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What

Fructose 1,6-Diphosphatase (FDPase) deficiency is a rare and inherited condition where the body is not able to break down fructose in the diet. FDPase is characterized by hypoglycemia, or low blood sugar, during periods of fasting. Fructose is the sugar found in fruits and is made up of glucose, a simple sugar. The body normally uses glucose as its main source of energy. During fasting, blood glucose levels must be maintained at adequate levels in order for the body to continue to function. Initially, glucose stored in muscle and the liver is used. After the glucose in the liver and muscle is used up proteins in the body are broken down and converted into glucose. FDPase is involved in this process.

Who

Approximately 1 out of every 20,000 children have FDPase deficiency. Girls and boys of all races and ethnicities are affected equally.

Signs and Symptoms

Symptoms of hypoglycemia typically present during the newborn period. Episodes can be triggered by foods that contain fructose and also by infant formulas. Later episodes in childhood are often triggered by fasting, vomiting and fever. Hypoglycemia can present in the form of irritability, dizziness, lethargy, seizures, fainting, trembling, and confusion. The liver may become enlarged during an episode, but usually returns to normal size with treatment.

Possible Causes

FDPase deficiency is inherited in an autosomal recessive manner. This means that two genes with a change, or mutation, are necessary to have this disorder. The parents of the affected child are usually healthy, but each carries a copy of the mutated gene. When both parents are carriers, there is a 25% chance that each of their children will develop this disease. FDPase deficiency is not contagious or preventable. FDPase deficiency is caused by a change in a specific gene located on chromosome 9. This gene normally makes the FDPase protein, which is found in the liver. FDPase is needed to form glucose from proteins during periods of fasting. When FDPase is absent and fructose is ingested, glucose production is prevented and lactic acid, a toxic waste product, builds up.

Diagnosis

FDPase deficiency can be diagnosed with a fructose challenge test. Children are given fructose during a period of fasting and their blood glucose levels and lactate levels are monitored. Glucose levels will be low and lactate levels will be high in affected individuals. This test can be dangerous and close monitoring is important. The preferred diagnostic test is needle biopsy of the liver to measure FDPase activity. This test requires that a needle be inserted into the abdomen to retrieve a small piece of liver tissue.

Treatment

FDPase deficiency can be diagnosed with a fructose challenge test. Children are given fructose during a period of fasting and their blood glucose levels and lactate levels are monitored. Glucose levels will be low and lactate levels will be high in affected individuals. This test can be dangerous and close monitoring is important. The preferred diagnostic test is needle biopsy of the liver to measure FDPase activity. This test requires that a needle be inserted into the abdomen to retrieve a small piece of liver tissue.

Prognosis

Hypoglycemia and lactic acidosis are toxic to the brain, liver and kidneys. Episodes in the newborn infant are often lethal. With early diagnosis, prognosis is very good. Later in childhood, tolerance to fasting improves.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Organic Acidemia Association http://www.oaanews.org Voluntary support group which represents children and adults with these disorders, their families and caregivers. CLIMB (Children Living with Inherited Metabolic Diseases) http://www.CLIMB.org.uk National organization providing information, news, financial support and networking. NIH/National Institute of Diabetes, Digestive and Kidney Diseases Endocrine Diseases Metabolic Diseases Branch http://www.niddk.nih.gov National organization providing information, support, and newsletters.

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References and Sources

www.emedicine.com/ped/topic806.htm www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=229700 www.diseasesdatabase.com/umlsdef.asp?glngUserChoice=5012