Mapping the Diagnosis: Imaging, Labs, and Genetics

Diagnosing Leigh syndrome is often described as a “diagnostic odyssey”—a journey through various tests to find a specific answer. Because this syndrome can be caused by mutations in over 100 different genes, doctors use a combination of “footprints” (MRI and blood work) and the “blueprint” (genetic testing) to confirm the diagnosis ^[1][2].

The MRI “Footprint”

An MRI is often the first tool used when Leigh syndrome is suspected. Doctors look for specific patterns in the brain that suggest energy failure.

• Bilateral, Symmetrical Lesions: This is the “classic” finding. It refers to areas of cellular stress or damage that appear on both sides of the brain in the exact same spots ^[3][4].
• Basal Ganglia and Brainstem: These are the areas most commonly affected because they require the most energy to manage movement and basic life functions like breathing ^[3][5].
• Important Note: A “normal” MRI does not completely rule out Leigh syndrome. In some patients, the characteristic lesions may not appear until later in the disease or may be located in other areas like the cerebellum ^[3][6].

Metabolic Markers: Lactate and Pyruvate

When the “power plants” (mitochondria) in the cells aren’t working properly, they can’t burn fuel (glucose) cleanly. This leads to a buildup of “exhaust” in the body, which doctors measure through blood or cerebrospinal fluid (CSF) tests ^[7].

• Lactate: High levels of lactate often indicate that the cells are forced to use an inefficient backup system to create energy because the main system is failing ^[7][4].
• Pyruvate: This is a molecule the body uses to make energy. The ratio between lactate and pyruvate can help doctors narrow down which specific part of the energy production line is broken ^[8].

Genetic Testing: The Definitive Answer

While MRIs and blood tests provide clues, genetic testing is the only way to get a definitive diagnosis ^[9]. Finding the specific gene involved is vital for several reasons:

1. Identifying Treatable Subtypes: Some rare forms of Leigh-like syndrome, such as PDHC deficiency or SLC19A3 defects, may respond to high doses of vitamins like thiamine (B1) or biotin ^[10][8].
2. Ending the Odyssey: Tests like Whole Exome Sequencing (WES) or Whole Genome Sequencing (WGS) look at thousands of genes at once to find the exact “glitch” ^[11][12]. Practically, these tests usually just require a simple blood draw or a cheek swab from the patient and sometimes their parents.
3. Future Planning: Knowing the gene (e.g., SURF1, LRPPRC, MT-ATP6, NDUFS4) tells doctors whether the mutation was inherited from both parents or just the mother, which is essential for family planning ^[13][14].

Understanding Your Diagnostic Report

You may see these terms on your medical reports:

• Pathogenic Variant: A genetic change that is known to cause disease ^[13].
• VUS (Variant of Uncertain Significance): A genetic change has been found, but scientists aren’t sure yet if it causes the disease or is just a normal human variation ^[11].
• Leigh-like Syndrome: Used when a patient has many symptoms of Leigh syndrome, but their MRI or genetic tests don’t perfectly match the “classic” definition ^[15].

Empowerment Checklist

• [ ] Request a copy of the MRI report. Look for the words “symmetrical,” “basal ganglia,” or “brainstem.”
• [ ] Ask for the genetic test results. Ensure you know if it was a “Mitochondrial Panel,” “WES,” or “WGS.”
• [ ] Check for thiamine-responsiveness. Ask your doctor if the specific mutation is one that could benefit from targeted vitamin supplementation ^[8].
• [ ] Monitor lactate levels. Keep a log of these levels during routine checkups and when ill.