Fructose-1,6-bisphosphatase Deficiency

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This disorder is caused by a mutation (change) in the FBP1(9q22) gene which causes a lack of the enzyme fructose-1,6-bisphosphatase. The lack of this enzyme causes a decrease in the production of glucose (the main type of sugar in the blood). This means the body cannot properly make glucose which is the primary source of energy for the body.  

Fructose-1,6-bisphosphatase Deficiency is rare. Approximately 150 individuals have been affected worldwide to date. The prevalence in Italy is estimated at 1 in 147,575 people. In the Netherlands the prevalence is estimated at 1 in 350,000 and in France at less than 1 in 900,000.  

Symptoms for this disorder will vary from person to person and not all people with this disorder will have all these symptoms. These are some of the symptoms individuals with the disorder may have:  

• Metabolic acidosis (when the body produces too much acid)  
• Lactic acidosis (build up of lactate in the body)  
• Diarrhoea (watery stool)  
• Low blood sugar when fasting (Fasting Hypoglycaemia)  
• Vomiting  
• High blood uric acid level (Hyperuricemia)  

Less common symptoms include: 

• Drowsiness 
• Enlarged liver (hepatomegaly)  
• Intellectual (mental) deficiency  
• Breathing difficulties 
• Seizures  
• Irritability  
• Intermittent hyperventilation (intermittent over-breathing)  
• Low or weak muscle tone (Muscular hypotonia)  
• High liver enzymes (elevated hepatic transaminase)  
• Low blood sugar in newborn (neonatal hypoglycaemia)  
• Coma 

The disorder may occur in the newborn period with an enlarged liver (hepatomegaly), however, it usually occurs in infants of 2-4 months of age with symptoms including fast induced low blood sugars, metabolic acidosis (body producing too much acid), low blood sugars and episodes of apnoea (when a baby periodically stops breathing for a period longer than 15-20 seconds).   

These symptoms are usually brought on by fasting (for more than 8 to 10 hours), ingesting (eating) fructose, sorbitol or glycerol (types of sugars), or by vomiting, diarrhoea or infectious diseases.  

With proper treatment and management, FPB deficiency can have an excellent prognosis. However, this disorder can be fatal in the newborn period and during early infancy.  

The disorder can be diagnosed through specialised blood tests which will show blood sugar levels and levels of lactic acid in the blood. Enzyme activity can be measured in the white blood cells and the diagnosis will be confirmed through genetic testing of the FBP1 gene.  

Prenatal (before birth) diagnosis is possible through molecular analysis of amniocytes (cells of a foetus in the amniotic fluid).  

There is currently no newborn screening for this disorder in the UK.  

Treatment of this disorder focuses on avoiding hypoglycaemia (low blood sugars) and lactic acidosis (build up of lactate in the body). This is done through eating frequently and eating foods with high levels of glucose or maltodextrin. Any dietary changes require specialist dietitian’s advice and monitoring.  

Fasting periods any longer than 8 hours should be avoided, and episodes of infection should be carefully monitored. During acute (severe) episodes, fructose and sucrose should be avoided. Prevention and treatment of metabolic decompensation through consuming glucose orally (by mouth) or intravenously (by entering a vein with a needle) is essential (crucial).  

FBP deficiency is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.  

Carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with FBP deficiency are carriers.   

The pattern of inheritance in this condition is autosomal recessive. This means:   

When both parents are carriers, the risk to the baby in each pregnancy is  

• 25% chance (1 in 4) of developing the condition  
•  50% chance (1 in 2) for the baby to be a carrier of the condition  
•  25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier  

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: FCM004].