Can You Have GA-1 With a Normal Newborn Screen?

Yes. A child can still have Glutaric Acidemia Type 1 (GA-1) even if their newborn screening test came back completely normal ^[1][2]. While newborn screening is an incredible tool that catches most babies with GA-1, it is not perfect ^[1][3]. A specific group of children with GA-1 are what doctors call “low-excretors,” meaning their bodies don’t build up high enough levels of the specific markers the newborn screen looks for ^[4][5]. If your child’s head is growing faster than normal (macrocephaly) or they have a larger-than-average head size, this is a known early red flag for GA-1 that should prompt doctors to look closer, regardless of the screening results ^[6][1].

Understanding the “Low-Excretor” Type

Newborn screening for GA-1 usually looks for elevated levels of a chemical called glutarylcarnitine (also known as C5DC) in your baby’s blood ^[1][2]. In most babies with GA-1, this chemical builds up very quickly.

However, some children with GA-1 have a “low-excretor” biochemical profile ^[4]. Because of their specific genetic makeup, their C5DC levels stay near normal or fall just under the cut-off point used by screening programs ^[5][7][8]. Because their blood levels don’t trigger the alarm, their screening test is reported as normal, leading to a false-negative result ^[5][9].

It is crucial to understand that being a “low-excretor” does not mean the child has a milder form of the disease ^[10][4]. Like all children with GA-1, they are at high risk for serious neurological injury. These injuries are usually triggered by common childhood illnesses, fevers, or fasting—often called a metabolic crisis ^[6]. However, there is a very hopeful side to this: when diagnosed early, GA-1 is highly treatable using a specialized diet, supplements, and emergency protocols during illnesses.

Why a Large Head (Macrocephaly) Matters

A larger-than-average head size—or macrocephaly—is often one of the earliest physical signs of GA-1 ^[6][1]. In babies with GA-1, the large head is typically caused by extra fluid spaces forming around the brain, not necessarily brain swelling or a larger brain itself ^[6][11]. The large head itself is not inherently dangerous, but it is a critical warning sign.

While many healthy babies naturally have large heads, macrocephaly combined with other subtle signs should raise suspicion for GA-1, even if the newborn screen was normal ^[6][2]. Babies with GA-1 might also have temporary episodes of floppiness (hypotonia), developmental delays, or unusual stiff movements (dystonia) ^[6][11][10]. Because false-negative screens do happen, doctors must rely on physical signs like macrocephaly to realize that further testing is needed ^[1][3].

Waiting for Answers: An Important Safety Warning

If your child is currently being tested for suspected GA-1, they are in a vulnerable window. If your baby gets sick, runs a fever, vomits, or stops feeding while you are waiting for test results, go to the Emergency Room immediately. Tell the emergency doctors that your child is being evaluated for Glutaric Acidemia Type 1 and may need IV fluids with glucose to prevent a metabolic crisis.

Next Steps: How Doctors Confirm GA-1 After a Normal Screen

If GA-1 is suspected, your general pediatrician will likely need to refer you to a pediatric metabolic specialist or biochemical geneticist. They will not rely on repeating the newborn blood spot test. Instead, they should order specialized follow-up tests:

• Genetic Testing: A blood or saliva test that reads your child’s DNA to look for mutations in the GCDH gene. This is the absolute most accurate way to confirm GA-1, especially for low-excretors who hide well on other tests ^[2][8][12].
• Urine Organic Acid Analysis: A specialized urine test. While it looks for different chemicals (glutaric acid and 3-hydroxyglutaric acid), be aware that even in the urine, these markers can sometimes still be deceptively low or tricky to interpret in low-excretors ^[10][13].
• Brain MRI: An imaging scan of the brain. In children with GA-1, MRIs frequently show a very specific pattern of fluid build-up or brain changes, often described by radiologists as a “bat-wing” appearance or bilateral arachnoid cysts ^[10][11][6]. Note: Doctors should not wait for visible MRI changes to test for GA-1, as early diagnosis aims to prevent brain damage before it starts.

If you are concerned, do not let a “normal” newborn screen stop you from advocating for your child and asking for these more specific diagnostic tests.