Description
Alagille syndrome is a rare autosomal dominant genetic disorder affecting the liver, heart, and other systems of the body. The condition is characterised by a paucity of intrahepatic bile ducts causing cholestasis, along with congenital heart disease, characteristic facies, skeletal abnormalities, and ocular and renal involvement.
Pathogenesis
Alagille syndrome results from mutations in the JAG1 gene (90-95% of cases) or the NOTCH2 gene (less than 1% of cases). These genes encode proteins involved in the Notch signalling pathway, which is essential for embryonic development. Mutations result in aberrant development of the structures derived from the embryonic foregut, mainly the liver and heart, but also affecting the eyes, skeleton, and kidneys.
Epidemiology, Risk Factors & Associations
- Incidence is approximately 1 in 30,000 to 1 in 70,000 live births.
- No known sex, ethnic or geographical predisposition.
- Associated with cardiac defects, especially peripheral pulmonary stenosis and Tetralogy of Fallot.
- Family history is an important risk factor due to its autosomal dominant inheritance.
Clinical Features
- Cholestatic jaundice typically appears in infancy.
- Pruritus due to cholestasis.
- Characteristic facies: deep-set eyes, a broad forehead, a straight nose, and a pointed chin.
- Congenital heart disease, most commonly peripheral pulmonary stenosis.
- Skeletal abnormalities: butterfly vertebrae, tall stature, and hyperextensible joints.
- Ocular abnormalities: posterior embryotoxon in the eye.
Complications
- Progressive liver disease leading to cirrhosis.
- Nutritional deficiencies due to malabsorption.
- Growth retardation.
- Renal involvement: renal tubular acidosis, renal cysts.
Pathological Features
Histopathology
- Ductopaenia: Liver biopsy reveals a paucity of intrahepatic bile ducts.
Genetics
- Mutations in the JAG1 gene (located on chromosome 20) are present in 90-95% of cases.
- Rarely, mutations in the NOTCH2 gene (located on chromosome 1) are seen.
Radiological Features
General Features
- Liver: Hepatomegaly and cirrhotic changes with disease progression.
- Heart: Structural abnormalities, particularly pulmonary artery stenosis and Tetralogy of Fallot.
- Skeleton: Abnormal vertebral segmentation, especially butterfly vertebrae.
Ultrasound
- Liver: Coarsened echotexture due to chronic cholestasis and fibrosis. Hepatomegaly. Signs of portal hypertension (portal vein enlargement, splenomegaly, varices).
- Heart: Echocardiography can visualise cardiac defects.
- Kidneys: Renal cysts can be identified.
Differential Diagnosis
- Other causes of neonatal jaundice and cholestasis, such as biliary atresia, idiopathic neonatal hepatitis, alpha-1-antitrypsin deficiency.
- Other causes of congenital heart disease.
Management
- Primarily supportive and multidisciplinary, involving gastroenterology, cardiology, genetics, and other specialties as needed.
- Therapies are aimed at managing pruritus, correcting nutritional deficiencies, addressing cardiac anomalies, and monitoring for progression of liver disease.
- Liver transplantation may be required for end-stage liver disease.
- Genetic counselling is essential due to the autosomal dominant inheritance.