Alagille syndrome (OMIM #118450) is a rare genetic disorder that can affect multiple organ systems of the body including the liver, heart, skeleton, eyes and kidneys. The specific symptoms and severity of Alagille syndrome can vary greatly from one person to another, even within the same family. Some individuals may have mild forms of the disorder while others may have more serious forms. Common symptoms, which often develop during the first three months of life, include blockage of the flow of bile from the liver (cholestasis), yellowing of the skin and mucous membranes (jaundice), poor weight gain and growth, severe itching (pruritis) and pale, loose stools. Additional symptoms include heart murmurs, congenital heart defects, vertebral (back bone) differences, thickening of the ring that normally lines the cornea in the eye (posterior embryotoxon) and distinctive facial features. Most people with Alagille syndrome have mutations in one copy of the JAG1 gene. A small percentage (less than 1 percent) of patients have mutations of the NOTCH2 gene. These mutations are inherited as autosomal dominant traits, however in about half of cases the mutation occurs as a new change ("de novo") in the individual and was not inherited from a parent. The current estimated incidence of ALGS is between 1:30,000 and 1:45,000 with no difference in gender.
The symptoms and severity of Alagille syndrome can vary greatly from one person to another, even among members of the same family. Some individuals may have a mild form of the disorder that can virtually go unnoticed; other individuals may have a serious form of the disorder that can potentially cause life-threatening complications. It is important to note that affected individuals may not have all of the symptoms discussed below. Affected individuals should talk to their physician and medical team about their specific case, associated symptoms and overall prognosis.
Alagille syndrome can be associated with abnormalities of the liver, heart, eyes, skeleton, kidneys and other organ systems of the body. A main finding of Alagille syndrome is liver disease that often becomes apparent within the first three months of life. However, in individuals with mild liver involvement, a diagnosis may not be made into later in life. Liver disease in Alagille syndrome, if present, may range in severity from jaundice or mild cholestasis to severe, progressive liver disease that can potentially result in liver failure.
Approximately 90 percent of individuals with Alagille syndrome have a reduced number of bile ducts (bile duct paucity) within the liver. Bile ducts are small tube-like structures that carry bile from the liver to the small intestines. The formation of bile is one of the functions of the liver. Bile is a fluid that contains water, certain minerals that carry an electric charge (electrolytes), and other materials including bile salts, phospholipids, cholesterol, and an orange-yellow pigment (bilirubin) that is a byproduct of the natural breakdown of the hemoglobin of red blood cells. Bile flow accomplishes two important tasks within the body: it aids in digestion and absorption of dietary fats, vitamins, and other nutrients and helps eliminate excess cholesterol, bilirubin, waste, and toxins from the body. Therefore, a problem with bile flow often results in malabsorption of vital nutrients and the accumulation of toxic materials in the body.
Because of the reduced number of bile ducts, individuals with Alagille syndrome can develop jaundice and cholestasis usually during the first four months of life. Cholestasis refers to reduced or obstructed flow of bile from the liver. Cholestasis can cause yellowing of the skin and whites of the eyes (jaundice), itching (pruritus) that may be intense, pale-colored stools, dark urine, fatty sores or bumps (xanthomas) just under the surface of the skin, and an abnormally enlarged liver (hepatomegaly) and/or enlarged spleen (splenomegaly). Because the body cannot properly absorb fats and fat-soluble vitamins (vitamins A, D, E, and K), affected children may also experience growth deficiencies and failure to thrive. Malabsorption of vital nutrients can also lead to rickets, a condition marked by softened, weakened bones (vitamin D deficiency), vision problems (vitamin A deficiency), poor coordination and developmental delays (vitamin E deficiency) and blood clotting problems (vitamin K deficiency).
In approximately 15 percent of patients, progressive liver disease results in scarring of the liver (cirrhosis) and liver failure. There is no way to tell which children are at risk for serious, progressive liver disease in Alagille syndrome.
Many individuals with Alagille syndrome have heart (cardiac) abnormalities that can range from benign heart murmurs to serious structural defects. A heart murmur is an extra sound that is heard during a heartbeat. Heart murmurs in children with Alagille syndrome are usually caused by narrowing of the blood vessels of the lungs (pulmonary artery stenosis). Some children with Alagille syndrome may have complex heart defects, the most common of which is tetralogy of Fallot. Tetralogy of Fallot is a rare form of cyanotic heart disease. Cyanosis is abnormal bluish discoloration of the skin and mucous membranes that occurs due to low levels of circulating oxygen in the blood. Tetralogy of Fallot consists of a combination of four different heart defects: ventricular septal defect, obstructed outflow of blood from the right ventricle to the lungs due to an abnormal narrowing of the opening between the pulmonary artery and the right ventricle of the heart (pulmonary stenosis), displaced aorta that causes blood to flow into the aorta from both the right and left ventricles, and abnormal enlargement of the right ventricle.
Additional heart defects that can occur in Alagille syndrome include ventricular septal defects, atrial septal defects, patent ductus arteriosus, and coarctation of the aorta. Some studies have shown that in rare cases there is an association with WolffParkinson-White syndrome, a condition characterized by electrical disturbances in the heart. (For more information on these disorders, choose the specific disorder name as your search term in the Rare Disease Database.)
Some individuals with Alagille syndrome may have eye (ocular) abnormalities, especially posterior embryotoxon, a condition marked by thickening of the ring that normally lines the cornea in the eye. The cornea is the thin, transparent membrane that covers the eyeballs. In most cases, posterior embryotoxon is a benign finding that primarily helps to establish a clinical diagnosis and vision is usually unaffected, although mild decreases in the clarity of vision may occur. Less commonly, other eye abnormalities may occur such as Axenfeld anomaly, a condition in which strands of the iris are abnormally attached to the cornea, or progressive degeneration of the retina (pigmentary retinopathy). The retina is the thin layers of nerve cells that lines that inner surface of the back of the eyes and senses light and converts it to nerve signals, which are then relayed to the brain through the optic nerve.
Individuals with Alagille syndrome usually have distinctive facial features including deeply-set and widely spaced (hypertelorism) eyes, a pointed chin, broad forehead, and low-set, malformed eyes. In older individuals and adults, the chin may appear larger and more prominent (prognathia). Skeletal abnormalities may occur in some individuals with Alagille syndrome including butterfly vertebrae, a condition in which certain bones of the spinal column are irregularly-shaped. This condition is often noted on an x-ray, but usually does not cause any symptoms or problems (asymptomatic).
Additional symptoms may occur in some individuals with Alagille syndrome including kidney (renal) abnormalities, pancreatic insufficiency, vascular anomalies, mild developmental delays and cognitive impairment. Kidney abnormalities may be more prevalent in individuals with Alagille syndrome caused by mutations in the NOTCH2 gene and include abnormally small kidneys, the presence of cysts on the kidneys and decreased or impaired kidney function. The pancreas is a small organ located behind the stomach that secretes enzymes that travel to the intestines and aid in digestion. The pancreas also secretes other hormones such as insulin, which helps to break down sugar. Pancreatic insufficiency is when the pancreas cannot produce or transport enough enzymes to the intestines to aid in the breakdown and absorption of food and nutrients.
Individuals with Alagille syndrome can also develop abnormalities of certain blood vessels (vascular anomalies) including those in the brain, liver, lungs, heart, and kidneys. Vascular anomalies in the brain can lead to bleeding inside the brain (intracranial bleeding) and stroke. Some individuals with Alagille syndrome have developed a condition known as Moyamoya syndrome. Moyamoya syndrome is a progressive disorder that is characterized by narrowing (stenosis) and/or closing (occlusion) inside the skull of the carotid artery, the major artery that delivers blood to the brain. Intracranial bleeding and other vascular anomalies are potentially life-threatening complications and account for a significant percentage of mortality and morbidity in Alagille syndrome.