Clinical Pearl / High-Yield Fact**
Reilly bodies are a key histopathological feature of Hurler disease and can be used to support a diagnosis in affected tissues, such as bone marrow or lymph nodes.

✓ Correct Answer: D. Hurler disease