Hereditary Fructose Intolerance

Overview

Hereditary fructose intolerance (HFI) is a rare inherited condition that affects how the body handles a type of sugar called fructose. Fructose is the natural sugar found in fruit, honey and many sweetened foods and drinks. People with HFI are born with a missing or faulty liver enzyme (a protein that helps chemical reactions happen) called aldolase B. Without it, the body cannot break fructose down properly. Instead, a breakdown product builds up in the liver and blocks normal sugar release into the blood. This can cause low blood sugar, tummy upset and, over time, liver problems. HFI is not a food allergy and it is not caused by anything a parent did or did not do.

HFI is rare. Estimates vary, but it is thought to affect roughly 1 in 20,000 to 1 in 30,000 people worldwide. Because it is uncommon, many doctors may see only a handful of cases in their whole career, and it is sometimes missed or mistaken for other tummy or feeding problems.

HFI affects boys and girls equally and can occur in any ethnic group. It is caused by a change in a gene that both parents must pass on (this is called an autosomal recessive pattern). Most people with HFI start having symptoms in infancy, when fruit, juice or sweetened foods are first introduced, but some people are only diagnosed in older childhood or adulthood because they naturally avoided sweet foods without realising why.

Symptoms

Common symptoms

• Feeling sick or being sick after eating fruit, juice, honey or sweetened foods and drinks
• Tummy pain, swelling and wind
• Sweating, trembling, shakiness or dizziness after a sweet meal
• Feeling unusually sleepy, weak or foggy, which can be a sign of low blood sugar
• Going off sweet foods completely, or finding them unpleasant
• Yellowing of the skin or eyes (jaundice) in more serious cases
• Feeling generally unwell, with poor appetite and slow weight gain

Symptoms in children

• Poor feeding, refusing bottles or food, and slow weight gain or growth
• Being very sleepy, floppy or irritable after feeds that contain fruit or sweeteners
• Repeated vomiting after weaning onto fruit or sweetened foods
• A swollen tummy and an enlarged liver found by a doctor
• Easy bruising or bleeding, which can happen if the liver is affected
• Seizures or unusual drowsiness during a low blood sugar episode — these need emergency help

Symptoms in older adults

• Many adults with HFI were diagnosed as children and already follow a safe diet
• Some adults are diagnosed late after a lifetime of unexplained tummy upset or a strong dislike of sweet foods
• Adults may notice symptoms after a change in diet, a new medicine, or a product containing hidden sweeteners
• Long-standing, untreated liver irritation can cause tiredness and general poor health, so regular check-ups matter

Causes

Main causes

• HFI is caused by a change (variant) in a gene called ALDOB, which carries the instructions for making the liver enzyme aldolase B.
• It is inherited in an autosomal recessive pattern, meaning a child must receive a changed copy of the gene from both parents to have the condition.
• Parents who each carry one changed copy are usually healthy and often have no idea they are carriers.
• The condition is not caused by diet, lifestyle, infection or anything a parent did during pregnancy.

Risk factors

• Having a brother or sister with HFI
• Parents who are known carriers of an ALDOB gene change
• Parents who are closely related by blood, which raises the chance of both carrying the same rare gene change
• Being from a family or community where the condition has been seen before

When to see a doctor

See a doctor urgently if:

• A baby or child who is very sleepy, floppy, vomiting repeatedly, or not feeding
• Symptoms of low blood sugar that do not settle quickly after eating
• Yellowing of the skin or eyes
• Tummy swelling with pain that is getting worse

Book a routine appointment if:

• Repeated tummy pain, wind or vomiting after fruit, juice or sweet foods
• A strong, lifelong dislike of sweet foods together with tummy symptoms
• A family member has been diagnosed with HFI — ask about testing for yourself or your child
• You are planning a pregnancy and HFI runs in your family

Diagnosis

A doctor will start by asking about symptoms, what foods seem to trigger them, and any family history. If HFI is suspected, you or your child will usually be referred to a specialist, such as a children's doctor or a liver specialist, and often to a dietitian. Diagnosis is confirmed with blood tests and genetic testing. Because HFI is rare, it can take time to reach the answer, and it is reasonable to ask whether testing is needed.

Tests that may be done

• Blood tests to check liver function and blood sugar levels
• Genetic testing of the ALDOB gene, usually from a blood or saliva sample
• Tests to check for other causes of liver problems or tummy symptoms
• A carefully supervised trial of removing fructose and sucrose from the diet to see whether symptoms improve
• Testing of close family members once a gene change is found in one person

What to expect at your appointment

Some tests are quick, while genetic results can take a few weeks. In the meantime, your doctor or dietitian may suggest avoiding fruit, table sugar and sweeteners to see if symptoms settle. Never remove foods from a baby's or child's diet without medical or dietitian advice, because growing children need careful nutrition planning. Ask who will explain the results and what the next steps are.

Treatment

There is no cure for HFI, but it can be managed very well. The main treatment is a lifelong diet that avoids fructose, sucrose (table sugar) and a group of sweeteners called sorbitol and similar sugar alcohols. A registered dietitian with experience of metabolic or inherited conditions should guide the diet, especially for babies and children. Emergency treatment for a severe low blood sugar episode is given in hospital by healthcare professionals.

Self-care at home

• Follow the diet plan your dietitian gives you rather than cutting foods out on your own
• Read food and drink labels every time, as recipes and ingredients change
• Check medicines, vitamins, supplements and dental products with your pharmacist, because some contain sweeteners
• Carry a card or note explaining your condition, especially when travelling or eating out
• Plan meals and snacks ahead so you always have safe options available
• Attend regular check-ups so liver health and growth can be monitored
• Tell schools, nurseries and carers about the condition and what foods to avoid

Medical treatments

Treatment is centred on diet, not on regular medicines. During a severe low blood sugar episode, healthcare professionals may give sugar in a form that reaches the blood quickly, such as through a drip in hospital, and will monitor the person closely. People with liver damage need specialist follow-up. Very rarely, when the liver is severely damaged, a liver transplant may be considered — this is a specialist decision and is not routine. Always speak to your own healthcare team before making any changes to treatment.

When is surgery considered?

Surgery does not treat or cure HFI. A liver transplant has been used in a very small number of people with severe liver damage, and only after specialist assessment. For almost everyone with HFI, the right diet is the treatment.

Living with this condition

Life with HFI means becoming an expert on what is in your food and drink. That sounds daunting at first, but most people settle into a routine within a few months with dietitian support. Fruit, fruit juice, honey, table sugar, high-fructose syrups and sorbitol-sweetened products are the main things to avoid, along with any processed foods that contain them. Many staples are safe, including starches, plain dairy foods, vegetables and grains, so meals can still be varied and enjoyable.

Lifestyle tips

• Build a list of safe meals and snacks you enjoy and keep it handy
• Ask restaurants and cafes about ingredients, and choose places that can answer clearly
• Keep an emergency plan that family, friends and work colleagues know about
• Wear or carry medical identification so emergency staff know about the condition
• Join a patient group or online community for practical tips and encouragement
• See your dietitian regularly, especially during pregnancy, growth spurts or illness

Diet and exercise

The diet is the heart of HFI care: avoid fructose, sucrose and sorbitol, and get enough energy from safe foods. A dietitian can help you build balanced meals that support normal growth in children and steady energy in adults. Exercise is good for overall health and is not limited by HFI, but it is worth planning snacks and hydration around activity, since hunger and low energy can feel similar to early low blood sugar. If you feel shaky or dizzy during or after exercise, stop, eat something safe, and seek advice.

Mental health and emotional wellbeing

Living with a rare condition can feel isolating, and food-based conditions can make social events, birthdays and meals out feel stressful. Children may feel left out, and parents often carry a lot of worry. These feelings are normal and very common. Talking to your dietitian, GP or a counsellor can help, and many people find real comfort in meeting others with the same condition. If you or your child ever feel overwhelmed or hopeless, please reach out for support straight away — contact your doctor, your local health service, or your local crisis line or emergency number if you need urgent help.

Prevention

HFI cannot be prevented, because it is written into your genes from the moment of conception. What can be prevented is harm from the condition: early diagnosis, a carefully planned diet and regular check-ups greatly reduce the chance of liver problems and low blood sugar episodes.

Vaccines

Vaccines do not treat or prevent HFI, but routine vaccinations are still recommended for general health. If you are worried about ingredients in any medicine or vaccine, ask your pharmacist or doctor to check for you.

Screening programmes

HFI is not included in routine newborn screening in most countries. Testing can be arranged if a baby or child has symptoms, or if a family member is known to have the condition. Genetic counselling can help families understand the chances of passing it on and what testing options exist before or during pregnancy.

Complications

If left untreated

• Repeated low blood sugar episodes, which can cause seizures and, rarely, lasting harm if severe
• Slow growth and poor weight gain in children
• Ongoing liver irritation that can, over many years, lead to scarring of the liver
• Kidney problems in some people with long-term, untreated disease
• Bleeding problems linked to liver damage
• Nutrition gaps if foods are cut out without dietitian support

Long-term outlook

The outlook for people with HFI who are diagnosed and supported is very good. Most people who follow their diet live full, healthy lives with normal growth, normal energy and normal life expectancy. Regular check-ups help catch any problems early, and dietitian support makes the diet easier to manage over time. If you have just been given this diagnosis, it is understandable to feel worried — but with the right team around you, this is a condition that can be lived with well.

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