Confirming the Diagnosis: MRI, Genetics, and Labs

Confirming a diagnosis of AARS2-related leukoencephalopathy is a multi-step process that combines high-tech brain imaging with precise genetic “mapping.” Because this condition is so rare and shares features with other diseases, your care team uses a specific set of tools to reach a definitive answer ^[1][2].

The MRI: Supportive Clues in the White Matter

The first clue often comes from a Magnetic Resonance Imaging (MRI) scan of the brain. Doctors look for a specific “signature” in the white matter, though these patterns are not absolute diagnostic requirements and can vary ^[3].

• Confluent Patterns: The white matter damage usually appears “confluent,” meaning the spots blend together into larger areas. This is most common in the frontoparietal region (the front and top-middle of the brain) ^[1][4].
• Rarefaction: This is a key supportive hallmark. On a specific MRI sequence called FLAIR, the damaged white matter may “suppress” or turn dark. This indicates rarefaction—the tissue has become porous or thin, almost like a sponge ^[3][2].
• U-Fiber Sparing: In AARS2-related disease, the damage often “spares” the subcortical U-fibers. These are the very outermost “loops” of white matter just beneath the brain’s surface. Seeing these fibers remain relatively healthy helps point toward AARS2 ^[3][4].
• Callosal Thinning: The corpus callosum, the bridge connecting the two halves of the brain, often becomes thinner over time ^[1][5].

The Genetic “Gold Standard”

While an MRI can strongly suggest the diagnosis, genetic testing evaluated by a genetics professional is required for confirmation. AARS2 is an autosomal recessive condition, meaning a person must have biallelic mutations—two pathogenic or likely pathogenic variants in the AARS2 gene ^[1][6].

• Testing Types: Doctors may use a targeted “leukodystrophy panel” (testing many white-matter genes at once) or broader tests like Whole Exome Sequencing (WES) or Whole Genome Sequencing (WGS) ^[7][8].
• Deletion/Duplication Analysis: Sometimes a standard sequence test misses a “missing piece” of a gene. If only one mutation is found but symptoms strongly match, doctors may order a specific test to look for these larger deletions ^[6][9].
• Phasing and Parental Testing (Segregation): To be sure the two mutations are on different copies of the gene (one on the copy from mom and one from dad), doctors often test the parents. This is called “segregation analysis” and ensures the mutations are in trans ^[6][10]. A variant of uncertain significance does not confirm the diagnosis.

Gynecologic Evaluation for POI

Because roughly 82% of reported females with this condition experience premature ovarian insufficiency, a reproductive evaluation is highly supportive for people with ovaries—though it is not a requirement for the diagnosis, as the disease also affects males and females without POI ^[1].

• Hormone Labs and Menstrual History: The diagnosis of POI generally relies on the menstrual history combined with appropriately interpreted FSH (Follicle-Stimulating Hormone) testing. In POI, FSH is typically high ^[11][12].
• Estradiol and AMH: Estradiol levels may be checked but can fluctuate. AMH (Anti-Müllerian Hormone) and a pelvic ultrasound (to look at follicles) may be used as adjuncts to assess ovarian reserve, but AMH is not a stand-alone diagnostic test for POI and cannot reliably predict spontaneous conception ^[11][13][14].

The Diagnostic Picture

A diagnosis relies on the full clinical picture interpreted together:

1. Genetic Proof: Two pathogenic or likely pathogenic variants in the AARS2 gene, shown to be in trans ^[1].
2. Supportive Clinical Context: Symptoms like gait changes, cognitive difficulties, or POI ^[1].
3. Supportive MRI: Evidence of frontoparietal white matter changes and/or rarefaction, interpreted in the clinical context ^[3].