The Path to a Diagnosis: Understanding Labs and Genetic Tests

Confirming a diagnosis of SSADHD is often a careful process that combines biochemical “clues” from your child’s body fluids with a “blueprint” check of their DNA. Understanding these tests can help you navigate the diagnostic journey and make sense of complex laboratory reports.

The Pillars of Diagnosis

A definitive diagnosis involves complementary evidence that is carefully interpreted by a metabolic or genetics specialist. This typically includes one and/or both of the following:

1. Biochemical Testing: Finding high levels of specific chemicals in the urine or blood ^[1].
2. Genetic Testing: Identifying two pathogenic or likely pathogenic changes (mutations) in the ALDH5A1 gene—one inherited from each parent ^[2].

Note: In the right clinical context, strongly suggestive genetic findings can sometimes establish a diagnosis even if biochemical results are equivocal, and vice-versa.

Urine and Blood Testing: Why Age Matters

The primary “red flag” for SSADHD is an elevation of GHB (4-hydroxybutyric acid) ^[2]. However, where and when you test for it is critical:

• Urine is Preferred: Urine organic acid analysis is the most common screening tool. In children with SSADHD, GHB levels in the urine are usually markedly high ^[1][3].
• The Blood-Age Gap: If your doctor tests your child’s blood (plasma) or a dried blood spot, the results must be interpreted carefully based on age. Research shows that GHB levels in the blood naturally decline as a child grows, reaching a low point (nadir) around age 10 ^[4][5].
• The Risk of “Normal” Results: Because of this age-related decline, an older child with SSADHD might have blood GHB levels that appear near the normal range ^[5]. For this reason, a “normal” or borderline blood test does not necessarily rule out the condition ^[4].

Understanding 4,5-DHHA on Your Report

You may see a chemical called 4,5-dihydroxyhexanoic acid (or 4,5-DHHA) listed on a metabolic report.

• What it is: This is a byproduct that forms when the normal breakdown of GABA is blocked ^[2].
• Is it specific to SSADHD? While it is often elevated in children with SSADHD, it is not a “perfect” marker. High levels of 4,5-DHHA can also be seen in people with mitochondrial diseases or during a severe internal infection called sepsis ^[6]. Doctors must look at this result alongside other findings to be sure of the diagnosis ^[7].

Decoding Genetic Reports: The VUS Challenge

Genetic testing for SSADHD looks for mutations in the ALDH5A1 gene. Sometimes, the report is clear (listing “pathogenic” or “likely pathogenic” variants). Other times, it returns a Variant of Uncertain Significance (VUS) ^[8].

A VUS means the lab found a change in the DNA, but science doesn’t yet know if that specific change actually causes the disease or if it is just a harmless natural variation ^[9]. A VUS alone should never be used to guide treatment or make reproductive decisions.

To help clarify a VUS, doctors may use:

• Parental Testing: Testing both parents establishes “phase”—whether the child inherited one variant from each parent (known as being in trans) ^[1]. While helpful, this alone does not prove the VUS is disease-causing.
• Enzyme Activity or Protein Expression Tests: Specialized research laboratories can measure how well the SSADH enzyme is working, or if the body is making the protein at all ^[10]. If activity is very low, it provides strong supportive evidence for expert interpretation, though it is not a guaranteed resolution ^[9][8].

If genetic testing only finds one mutation but biochemical tests strongly suggest SSADHD, your doctor should also consider deletion/duplication testing to look for larger missing pieces of the gene that standard sequencing might miss ^[11].