Diagnostic Tests, Biomarkers, and Newborn Screening

Navigating the lab reports and imaging results following a Krabbe diagnosis can feel like learning a new language. These tests are the tools doctors use to determine which subtype of the disease your child has and how quickly they need to move toward treatment.

The Most Important Number: Psychosine Levels

While missing the GALC enzyme starts the process, the buildup of a toxic lipid called psychosine is what causes the damage. Today, doctors consider psychosine levels the most reliable biomarker (a measurable indicator of disease) for predicting how the disease will progress ^[1][2].

• Infantile Range ($\ge$ 10 nmol/L): Levels at or above this threshold strongly suggest the aggressive, early infantile form of the disease ^[1].
• Late-Onset Range (2–10 nmol/L): Levels in this middle range typically indicate a slower-progressing form (Late Infantile, Juvenile, or Adult) ^[1].
• Carrier Range (<2 nmol/L): These levels are usually seen in “carriers”—people who have one mutated gene but will never develop the disease themselves ^[1].

Understanding Your Genetic Report

The GALC gene provides instructions for making the enzyme that clears out toxins. When you look at the genetic report, you may see a mention of the 30-kb deletion ^[3].

• What it is: This is a specific “chunk” of missing DNA in the GALC gene. It is the most common mutation in people of European or Mexican ancestry ^[1][4].
• What it means: If a child has this deletion on both copies of their gene (homozygous), it almost always leads to the severe infantile form ^[1][5].

Imaging and Nerve Tests: Seeing the Damage

Even before a baby shows symptoms, specialized tests can “see” the myelin being stripped away from the nerves.

• MRI (The Brain): Doctors look for white matter hyperintensities—bright spots on the scan that show where the myelin insulation is damaged. In Krabbe, these are often found in the periventricular (middle) and cerebellar (back) parts of the brain ^[6][7].
• Nerve Conduction Studies (The Body): This test measures how fast electrical signals travel through the nerves in the arms and legs. In Krabbe, these signals are significantly slowed because the “insulation” (myelin) is missing ^[1].
• BAER and VEP: These tests measure how the brain responds to sound (BAER) and light (VEP). They help establish a baseline for your child’s hearing and vision ^[1].

Newborn Screening: A Race Against Time

In states that screen for Krabbe, the goal is to identify babies before they show any symptoms ^[1].

• Why speed matters: For the best outcomes, a stem cell transplant should ideally happen before 30 days of age ^[1].
• The Process: If the initial heel-prick shows low enzyme activity, the lab immediately runs a psychosine test and genetic sequencing to confirm the diagnosis ^[2][8].

Your Completeness Checklist

Ensure your child’s medical team has performed or scheduled the following for a full diagnostic picture:

• [ ] GALC Enzyme Activity: Measured in white blood cells (leukocytes) ^[9].
• [ ] Psychosine Level: A blood test to predict disease speed ^[1].
• [ ] GALC Gene Sequencing: To identify specific mutations and the 30-kb deletion ^[9].
• [ ] Brain MRI: To check for white matter changes ^[6].
• [ ] Neurophysiology Tests: Nerve Conduction Study (NCS), BAER, and VEP ^[1].
• [ ] Lumbar Puncture: To check for elevated protein in the spinal fluid ^[10].