The Diagnostic Path for PIGT-related MCAHS3

Confirming a diagnosis of PIGT-related MCAHS3 is often a multi-step process. Because the symptoms—like seizures and developmental delays—can look like many other conditions, doctors use a combination of advanced genetic “blueprints,” blood chemistry, and brain imaging to find the answer ^[1][2].

Genetic Testing: The Definitive Answer

While standard tests like a chromosomal microarray (CMA) are often done first to look for large missing or extra pieces of DNA, they usually cannot find the small “typos” in the PIGT gene ^[2]. To diagnose this condition, more detailed testing is required:

• Whole Exome Sequencing (WES): This test reads the protein-coding parts of all ~20,000 genes. It is often used to find rare conditions like PIGT-CDG, though it can miss deep intronic or structural variants ^[1][3].
• Comprehensive Gene Panels: These are focused tests that look at a specific group of genes known to cause seizures or developmental delays.
• Trio Testing: When possible, doctors prefer to test both parents alongside the child (“trio sequencing”). This helps confirm that the child inherited one changed PIGT gene from each parent, which is necessary for this autosomal recessive condition ^[1][4]. A molecular diagnosis requires appropriate pathogenic or likely pathogenic variants; a Variant of Uncertain Significance (VUS) or a single heterozygous finding does not establish the diagnosis.

Biochemical and Functional Clues

Genetic results are sometimes supported by “functional” tests that show how the gene change is actually affecting the body’s cells.

• Alkaline Phosphatase (ALP): In many children with PIGT variants, a routine blood test shows unusually low ALP levels (hypophosphatasia-like phenotype) ^[5]. However, in some cases, these levels can be high or even normal, so this test alone cannot confirm or rule out the diagnosis ^[6][7].
• Flow Cytometry: This is an optional, specialized blood test that looks at the surface of white blood cells. If the PIGT “tethering” system is broken, the cells will be missing certain proteins (like CD16, CD24, or CD59) ^[5][7]. A specialized marker called FLAER is often used. These are optional, expert-directed functional tests and are not necessarily required for every patient ^[8].

Baseline Neurological and Body Imaging

Once the genetic “why” is found, doctors use other tests to understand the “how” (how the condition is affecting your child right now). It is important to note that EEG and MRI findings are variable and nonspecific; they characterize the condition and its complications rather than confirming the gene diagnosis itself.

• EEG (Electroencephalogram): This records the brain’s electrical activity. While there is no single EEG pattern unique to PIGT, doctors look for signs of seizures or unusual electrical discharges ^[5][9].
• Brain MRI: An MRI may show delayed myelination (a delay in the brain’s “insulation” developing) or progressive atrophy (where parts of the brain, like the cerebellum or brainstem, appear smaller than expected) ^[5][10]. A normal or nonspecific study does not rule the condition in or out.
• Skeletal Survey and Eye Exam: X-rays may be used to check for “delayed bone age,” and a pediatric ophthalmologist will perform a detailed exam to look for structural changes in the eye or retina ^[6][11].

Diagnostic Completeness Checklist

When you receive your child’s reports, ensure the following specific details are included. These are vital for your child’s records and for any future research participation.

If these details are missing, you can ask your genetic counselor or neurologist to provide the “full laboratory report” rather than just the summary letter. Having this data allows you to “audit” the diagnosis and ensures your child’s medical history is as accurate as possible.