Fanconi-Bickel Syndrome

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This condition is caused by a fault in the SLC2A2 gene. This gene is needed to enable our body to make a protein called Glucose-transporter protein 2 (also known as GLUT2). We need GLUT2 to allow us to transport glucose through our body.

Glucose comes from the food we eat. Our body breaks down carbohydrates and converts them into glucose (sugar) so our body can use it as the main source of energy for the cells. When we do not need the glucose, our body converts it into glycogen so it can be stored. When we need the energy, our body can then convert the glycogen back into glucose so the body can use it.

A fault in the SLC2A2 gene means that the GLUT2 protein cannot function properly. As a result, you will be unable to transport glucose efficiently and the glycogen will build up in the liver and kidneys which cause the signs and symptoms of this condition.

We do not know exactly how many people have this condition worldwide. It is believed that there are less than 200 cases worldwide. There is a higher incidence in the Middle East and is more prevalent in consanguineous families (blood relations).

Signs and symptoms often begin during infancy between 3 and 10 months of age and initial symptoms may include:

• Severe diarrhoea
• Vomiting
• Excessive production of urine (polyuria)
• Failure to grow or gain weight at the expected rate
• Hypophosphataemic rickets (characterised by bone pain and soft, weak bones that bend easily due to a lack of phosphate in the blood)

Symptoms are variable, even amongst members of the same family. Other symptoms include:

• Low blood sugar (hypoglycaemia) after long periods without food
• Low levels of insulin (hypoinsulinaemia)
• Enlarged liver and spleen (hepatosplenomegaly) causing a swollen abdomen
• Poor appetite
• Delays in reaching developmental milestones
• Delayed puberty
• Osteoporosis
• Uneven fat distribution

Diagnosis is based on a clinical examination and a range of specialised blood and urine tests. Tests reveal:

• Excessive glucose in the urine (glucosuria)
• High levels of protein in the urine (proteinuria)
• High levels of phosphate in the urine (phosphaturia)
• Low levels of phosphate in the blood (hypophosphatemia)
• High levels of acid in the blood and urine
• Low blood sugar (hypoglycaemia)
• Ketones in the urine
• High blood cholesterol level
• High levels of biotinidase in the blood

A liver biopsy may be performed to reveal the accumulation of glycogen. Diagnosis can be confirmed by genetic testing.In some countries, this condition may be detected through neonatal screening for another metabolic disorder called Galactosaemia. This is not currently available in the UK.

There is no cure for this condition. Treatment is aimed at providing relief for the symptoms and to provide support for you and your family. You will have a team of specialists to help you to manage this condition including a specialist dietitian. Treatment includes a low-galactose diabetic diet which focuses on using fructose as the main carbohydrate. Vitamin D and phosphate supplements can help to prevent rickets.

With early diagnosis and correct treatment, the prognosis is very good and can improve growth and cognitive function. Later diagnosis and management can improve some symptoms but generally the earlier this condition is detected, the better the outcome. If this condition is left undiagnosed and untreated it can lead to liver failure and can become life-threatening.

This condition can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.

If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited this condition. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: FCM011].