Fanconi-Bickel syndrome (FBS) is a rare inherited disorder of carbohydrate metabolism caused by mutations in the gene known as GLUT2.
Description
Also known as glycogen storage disease type XI, the disease was first described by scientists G. Fanconi and Horst Bickel in 1949. Since then, only a few dozen cases of FBS have been studied, most in the United States, Europe, and Japan.
Onset of FBS is within the first year of life, with the overt symptom being a failure to thrive. At age two, an
enlarged liver and kidneys are present and the child has rickets. The incidence of FBS has not been determined but it is believed to occur in less than one in one million births.
Genetic profile
FBS is believed to be an autosomal recessive disorder. This means that an individual with FBS would have to inherit an abnormal copy of the gene from both parents in order to show symptoms of FBS. People with only one abnormal gene are carriers and do not have the disorder. When both parents have the abnormal gene, there is a 25% chance with each birth that their child will inherit both abnormal genes and have the disease. There is a 50% chance each birth that the child will inherit one abnormal gene and become a carrier of the disorder but not have the disease itself. There is a 25% chance each child will inherit neither abnormal gene and not have the disease nor be a carrier. The specific genetic defect of FBS has not been identified.
Demographics
Since there is so little research on Fanconi-Bickel syndrome, no clear pattern of demographics has been established. However, the disorder is known to affect both males and females. One common thread in some of the cases that have been studied has been consanguinity, meaning that FBS is found in the children of two persons of the same blood relation. In several of these cases the consanguinity is between two first cousins.
Signs and symptoms
In a 1987 study by researchers at the Research Institute for Child Nutrition in Dortmund, Germany, nine cases of Fanconi-Bickel syndrome were compared for clinical symptoms, behavior symptoms, and physical appearance. The initial symptoms reported were fever, vomiting, growth failure, and rickets between the ages of three and ten months. Later, these same patients showed signs of dwarfism, a protruding abdomen, enlarged liver, moon-shaped face, and abnormal fat deposits around the shoulders and abdomen. Also, cutting of teeth and puberty were delayed. Complications present included fractures and pancreatitis (an enlarged pancreas). Later in life, rickets and osteoporosis were constant features.
The German study, whose researchers included H. Bickel, co-discoverer of the syndrome, also used ultrasound to determine increased kidney size and growth in relation to body height. The most prominent finding was glucosuria (glucose, or sugar, in the urine). Polyuria (increased urination) was also a constant finding. The study noted that liver size was normal or slightly increased at birth in all nine cases but became greatly enlarged during infancy. The liver size and glycogen (a glucose storage molecule) content were reduced when the patients were placed on an antiketogenic (high carbohydrate) diet.
Other laboratory findings included fasting hypoglycemia (low levels of sugar in the blood), ketonuria (high levels of ketones in the urine), high hypercholesterolemia (high cholesterol), hypophosphatemia (high phosphate levels in the blood), and high levels of amino acids and protein in the urine. In a 1995 study at Children's Hospital in Philadelphia of an eight-year-old with Fanconi-Bickel syndrome, doctors reported additional symptoms of overworked kidneys, very small amounts of albumin (a class of water soluble proteins) in the urine, and an increase in the number of cells in the inner part of the kidney that filters blood.
Diagnosis
Fanconi-Bickel syndrome can usually be identified in patients by neonatal screening for galactose, a type of sugar. Patients with FBS are intolerant to galactose. Other diagnostic factors include an impaired glucose tolerance test, x ray to determine the pattern of rickets, urine tests to measure levels of glycose, phosphates, amino acids, and bicarbonate, and a liver biopsy to detect abnormal galactose oxidation.
Treatment and management
There is no effective treatment for Fanconi-Bickel syndrome. However, some of the symptoms can be treated with adequate supplementation of water, electrolytes, and vitamin D, restriction of galactose, and a diabetes mellitus-like diet (low sugar and low carbohydrate) presented in frequent small meals. These treatments can improve growth and give the patient a general sense of well-being.
Prognosis
The long-term prognosis has not been determined. It may depend on the severity of symptoms and early diagnosis and treatment of symptoms. The first person diagnosed with the disorder in 1949 was a four-year-old Swiss boy with consanguineous parents. At six months, the boy had excessive thirst, constipation, and was not thriving. He was treated with vitamin D and calcium supplements. At about age four, the boy had short stature, a protruding abdomen, an enlarged liver, facial obesity, osteopenia, and hyperlordosis. At age 12, the boy was found to be resistant to glycogen. In 1997 at age 52, the patient, without any treatment other than vitamin D and calcium supplements, was of short stature (4 ft 8 in or 140 cm tall), weighed about 95 lbs (43 kg), had a moderately protruding abdomen, and a smaller than normal liver. Other than arthritis, he had no medical complaints. However, other people diagnosed as children with FBS had much shorter life spans. Long-term follow-up studies of nine persons with FBS showed severely retarded growth, partly compensated for by late onset of puberty.
Muller, D., et al. "Fanconi-Bickel Syndrome Presenting in Neonatal Screening for Galactosaemia." Journal of Inherited Metabolic Disease (August 1997): 20-24.
Sahin, Figen, et al. "Glycogen Storage Disease with Renal Tubular Dysfunction (Type XI, Fanconi-Bickel Syndrome)." Archives of Pediatrics and Adolescent Medicine (November 2000): 1165.
ORGANIZATIONS
American Association of Kidney Patients. 100 S. Ashley Dr., Suite 280, Tampa, FL 33602. (800) 749-2257. <http://www.aakp.org>.
National Kidney Foundation. 30 East 33rd St., New York, NY 10016. (800) 622-9010. <http://www.kidney.org>.
National Organization for Rare Disorders (NORD). PO Box 8923, New Fairfield, CT 06812. (203) 746-6518 or (800) 999-6673. Fax: (203) 746-6481. <http://www.rarediseases.org>.
WEBSITES
"Fanconi-Bickel Syndrome; FBS." (Entry No. 227810). National Center for Biotechnology Information, Online Mendelian Inheritance in Man (OMIM).<http://www3.ncbi.nlm.nih.gov/>.
