**Question:** All are seen in metachromatic leukodystrophy except –

A. Hypomyelination
B. Normal myelination
C. Subacute sclerosing panencephalitis
D. Leukodystrophy with spastic paraparesis

**Core Concept:** Metachromatic Leukodystrophy (MLD) is a rare, inherited disorder affecting the myelin sheath surrounding nerve fibers in the central nervous system (CNS). MLD is characterized by a deficiency of arylsulfatase A enzyme, which leads to the accumulation of sulfatides and other glycolipids in the CNS, causing progressive neurological decline.

**Why the Correct Answer is Right:**

The correct answer is "B. Normal myelination" because normal myelination is the process by which the white matter in the brain forms and maintains the myelin sheath around nerve fibers. In MLD, there is a deficiency of arylsulfatase A enzyme, which results in the accumulation of sulfatides and other glycolipids in the CNS. This accumulation leads to the destruction of myelin sheath and subsequent neurological impairment, not normal myelination.

**Why Each Wrong Option is Incorrect:**

A. Hypomyelination: Hypomyelination refers to a decrease in the thickness or number of myelin sheaths around nerve fibers. In metachromatic leukodystrophy, the issue lies in the accumulation of sulfatides and other glycolipids, not a decrease in myelin thickness.

C. Subacute sclerosing panencephalitis (SSPE): SSPE is a progressive neurological disorder caused by the persistence of measles virus in the brain. It is not related to the accumulation of sulfatides and glycolipids seen in metachromatic leukodystrophy.

D. Leukodystrophy with spastic paraparesis: Leukodystrophies are a group of disorders characterized by the destruction of the myelin sheath, which is not seen in MLD due to sulfatides and glycolipids accumulation.

**Clinical Pearl:**

In cases where you come across a question involving neurological disorders, always consider the specific enzymatic defect, pathological changes, and clinical features associated with the disorder. This understanding helps to differentiate between various leukodystrophies and other neurological conditions. A thorough knowledge of the pathophysiology and clinical presentation will assist in identifying the correct diagnosis and treatment approach.