Adult-Onset Leukodystrophies
Ranked by relative frequency in adult-onset genetic leukoencephalopathy cohorts and population prevalence estimates. Below the first tier, all entities are rare in absolute terms.
Most Common
- FXTASHighest raw prevalence; approximately 1:3,000 men over 50 after estimated premutation frequency and penetrance. Technically a repeat-expansion neurodegeneration with white matter involvement.
- CADASILMost common monogenic small-vessel disease; clinical prevalence approximately 2–5 per 100,000 and a leading diagnosis in inherited leukoencephalopathy series.
- X-ALD / AMNMost common true leukodystrophy at any age; birth incidence approximately 1:15,000–20,000 including heterozygotes. AMN is the dominant adult phenotype.
- CSF1R-Related Leukoencephalopathy (ALSP)Approximately 10–25% of adult-onset leukodystrophies in genetic series; still underdiagnosed and may mimic MS, FTD, or CBS.
Relatively Frequent
- Adult-Onset MLDMLD overall is approximately 1:40,000–160,000; about 20% present after age 16.
- CTXApproximately 1:50,000 by allele frequency, with higher frequency in East Asian and Moroccan Jewish populations; heavily underdiagnosed.
- NIIDHundreds of genetically confirmed cases in Japan and China since 2019; rivals CADASIL in some Asian series but remains sporadic in European ancestry.
- Other Mitochondrial LeukoencephalopathiesFrequent as a category because mitochondrial disease is approximately 1:5,000, although each leukoencephalopathy-predominant genotype is rare.
Rare
- Adult-Onset KrabbeApproximately 5–10% of Krabbe disease; overall approximately 1:100,000–250,000.
- Adult-Onset Alexander DiseaseApproximately 1:2.7 million by a Japanese estimate.
- COL4A1/2 Small-Vessel DiseaseSecond most frequent monogenic SVD after CADASIL, but hundreds of families rather than thousands.
- APBDA few hundred cases; relatively frequent in the Ashkenazi founder population.
- Adult-Onset VWMVWM is approximately 1:80,000 births; adult onset is a small minority.
- LMNB1-ADLDApproximately 50 families worldwide.
- LBSLMore than 100 cases; adult diagnosis is relatively common for its size.
- L-2-HGAApproximately 300 cases; the slow course often permits adult diagnosis.
- Sjögren–Larsson SyndromeApproximately 1:250,000; higher in the Swedish founder region.
- Mild/Adult PMDPMD is approximately 1:200,000–500,000 males; adult presentation is uncommon.
Very Rare
- CARASILApproximately 100 cases, mostly Japanese or Chinese.
- Labrune Syndrome (LCC)Fewer than 100 cases.
- AARS2Approximately 50 cases.
- CLCN2A few dozen cases.
- Gordon Holmes SyndromeA few dozen cases.
- AMACR DeficiencyFewer than 40 cases.
- POLR3-Related HLDApproximately 150 or more overall; adult/mild forms are a handful.
- MLCApproximately 300 overall; adult presentation is exceptional.
- PMLDFewer than 100 cases; adult presentation is exceptional.
- Juvenile/Atypical CanavanA few dozen cases.
- PADMALApproximately a dozen families.
- AARS1 Adult LeukoencephalopathySingle-digit reported cases.
Interpretive Caveats
Ancestry can substantially shift the ranking, particularly for NIID, APBD, CARASIL, and CTX. CSF1R-related disease and NIID continue to move upward as testing spreads, so their tier assignments are the most likely to change.
Source note: Disease profiles are adapted from the supplied study guide based on Muthusamy et al. (2023). Frequency tiers reflect the cohort and prevalence estimates supplied for this ranking. Treatment statements reflect the 2023 publication and are not an updated therapeutic review.