Crigler-Najjar syndrome

Background

• Crigler-Najjar syndrome (CNS) is a rare autosomal recessive disorder of bilirubin metabolism caused by absent (type 1) or severely reduced (type 2) UGT1A1 enzyme activity, resulting in severe unconjugated hyperbilirubinemia from birth. Type 1 is a life-threatening neonatal emergency — without aggressive phototherapy and ultimately liver transplantation, the accumulation of unconjugated bilirubin causes kernicterus (irreversible bilirubin-induced brain damage). Type 2 (Arias syndrome) is milder and manageable with phenobarbital.
• The emergency physician may encounter CNS as persistent severe neonatal jaundice unresponsive to standard phototherapy, or as an acute bilirubin crisis in a known CNS patient triggered by illness, fasting, or surgery.
• Extremely rare: estimated ~100 known type 1 cases worldwide at any given time; type 2 is somewhat more common
• Higher prevalence in the Amish and Mennonite communities (founder effect)
• Exists on a spectrum with Gilbert syndrome — all three conditions involve UGT1A1 mutations but differ in severity:

Feature	CN type 1	CN type 2 (Arias)	Gilbert syndrome
UGT1A1 activity	Absent	Markedly reduced (<10% of normal)	Reduced (~30% of normal)
Bilirubin level	20-50 mg/dL (can exceed 50)	6-20 mg/dL	Typically <3 mg/dL (rarely to 6)
Kernicterus risk	Very high — constant threat	Rare but possible (illness, anesthesia)	None
Response to phenobarbital	None (critical diagnostic distinction)	Yes (reduces bilirubin ~25%)	Yes (but not needed)
Treatment	Phototherapy 10-16 hours/day + liver transplant	Phenobarbital ± phototherapy	None required
Prognosis	Fatal without transplant; brain damage risk	Survival into adulthood; near-normal life	Normal lifespan; benign

Mechanism

• UGT1A1 enzyme conjugates bilirubin with glucuronic acid → water-soluble conjugated bilirubin → excreted in bile
• In CN type 1: complete absence of UGT1A1 activity → no conjugation → unconjugated bilirubin accumulates to dangerous levels
• In CN type 2: severe reduction (<10%) of UGT1A1 activity → some conjugation occurs → lower bilirubin levels
• Unconjugated bilirubin is lipophilic and crosses the blood-brain barrier → deposits in basal ganglia, brainstem nuclei, cerebellum → kernicterus

Clinical features

CN type 1 — the neonatal emergency

• Severe jaundice within the first days of life — total bilirubin typically 20-50 mg/dL; entirely unconjugated
• All other liver function tests completely normal (AST, ALT, alkaline phosphatase, albumin, coagulation studies)
• No evidence of hemolysis (normal reticulocyte count, haptoglobin, LDH, smear)
• Jaundice is persistent and progressive despite standard neonatal phototherapy
• Does NOT respond to phenobarbital — this distinguishes CN1 from CN2 and is a critical diagnostic feature
• Without treatment, kernicterus develops — often within the first weeks to months of life

Acute bilirubin encephalopathy (early kernicterus) — ED emergency signs

• Lethargy, poor feeding, hypotonia (early)
• High-pitched cry
• Fever
• Irritability progressing to opisthotonus (arching of the back/neck — hypertonia)
• Seizures
• Apnea/respiratory failure
• Coma
• This is a medical emergency — bilirubin-induced brain damage may become irreversible within hours

Chronic bilirubin encephalopathy (established kernicterus)

• Choreoathetoid cerebral palsy (extrapyramidal movement disorder)
• Upward gaze palsy
• Sensorineural hearing loss (auditory neuropathy)
• Dental enamel hypoplasia
• Cognitive function often relatively preserved

CN type 2 (Arias syndrome) — milder presentation

• Intermittent mild-to-moderate jaundice (bilirubin 6-20 mg/dL)
• Typically diagnosed later in childhood or adolescence
• Jaundice worsens with illness, fasting, stress, surgery, anesthesia
• Responds to phenobarbital (bilirubin decreases ~25% within 2-3 weeks)
• Kernicterus is rare but has been reported, especially during intercurrent illness or general anesthesia
• Most patients survive into adulthood without neurologic damage

Known CNS patient presenting to the ED

• Bilirubin crisis precipitated by:
  • Intercurrent illness (infection, febrile illness)
  • Fasting/dehydration
  • Surgery/general anesthesia (bilirubin may rise dramatically perioperatively)
  • Noncompliance with phototherapy (CN1)
  • Discontinuation of phenobarbital (CN2)
• May present with worsening jaundice, signs of early encephalopathy, or family concern about rising bilirubin levels

Differential diagnosis

Severe neonatal unconjugated hyperbilirubinemia

• Crigler-Najjar syndrome type 1 (bilirubin >20 mg/dL; no hemolysis; phenobarbital unresponsive)
• Crigler-Najjar syndrome type 2 (bilirubin 6-20 mg/dL; phenobarbital responsive)
• Hemolytic disease of the newborn (Rh/ABO incompatibility, G6PD deficiency, hereditary spherocytosis) — positive Coombs test, elevated reticulocytes, abnormal smear
• Physiologic/breastfeeding jaundice — resolves; bilirubin typically <15 mg/dL
• Gilbert syndrome — bilirubin typically <6 mg/dL; does not cause kernicterus alone
• Sepsis — other systemic signs present
• Hypothyroidism — prolonged jaundice; check TSH

Key distinguishing feature of CN type 1

• Bilirubin >20 mg/dL that is entirely unconjugated + normal liver function + no hemolysis + no response to phenobarbital = CN type 1 until proven otherwise

Evaluation

ED workup

• Fractionated bilirubin (total and direct): confirms purely unconjugated hyperbilirubinemia
• Hepatic panel: AST, ALT, alkaline phosphatase, GGT, albumin — must be entirely normal (liver is structurally and functionally intact in CNS)
• Coagulation studies: PT/INR — normal (unless neonate has other vitamin K-related issues)
• CBC with reticulocyte count and peripheral smear: to exclude hemolysis
• Haptoglobin, LDH: normal (no hemolysis)
• Direct Coombs test: negative (excludes immune-mediated hemolysis)
• Blood type (mother and infant): to evaluate for ABO/Rh incompatibility
• TSH: to exclude hypothyroidism
• Blood glucose: neonates with severe jaundice may have concurrent hypoglycemia

Confirmatory testing (arrange via specialist)

• Phenobarbital trial: the most practical bedside distinguishing test between CN1 and CN2; phenobarbital (3-5 mg/kg/day for 2-3 weeks) will reduce bilirubin in CN2 but not in CN1
• UGT1A1 gene sequencing: confirms diagnosis and distinguishes type 1 from type 2
• Bile analysis: near-complete absence of bilirubin conjugates in bile confirms CN1 (available via duodenal aspiration; not an ED test)

Management

Acute bilirubin crisis (CN1 patient or any patient with bilirubin approaching kernicterus threshold)

• Intensive phototherapy: initiate immediately
  • Blue LED light (wavelength 460-490 nm)
  • Maximize body surface area exposure (undress the infant; use overhead and underneath light sources)
  • Phototherapy converts unconjugated bilirubin into water-soluble photoisomers that can be excreted without conjugation
• Exchange transfusion: if bilirubin is at or above the exchange transfusion threshold for age, or if signs of acute bilirubin encephalopathy are present
  • Rapidly removes circulating unconjugated bilirubin
  • Double-volume exchange (twice the infant's blood volume)
• Plasmapheresis: alternative to exchange transfusion in older children/adults; effectively removes unconjugated bilirubin
• IV albumin: binds free unconjugated bilirubin in the blood and may reduce the fraction crossing the blood-brain barrier; give 1 g/kg IV before exchange transfusion
• Aggressive IV fluid hydration with dextrose-containing fluids
• Treat precipitating illness: antibiotics if infection; correct dehydration; resume nutrition
• Avoid drugs that displace bilirubin from albumin: sulfonamides, ceftriaxone, salicylates — these increase free (unbound) unconjugated bilirubin and worsen kernicterus risk

Ongoing management of CN type 1

• Daily phototherapy: 10-16 hours per day, lifelong (until liver transplant)
  • Phototherapy becomes less effective with age as skin thickens and body surface area-to-volume ratio decreases — this creates increasing risk of kernicterus around puberty
• Liver transplantation: the only definitive cure for CN type 1
  • Transplanted liver has normal UGT1A1 activity → bilirubin normalizes
  • Post-transplant survival: 86-100% at 1 year, 79-92% at 10 years
  • Prophylactic transplant is recommended before kernicterus develops, as kernicterus may not be reversible
  • Timing is difficult because onset of neurologic damage is unpredictable
• Hepatocyte transplantation: experimental; temporary reduction (~50%) in bilirubin; may bridge to transplant
• Gene therapy: AAV-mediated UGT1A1 gene delivery is in clinical trials; promising but not yet standard of care
• Adjunctive medications: calcium phosphate (bilirubin binder in gut), orlistat (reduces enterohepatic circulation), vitamin E, CoQ10, L-carnitine

Management of CN type 2

• Phenobarbital: 3-5 mg/kg/day; reduces bilirubin by ~25% through UGT1A1 enzyme induction; this is the mainstay of therapy
• Phototherapy during acute exacerbations
• Liver transplantation rarely needed
• Avoid triggers: fasting, dehydration, intercurrent illness
• Perioperative planning: inform anesthesia and surgery teams; bilirubin may rise dramatically with general anesthesia; optimize phenobarbital, ensure phototherapy availability, consider perioperative albumin infusion

Disposition

• Neonate with suspected CN type 1 (severe unconjugated hyperbilirubinemia unresponsive to standard phototherapy):
  • NICU admission
  • Continuous intensive phototherapy
  • Exchange transfusion if at threshold or encephalopathy present
  • Genetics/metabolic and hepatology consultation
  • Early referral to liver transplant center
• Known CN1 patient with bilirubin crisis:
  • Admit (ICU if encephalopathy signs present)
  • Intensive phototherapy; exchange transfusion/plasmapheresis if bilirubin critically elevated
  • Identify and treat trigger
  • Contact the patient's hepatologist/metabolic specialist
• Known CN2 patient with jaundice exacerbation:
  • Ensure phenobarbital is being taken and at therapeutic levels
  • Treat precipitating illness
  • Phototherapy if bilirubin significantly elevated
  • May be managed as outpatient if bilirubin is well below encephalopathy threshold and patient is clinically well; close follow-up
• General precautions for all CNS patients:
  • Carry a medical alert identification
  • Inform all healthcare providers of the diagnosis
  • Avoid medications that displace bilirubin from albumin (sulfonamides, ceftriaxone, salicylates)
  • Avoid prolonged fasting
  • Surgical/anesthetic procedures require advance planning with the metabolic team

See Also

• Gilbert syndrome
• Neonatal jaundice
• Neonatal hepatitis
• Kernicterus
• Hemolytic disease of the newborn
• G6PD deficiency

External Links

• StatPearls — Crigler-Najjar Syndrome
• Expert Opin Orphan Drugs — Management of Crigler-Najjar syndrome (2021)
• American Liver Foundation — Crigler-Najjar Syndrome
• Int J Mol Sci — Therapeutic Options for Crigler-Najjar Syndrome: A Scoping Review (2024)
• Cureus — Liver Transplantation in a Child With Crigler-Najjar Syndrome Type I (2023)