Glycogen Storage Disease Type 1B
What else is it called?
- G6PT deficiency
- Glucose-6-phosphate transport defect
- Von Gierke disease
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What causes it?
GSD1B is caused by problems with the SLC37A4 gene. The SLC37A4 gene provides instructions for making a protein called glucose 6-phosphate trans close. Problems in these genes prevent the breakdown of the complex sugar (Glucose 6-phosphate) and as a result the complex sugar gets converted into glycogen and fat which is stored within cells. Too much glycogen within a cell can be toxic and build up can damage organs and tissues throughout your body, including the liver and kidneys. These issues eventually lead to the signs and symptoms of GSD 1B outlined below.
People with GSD 1B have a shortage of white blood cells in their bodies and this can make them prone to recurrent bacterial infections. This shortage of white blood cells is usually apparent by age 1.
How common is it?
The overall incidence of GSDI is 1 in 100,000 individuals
What are the signs and symptoms?
Signs and symptoms may include:
- Recurrent bacterial infections
- Inflammation of the intestinal walls (IBS)
- Oral problems – cavities, inflammation of the gums, chronic gum disease, abnormal tooth development, ulcers I the mouth.
- Low blood sugar levels
- Build of lactic acid in the body
- High levels of uric acid
- Excess amounts of fats in the blood
- Thin arms and legs and short stature
- Enlarged liver and/or kidneys
- Delayed puberty
- Thinning of bones. / arthritis
- Kidney disease
- High blood pressure in the blood vessels that supply lungs
- Polycystic Ovaries (females only)
- Liver adenomas
How is it diagnosed?
GSD Type 1B is diagnosed via laboratory tests which look for abnormal levels of glucose, lactate, uric acid, triglycerides and cholesterol. Testing for the G6PC and SLC37A4 gene’s is also preformed to confirm diagnosis. This test can also be used to test whether a patient or family member is a carrier and for prenatal diagnosis.
Making a diagnosis for a genetic or rare disease is often challenging. Healthcare professionals will usually look at your medical history, symptoms, perform a physical examination and review laboratory tests results before making a diagnosis.
If you have any concerns or suspect you may have GSD Type 1B, you should speak to your GP in the first instance. If your GP suspects you may have GSD 1B they will refer you for further testing. If you have received a diagnosis of GSD 1B, you will be referred to specialist metabolic consultant and team.
Can it be treated?
Patients with GSD 1B will be referred to specialist dietician who will provide a specialist diet which maintains normal glucose levels and prevents low blood sugar levels. Diets will vary per patient but generally frequent servings of carbohydrates during the day must be maintained and calcium, vitamin D and iron supplements may be recommended. A specialist consultant or nurse may prescribe medicines to lower lipid levels and prevent and/or treat kidney disease. GSD 1B patients found to have liver adenomas may be treated with surgery.
Patients with GSD1B should be monitored annually by liver and kidney ultrasounds and frequent blood tests. If you or someone you know has been affected by GSD 1B you may want to consider genetic counselling, you will need to speak to your GP or metabolic specialist for a referral to a genetic counsellor.
Do my family need to be tested?
Glycogen Storage Disease Type 1 is inherited via an autosomal recessive inheritance pattern. 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.
The pattern of inheritance of glycogen storage disease type 1B is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with glycogen storage disease type XI are carriers.
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
Genetic counselling can be requested to get a full explanation.
Carrier testing can be offered to adult relatives of affected patients once a disease-causing mutation has been identified.
For more information, please visit Association for Glycogen Storage Disease UK.