Hereditary fructose intolerance

Hereditary fructose intolerance is a rare inherited metabolic disorder in which the body lacks a functioning enzyme needed to properly break down fructose, a sugar found in fruit, some vegetables, and many processed foods and drinks. Without this enzyme, consuming fructose leads to a toxic build-up of a specific intermediate substance in the liver, causing symptoms and potential organ damage. It is usually identified in infancy, often when fruit or fructose-containing foods are first introduced to the diet.

It is caused by inherited mutations in the ALDOB gene, which codes for the enzyme aldolase B needed to metabolise fructose, following an autosomal recessive inheritance pattern requiring a faulty gene copy from each parent. It is present from birth as a genetic condition, though symptoms only appear once fructose-containing foods are introduced to the diet. It is not related to lifestyle or dietary choices in its origin, only in its symptomatic trigger.

Symptoms include nausea, vomiting, abdominal pain, and low blood sugar shortly after consuming fructose-containing foods, and with ongoing exposure, poor growth, liver problems, and kidney effects. Infants often develop symptoms when weaning onto solid foods containing fruit or added sugars. Interestingly, many affected infants and children develop a strong natural aversion to sweet foods, which can be a helpful early clue.

Yes, ongoing exposure to fructose without dietary management can cause significant liver and kidney damage over time, and severe acute reactions can cause dangerously low blood sugar. With strict, lifelong avoidance of fructose, sucrose (which contains fructose), and sorbitol, most people with this condition are healthy and develop normally. The main danger comes from continued exposure in someone whose diagnosis is not recognised or properly managed.

Yes, it is an autosomal recessive genetic condition, meaning both parents must carry a faulty copy of the gene for a child to be affected. Genetic testing can confirm the diagnosis, and carrier testing can be offered to family members. Siblings of an affected child should also be considered for testing, given the inheritance pattern.

The main treatment is strict, lifelong dietary avoidance of fructose, sucrose, and sorbitol, requiring careful reading of food labels since these sugars are present in many processed foods as well as fruit. Dietitian support is important, particularly in helping families navigate hidden sources of fructose and ensure adequate nutrition despite the restrictions. With good adherence to this diet, most people with the condition have excellent long-term health.

There is no cure for the underlying enzyme deficiency, but with strict dietary avoidance of fructose throughout life, people with this condition can be entirely healthy with normal growth and development. The condition does not resolve or improve with age; dietary avoidance remains necessary for life. Regular dietitian and specialist metabolic follow-up helps ensure the diet remains nutritionally adequate as needs change with age.

Hereditary fructose intolerance is a rare, serious genetic enzyme deficiency that can cause significant organ damage with continued fructose exposure, requiring strict lifelong dietary avoidance. Fructose malabsorption (sometimes called fructose intolerance in a more general sense) is a much more common and generally less serious digestive issue where the gut has difficulty absorbing fructose, causing bloating and discomfort but not the same risk of organ damage. These are genuinely different conditions with very different levels of seriousness, despite the similar-sounding names, so accurate diagnosis matters considerably.

Care is coordinated by a specialist metabolic team and dietitian from diagnosis, typically in infancy, with regular scheduled reviews to monitor growth, nutrition, and organ health. Any accidental exposure to fructose-containing foods causing symptoms should be discussed with the specialist team. Lifelong follow-up, rather than discharge once diagnosed, remains the standard approach for this condition.