**Core Concept**
The patient's presentation suggests a systemic disorder involving multiple organ systems, including the skin, musculoskeletal, gastrointestinal, and endocrine systems. This condition is likely caused by an abnormal accumulation of a specific substance that affects various bodily functions.

**Why the Correct Answer is Right**
The patient's symptoms are characteristic of **Gaucher's disease**, a genetic disorder caused by a deficiency of the enzyme glucocerebrosidase. This enzyme is responsible for breaking down glucocerebroside, a lipid molecule, into glucose and ceramide. The accumulation of glucocerebroside in cells leads to the formation of Gaucher cells, which are characteristic of the disease. The liver enlargement (hepatosplenomegaly) is due to the accumulation of these cells in the spleen and liver. The hyperpigmentation is likely due to the accumulation of lipids in the skin, leading to a darkening of the skin. The arthritis and hyperglycemia are secondary to the metabolic disturbances caused by the disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not match the patient's presentation. The symptoms described do not suggest a diagnosis of **Wilson's disease**, which is characterized by liver disease, Kayser-Fleischer rings, and neuropsychiatric symptoms.
* **Option B:** This option is incorrect because it does not match the patient's presentation. The symptoms described do not suggest a diagnosis of **Niemann-Pick disease**, which is characterized by severe neurological symptoms, including seizures and loss of motor skills.
* **Option C:** This option is incorrect because it does not match the patient's presentation. The symptoms described do not suggest a diagnosis of **Familial Hypercholesterolemia**, which is characterized by high levels of LDL cholesterol and premature cardiovascular disease.

**Clinical Pearl / High-Yield Fact**
Gaucher's disease is an autosomal recessive disorder that affects 1 in 20,000 to 1 in 50,000 individuals. It is caused by mutations in the GBA gene, which encodes the glucocerebrosidase enzyme. Enzyme replacement therapy is the standard treatment for Gaucher's disease.

**Correct Answer:** C.