Hereditary Fructose Intolerance
When I found out I had fructose malabsorption and began researching the topic, hereditary fructose intolerance (HFI) also kept coming up in my searches. I had a flashback to when I was in graduate school because a professor in my old department studies HFI. I knew graduate students in his lab and learned about their research and that the lab also conducts genetic screens to help physicians and genetic counselors determine if their patients have HFI. The reason that fructose malabsorption and HFI both pop up in a google search is that they are both known as a fructose intolerance, however they are very different. Fructose malabsorption affects the digestive system and is not life threatening whereas HFI is a metabolic disorder, which does not involve the digestive system and can be life threatening. This can be very confusing for people when they are first trying to learn about their specific disorder. Because of this possible confusion, I thought it would be interesting and helpful to discuss HFI. I have discussed what is fructose malabsorption and its possible causes in a previous post entitled, What Causes Fructose Malabsorption? Good Question, No Concrete Answer.
Hereditary fructose intolerance (HFI), an inherited disease affecting about 1 in 20,000 people, is when fructose is not properly metabolized in the liver. When we eat foods such as fruit, honey, sucrose, which is made up of half fructose and half glucose, the fructose is absorbed by the small intestine. The inability of the small intestine to absorb fructose is known as fructose malabsorption resulting in digestive and related symptoms. If fructose is properly absorbed by the small intestine it will then enter the liver to be first broken down into fructose-1-phosphate and eventually further metabolized into energy to be used by the body. The gene ALDOB produces aldolase B, which is the enzyme that both breaks down fructose-1-phosphate into its by-products and aids in the breakdown of glycogen, the storage form of glucose in the liver, which is another energy source used by our bodies. It has been demonstrated that HFI patients have a mutated ALDOB gene resulting in either loss of aldolase B production or production of a non-functional aldolase B. A deficiency of aldolase B will lead to a buildup of fructose-1-phosphate in liver cells, which is toxic and can cause long-term damage to the liver. Furthermore, fructose-1-phosphate needs to be further metabolized because its products are required for the production of glucose to stabilize blood sugar levels. Without aldolase B, hypoglycemia occurs.
Since the ALDOB mutation is recessive, individuals may not know that they carry the mutated ALDOB gene and may not have a family member who suffers from HFI. This can be dangerous since HFI is typically first seen in babies when they start on formula, juices, or fruits with fructose. Without knowing that a family member carries the ALDOB mutation, it can prevent the proper diagnosis of HFI. HFI can range from mild to severe so symptoms may vary. In fact, some HFI patients are not diagnosed until they are in adulthood. Symptoms may include abdominal pain, bloating, diarrhea, vomiting, nausea, fever, seizures, hunger, excessive thirst and urination, failure to gain weight and grow, and hypoglycemia. Furthermore, the liver can enlarge and jaundice and cirrhosis may occur. Coma and death may result if HFI is not properly diagnosed or treated.
Babies who survive will develop an aversion to fructose. However, this is difficult to do since fruit, vegetables, and 80% of the processed foods in our food stores contain fructose or sucrose. It is important for HFI patients to avoid fructose, sucrose, and sorbitol, a sugar alcohol, as much as possible to prevent the development of symptoms. Currently, the only treatment is controlling one’s diet. Fortunately, if caught early enough and if fructose is avoided, an HFI patient can live a healthy life.
HFI is a rare disorder but one that needs to be understood well so its symptoms can be prevented early. There are wonderful resources out there to help individuals or families learn more about the disease, including what to look out for and testing information. You can find a few resources below. The first resource is the Dean Tolan lab, the professor from my graduate school.
Photo found on PEXELS