User:EBMLibrarian/Alagille syndrome

Alagille syndrome (ALGS) is a genetic disorder that affects primarily the liver and the heart. Problems associated with the disorder generally become evident in infancy or early childhood. The disorder is inherited in an autosomal dominant pattern, and the estimated prevalence of Alagille syndrome is 1 in every 30,000 to 1 in every 40,000 live births. It is named after the French pediatrician Daniel Alagille, who first described the condition in 1969. Children with Alagille syndrome live to the age of 18 in about 90% of the cases.

Signs and symptoms

The severity of the disorder can vary within the same family, with symptoms ranging from so mild as to go unnoticed, to severe heart and/or liver disease that requires transplantation. It is uncommon, but Alagille syndrome can be a life-threatening disease with a mortality rate of 10%. The majority of deaths from ALGS are typically due to heart complications or chronic liver failure. citation needed

Common signs of Alagille syndrome include congenital heart problems varying from heart murmurs to significant structural abnormalities, such as Tetralogy of Fallot, Pulmonary Stenosis, overriding aorta, ventricular septal defect, and right ventricular hypertrophy are common amongst Alagille patients. Patients may also present with Ventricular septal defect, Atrial septal defect, Patent ductus arteriosus, and Coarctation of the aorta. The mortality rate of Tetralogy of Fallot when untreated ranges from 70% by age 10 to 95% by age 40. However, complete surgical repair can significantly improve both longevity and quality of life in patients with Alagille syndrome. citation needed

JAG1 and NOTCH2 encode for proteins that are crucial to the notch gene–signaling cascade. Specifically, JAG1 encodes for a surface-binding ligand that regulates the notch signaling pathway. It plays a crucial role in cell signaling during embryonic development. If the pathway is disrupted due to mutations, an infant will not develop properly. Alagille syndrome causes bile duct paucity, which is characterized by narrow and malformed bile ducts. Bile duct paucity causes bile to build up in the liver, resulting in scarring of the liver which hinders the liver's normal functions, like blood filtration and drug metabolism.

The notch gene–signaling cascade is also important for cell–cell recognition, which involves gene regulation mechanisms that control multiple cell differentiation processes during embryonic and adult life, and is specially important for:

• Atrioventricular (AV) canal development
• Ventricular development
• Ventricle (heart) outflow tract development
• Angiogenesis
• Pancreatic development
• Intestinal development
• Bone development
• Respiratory system development
• Neuron cell differentiation
• Neurite development
• Gliogenesis
• Adult brain function

Diagnosis

Alagille syndrome can be extremely difficult to diagnose. While people are born with ALGS, it is almost always diagnosed later during childhood. The diagnosis can be difficult because the severity of the disease varies widely among patients. Some common clinical tests that are run in order to diagnose the disease include vertebral x-rays, heart exams to detect any defects such as a heart murmur, and a liver biopsy to detect liver disease or any precursors. If a patient presents with multiple symptoms such as jaundice, heart murmur, and the characteristic facial features discussed above (deep set eyes, broad brow, etc.), they are likely to be diagnosed with Alagille syndrome. A more calculated and specific diagnosis can be done with genetic testing. Next-generation sequencing can be utilized to detect single nucleotide polymorphisms (SNPs) in the affected gene(s). Multiplex ligation-dependent probe amplification (MLPA) can detect large deletions and/or insertions and microarray comparative genomic hybridization is used to improve the accuracy of MLPA.

Treatment

Early treatment is possible once the disease is diagnosed. Treatments of Alagille syndrome typically involve medications, therapies, and/or surgical procedures. All treatments aim to improve bile excretion from the liver, reduce pain caused by the disease, and help improve nutritional deficiencies. Diet can also be a crucial factor in improving quality of life when living with ALGS.

Medication

Several medications are used to improve bile flow, including ursodiol (Actigall or Urso). These medications differ in their rates of success. Certain drugs may be used to reduce itching (pruritus), such as cholestyramine and rifampin. While these medications can reduce pruritus, the itching often is reduced when bile flow is improved via ursodiol or liver transplant.

Many patients with Alagille syndrome have nutritional and/or malabsorption issues which often hinders normal growth. Patients benefit from vitamin A, D, E, and K supplements because the reduced bile flow makes it difficult to absorb and utilize these vitamins. A high-calorie diet is very important, and often requires a gastrostomy tube to maintain the high caloric intake.

Maralixibat (Livmarli) was approved for medical use in the United States in September 2021.

Surgery

Surgery is common in more severe cases on Alagille syndrome, especially for patients with liver disease or end-stage liver failure. Liver transplants can either be a complete liver transplant from a deceased organ donor, or a partial transplant from a living donor. Liver transplants can be difficult in ALGS patients because heart defects are common along with the liver failure, and such intense surgeries are dangerous for cardiac patients because they cannot handle the stress of surgery and general anesthesia.

Partial biliary diversion has been used to significantly reduce pruritus, jaundice, and xanthoma caused by poor bile flow in patients with bile duct paucity. A portion of the bile produced by the liver is directed through a surgically created stoma into a plastic pouch on the patient's lower right abdomen. The pouch is periodically drained as it fills with bile. Patients with biliary atresia may require a Kasai procedure to improve bile drainage; however, later liver transplantation is still often necessary.