Description
Hereditary pancreatitis is a genetic condition characterized by recurrent episodes of inflammation of the pancreas (pancreatitis). The pancreas produces enzymes that help digest food, and it also produces insulin, a hormone that controls blood sugar levels in the body. Episodes of pancreatitis can lead to permanent tissue damage and loss of pancreatic function.
Signs and symptoms of this condition usually begin in late childhood with an episode of acute pancreatitis. A sudden (acute) attack can cause abdominal pain, fever, nausea, or vomiting. An episode typically lasts from one to three days, although some people may experience severe episodes that last longer. Hereditary pancreatitis progresses to recurrent acute pancreatitis with multiple episodes of acute pancreatitis that recur over a period of at least a year; the number of episodes a person experiences varies. Recurrent acute pancreatitis leads to chronic pancreatitis, which occurs when the pancreas is persistently inflamed. Chronic pancreatitis usually develops by early adulthood in affected individuals. Signs and symptoms of chronic pancreatitis include occasional or frequent abdominal pain of varying severity, flatulence, and bloating. Many individuals with hereditary pancreatitis also develop abnormal calcium deposits in the pancreas (pancreatic calcifications) by early adulthood.
Years of inflammation damage the pancreas, causing the formation of scar tissue (fibrosis) in place of functioning pancreatic tissue. Pancreatic fibrosis leads to the loss of pancreatic function in many affected individuals. This loss of function can impair the production of digestive enzymes and disrupt normal digestion, leading to fatty stool (steatorrhea), weight loss, and protein and vitamin deficiencies. Because of a decrease in insulin production due to a loss of pancreatic function, about a quarter of individuals with hereditary pancreatitis will develop type 1 diabetes mellitus by mid-adulthood; the risk of developing diabetes increases with age.
Chronic pancreatic inflammation and damage to the pancreas increase the risk of developing pancreatic cancer. The risk is particularly high in people with hereditary pancreatitis who also smoke, use alcohol, have type 1 diabetes mellitus, or have a family history of cancer. In affected individuals who develop pancreatic cancer, it is typically diagnosed in mid-adulthood.
Complications from pancreatic cancer and type 1 diabetes mellitus are the most common causes of death in individuals with hereditary pancreatitis, although individuals with this condition are thought to have a normal life expectancy.
Frequency
Hereditary pancreatitis is thought to be a rare condition. In Europe, its prevalence is estimated to be 3 to 6 per million individuals.
Causes
PRSS1 Gene
The PRSS1 gene provides instructions for making an enzyme called cationic trypsinogen. This enzyme is a serine peptidase, which is a type of enzyme that cuts (cleaves) other proteins into smaller pieces. Cationic trypsinogen is produced in the pancreas and helps with the digestion of food. Cationic trypsinogen is secreted by the pancreas and transported to the small intestine, where it is cleaved to form trypsinogen. When the enzyme is needed, trypsinogen is cleaved again into its working (active) form called trypsin. Trypsin aids in digestion by cutting protein chains at the protein building blocks (amino acids) arginine or lysine, which breaks down the protein. Trypsin also turns on (activates) other digestive enzymes that are produced in the pancreas to further facilitate digestion.
A particular region of trypsin is attached (bound) to a calcium molecule. As long as trypsin is bound to calcium, the enzyme is protected from being broken down. When digestion is complete and trypsin is no longer needed, the calcium molecule is removed from the enzyme, which allows trypsin to be broken down.
It is estimated that 65 to 80 percent of people with hereditary pancreatitis have mutations in the PRSS1 gene. Within the single gene, more than 40 mutations have been found. Most of these mutations change single protein building blocks (amino acids) in cationic trypsinogen. Some PRSS1 gene mutations result in the production of a cationic trypsinogen enzyme that is prematurely converted to trypsin while it is still in the pancreas. Other mutations prevent trypsin from being broken down. The most common PRSS1 gene mutation that causes hereditary pancreatitis replaces the amino acid arginine with the amino acid histidine at position 122 in the enzyme (written Arg122His or R122H). As a result of this mutation, the enzyme is not able to be broken down, even when it is no longer bound to calcium.
Trypsin activity in the pancreas can damage pancreatic tissue and can also trigger an immune response, causing inflammation in the pancreas and leading to episodes of pancreatitis.
Inheritance Patterns
When hereditary pancreatitis is caused by mutations in the PRSS1 gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the PRSS1 gene mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.
It is estimated that 20 percent of people who have the altered PRSS1 gene never have an episode of pancreatitis. (This situation is known as reduced penetrance.) It is unclear why some people with a mutated gene never develop signs and symptoms of the disease.
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