Symptoms & Recognizing High Ammonia

Recognizing the signs of high ammonia (hyperammonemia) is one of the most important skills you will develop as you manage NAGS deficiency. Ammonia is a toxin that primarily affects the brain, meaning the symptoms usually show up as changes in how a person acts, thinks, or moves ^[1][2].

Ammonia levels can change rapidly. These symptoms often appear during times of catabolic stress—periods when the body breaks down its own protein for energy, such as during an infection, fever, fasting, or after surgery ^[3][4].

Symptoms in Newborns (Neonatal Onset)

In babies born with a severe lack of the NAGS enzyme, symptoms usually appear within the first few days of life ^[1]. Because these signs can look like other common newborn issues, such as a severe infection (sepsis), it is critical to check ammonia levels quickly ^[5][6].

• Poor Feeding: A baby may have a weak suck or show no interest in feeding ^[5].
• Lethargy: Extreme sleepiness where the baby is difficult to wake ^[6].
• Hypotonia: Often described as “floppiness” or low muscle tone ^[7].
• Respiratory Distress: Changes in breathing patterns, such as fast breathing or grunting ^[5].
• Temperature Changes: The baby may have difficulty staying warm (hypothermia) ^[5].

If not treated immediately, these symptoms can progress quickly to irritability, seizures, and eventually a state of unresponsiveness or coma ^[7][2].

Symptoms in Children and Adults (Late-Onset)

Some people have a “partial” deficiency, meaning their enzyme works a little bit. In these cases, symptoms may not appear for months or even decades ^[8]. These symptoms are often episodic, meaning they come and go, usually triggered by illness or stress ^[4].

• Recurrent Headaches: These may be severe and are often accompanied by nausea and vomiting ^[9].
• Behavioral Changes: Sudden irritability, agitation, or “acting out” that is out of character ^[9].
• Confusion and Disorientation: Difficulty following a conversation, “brain fog,” or appearing dazed ^[2][4].
• Avoidance of Protein: Some people naturally develop a “protein aversion,” instinctively avoiding meat or high-protein foods because they make them feel unwell ^[10].
• Altered Consciousness: Extreme drowsiness or appearing “drunk” even without alcohol ^[4].

For women with late-onset NAGS deficiency, the period immediately after childbirth (postpartum) is a high-risk time for a sudden spike in ammonia due to the intense physical stress on the body ^[4][11].

The “Red Flags”: When to Act Immediately

Hyperammonemia is a medical emergency because high ammonia can cause brain swelling ^[7][12]. Do not wait for a callback or test result if you notice severe signs. You should call emergency services (911) or go directly to the nearest emergency department if you observe:

1. Vomiting that prevents keeping medication down ^[12].
2. Sudden confusion, severe disorientation, or extreme personality changes ^[9].
3. Unusual lethargy, marked somnolence, or difficulty staying awake ^[6].
4. Seizures or loss of consciousness.

When heading to the hospital, bring your carglumic acid and your metabolic emergency letter with you if they are readily available.

While it is frightening to watch for these signs, remember that with consistent use of carglumic acid, many people with NAGS deficiency maintain stable ammonia levels and do not experience these symptoms regularly ^[1][13]. Your goal is to learn your (or your child’s) “normal” baseline so you can spot the subtle changes early.