Leukodystrophy

A genetically determined disorder affecting the white matter of the central nervous system, typically progressive, often involving myelin formation, maintenance, or turnover. The presentation depends on age and the dominant pattern: infants with hypotonia, spasticity, and macrocephaly; school-age children with gait disturbance and academic decline; adolescents and adults with progressive spasticity, ataxia, cognitive change, or behavioral / psychiatric symptoms. Many leukodystrophies have an extraneural footprint (adrenal in X-ALD, peripheral nerve in MLD, eye in MLD adult, gonadal in vanishing white matter) that helps narrow the differential and changes management.

Two pieces of data do more diagnostic work than anything else:

1. Age of onset. Infantile (< 1 year), late-infantile (1-3), juvenile (3-10), adolescent (10-18), adult (> 18). Each band has a characteristic differential, and the same gene can produce very different syndromes at different ages (X-ALD childhood-cerebral vs adult adrenomyeloneuropathy; MLD late-infantile vs juvenile vs adult).
2. MRI pattern. Leukodystrophy MRI is pattern recognition in a way few other neurogenetic workups are. The first pass identifies the dominant region, then layers on enhancement, contrast pattern, and extra-white-matter findings.

Always front-load the treatable forms. Cerebrotendinous xanthomatosis, biotinidase deficiency, X-linked adrenoleukodystrophy (HSCT for cerebral form), and metachromatic leukodystrophy (HSCT, atidarsagene autotemcel gene therapy) all have disease-modifying options that work only if started early. Diagnostic delay is morbidity.

A workable first cut on MRI:

Treatable (test these first)

• Cerebrotendinous xanthomatosis (CYP27A1): juvenile to adult onset; chronic diarrhea, juvenile cataracts, tendon xanthomas, progressive ataxia and dementia. White matter changes and dentate signal abnormality. Chenodeoxycholic acid is disease-modifying and dramatically alters course if started early.
• Biotinidase deficiency: infantile / late-infantile leukoencephalopathy with seizures, alopecia, dermatitis, optic atrophy. Treatable with biotin.
• X-linked adrenoleukodystrophy (ABCD1) cerebral form: HSCT halts cerebral disease if performed before significant clinical or radiographic progression. This is the leukodystrophy where diagnostic urgency is highest. Boys 4-10 years with behavioral / academic decline → VLCFAs today.
• Metachromatic leukodystrophy (ARSA, AR): HSCT (presymptomatic) and atidarsagene autotemcel gene therapy (approved for early- and late-infantile forms in many regions) are available; outcomes depend on early treatment.

Infantile (< 1 year)

• Krabbe disease (GALC): infantile globoid cell leukodystrophy. Irritability, hypertonia, optic atrophy, regression, peripheral neuropathy. Cherry-red macula absent. HSCT in the presymptomatic period is the only disease-modifying option; newborn screening has expanded in several US states.
• Canavan disease (ASPA, AR): macrocephaly + infantile-onset hypotonia evolving to spasticity + frontal-predominant T2 white matter changes. Ashkenazi Jewish founder mutations. NAA elevated on urine and MRS.
• Alexander disease (GFAP, mostly de novo dominant): macrocephaly, seizures, regression, frontal-predominant white matter disease, brainstem involvement. Rosenthal fibers on histology.
• Megalencephalic leukoencephalopathy with subcortical cysts (MLC, MLC1): macrocephaly + temporal subcortical cysts on MRI, mild course relative to imaging.
• Vanishing white matter disease / CACH (EIF2B 1-5): infantile to adult; characteristic episodic deteriorations triggered by minor head trauma or febrile illness, progressing to cystic degeneration of white matter. Ovarian failure is the extra-CNS feature (ovarioleukodystrophy).

Late-infantile and juvenile (1-10 years)

• Metachromatic leukodystrophy (ARSA, AR): late-infantile form most common; gait disturbance, peripheral neuropathy, regression. Juvenile form: behavioral / academic decline first, then motor. Diffuse symmetric white matter with subcortical sparing; tigroid pattern. Arylsulfatase A pseudodeficiency is a common confounder; confirm with urinary sulfatides plus enzyme + genetics.
• X-linked adrenoleukodystrophy cerebral form: boys 4-10 years; behavioral and academic decline, then visual / auditory deficits, gait, spasticity, swallowing. Adrenal insufficiency may precede or follow CNS disease. Parieto-occipital MRI pattern with enhancement at advancing edge.
• Pelizaeus-Merzbacher disease (PLP1, X-linked): boys, nystagmus in infancy, hypotonia, then progressive spasticity, ataxia. Severe forms with neonatal presentation; classic with childhood onset. Diffuse hypomyelination on MRI.
• 4H syndrome / POL3-related leukodystrophy (POLR3A, POLR3B): hypomyelination + hypodontia + hypogonadotropic hypogonadism. Cerebellar findings, dental abnormalities, delayed puberty.
• Aicardi-Goutières syndrome: infantile-onset encephalopathy with calcifications, white matter disease, chilblains, and an interferon signature (interferonopathy). Mimics congenital infection.

Adolescent and adult

• Adult X-linked adrenoleukodystrophy (adrenomyeloneuropathy, AMN): spastic paraparesis, sphincter dysfunction, adrenal insufficiency. Slowly progressive over decades. Female carriers can develop AMN-like myelopathy in midlife.
• Adult-onset metachromatic leukodystrophy: psychiatric / behavioral changes, executive dysfunction, then motor; often misdiagnosed as primary psychiatric disease for years.
• Adult Alexander disease: bulbar / brainstem-predominant with palatal myoclonus and ataxia, sometimes with cervical cord atrophy.
• Adult vanishing white matter: more chronic course with episodic worsening with infection or trauma.
• Cerebrotendinous xanthomatosis: dementia, ataxia, dystonia, neuropathy, tendon xanthomas. Treatable.

Other inherited white-matter disorders

• GM1 / GM2 gangliosidoses, NPC, Gaucher type III: lysosomal disease with white matter involvement.
• Fabry disease: small-vessel white matter changes, not classic leukodystrophy.
• Mitochondrial leukoencephalopathy (Leigh syndrome, MELAS, Kearns-Sayre, POLG): secondary white matter disease with characteristic gray-matter and brainstem involvement.
• CADASIL (NOTCH3): adult small-vessel vasculopathy with anterior temporal pole and external capsule T2 changes, migraines with aura, recurrent strokes, dementia. Not a classic leukodystrophy but on the white-matter differential.

1. MRI brain (with contrast and spectroscopy if available). Pattern recognition is half the diagnosis. Repeat imaging if disease is progressive and initial pattern is non-specific.
2. VLCFAs: any boy with leukodystrophy, any unexplained adult-onset spastic paraparesis (women too, since carriers can develop AMN), any new childhood-onset behavioral decline. Cheap, fast, and the test that catches the most actionable disease.
3. Lysosomal enzyme panel: arylsulfatase A (MLD, with confirmatory urinary sulfatides because pseudodeficiency is common), galactocerebrosidase (Krabbe), beta-galactosidase (GM1), hexosaminidase A and B (Tay-Sachs, Sandhoff).
4. Biotinidase activity if any treatable-cause features (rash, alopecia, seizures).
5. Cholestanol (CTX).
6. Plasma amino acids, urine organic acids, urinary N-acetylaspartate (NAA elevated in Canavan), lactate, plasma very-long-chain plasmalogens (peroxisomal).
7. CSF studies: glucose (GLUT1), lactate, interferon panel (Aicardi-Goutières), neopterins.
8. EMG / nerve conduction: peripheral neuropathy in MLD, Krabbe, AMN, mitochondrial.
9. Adrenal function (ACTH-stimulated cortisol): mandatory if X-ALD on the differential.
10. Targeted genetic testing → leukodystrophy gene panel → exome. ABCD1, ARSA, GALC, ASPA, GFAP, PLP1, EIF2B1-5, POLR3A/POLR3B, MLC1, CYP27A1, NOTCH3, and many others.