Symptoms and Emergency Protocols

Because Fanconi-Bickel Syndrome (FBS) affects how your child’s body handles fuel and filters waste, common childhood experiences like a stomach bug or a long stretch of sleep can quickly become medical emergencies. Recognizing the early physical signs and knowing when to seek urgent help are the most critical tools for managing this condition.

How FBS Appears in Infancy

In the first months of life, FBS often presents with a cluster of physical symptoms caused by the liver’s inability to release sugar and the kidney’s “leakiness.”

• Hepatomegaly (Enlarged Liver): This is one of the most common signs ^[1]. You may notice your baby has a very large, firm, and distended belly ^[2]. This happens because sugar is trapped inside the liver as glycogen.
• Failure to Thrive: Infants with FBS often struggle to gain weight and may have a significant “linear growth deficit,” meaning they are much shorter than other children their age ^[3][4].
• Hypophosphatemic Rickets: Because the kidneys leak phosphorus—a mineral vital for bone strength—the bones can become soft or bowed ^[3]. This is known as rickets, and it may cause delayed walking or physical discomfort ^[5].

The Blood Sugar Swings

Unlike many other conditions, FBS causes a unique pattern called dysglycemia, where the body swings between two extremes ^[6].

1. Fasting Hypoglycemia (Low Sugar): Between meals or overnight, the liver cannot release trapped sugar into the blood. This leads to low blood sugar, which can cause shakiness, irritability, or extreme lethargy ^[7].
2. Postprandial Hyperglycemia (High Sugar): Shortly after eating, blood sugar may spike very high ^[3]. This happens because the GLUT2 transporter that should pull sugar out of the blood and into the liver is impaired ^[6].

It is important to note that glucosuria (sugar in the urine) primarily reflects the kidney’s inability to reabsorb glucose ^[3]. This means sugar will leak into the urine even when blood sugar is normal or low, completely independently of the high post-meal spikes.

Sick Day Rules and Emergency Protocols

For a child with FBS, a simple cold, ear infection, or stomach bug puts extra stress on the body, making it harder to maintain stable sugar levels. During infections, liver enzymes (AST and ALT) can spike significantly, reflecting liver stress ^[8].

You must have a written sick-day protocol from your metabolic team. While every child’s plan is unique, general guidelines include:

• If the child is alert and can drink: Continue frequent oral feeds or fast-acting carbohydrates as prescribed by your team. Check blood sugar frequently. Note that Continuous Glucose Monitor (CGM) readings may lag during rapid changes and should be confirmed with a finger-stick test ^[7][9].
• If the child is vomiting or refusing to eat: They are at immediate risk of a metabolic crash. Do not wait for them to become lethargic. Proceed to the emergency department for hospital-grade IV glucose ^[10][11].
• If the child is unconscious or seizing: Do NOT give food or liquid by mouth. Call emergency services (911) immediately.

Red Flags: When to Seek Emergency Care

In FBS, a metabolic crisis can happen rapidly. Seek emergency medical evaluation immediately if you notice:

• Signs of Severe Hypoglycemia: Extreme sleepiness, difficulty waking up, seizures, or loss of consciousness ^[12].
• Persistent Vomiting or Diarrhea: If your child cannot keep down their prescribed cornstarch or frequent meals ^[10].
• Rapid, Deep Breathing: This can be a sign of metabolic acidosis, where the blood becomes too acidic because the kidneys are leaking bicarbonate ^[1].
• Extreme Weakness: This may indicate hypokalemia (dangerously low potassium levels) or hypophosphatemia (low phosphorus) ^[9][13].
• Dehydration: Dry mouth, no tears when crying, or fewer wet diapers than usual.

Always carry your child’s Emergency Protocol Letter from their metabolic specialist. This letter will instruct the ER team on your child’s specific, individualized IV glucose concentration and fluid needs ^[8]. Never rely on generic IV fluids; the treating team must follow the metabolic specialist’s explicit instructions.