Glycogen is a molecule used by the body to store carbohydrate energy that can be used as needed. A deficiency of the debrancher enzyme can interfere with this process.
Glucosidase aids in carbohydrate absorption, whilst transferase refers to enzymes that move functional groups from one molecule to another or from the donor to the acceptor. Those with Glycogen storage disease type III have problems with both.
Individuals with Glycogen storage disease type III have either types IIIa, IIIb, IIIc, or IIId. Type a lack both glucosidase and transferase in the liver and muscles. Individuals with b lack both but, in the liver, only. Sufferers with c have a loss of glucosidase activity in the body, and d sufferers have no transferase activity.
Glycogen storage disease type III symptoms usually occur during infancy with symptoms such as hypoglycaemia, which is low blood sugar. This can lead to dizziness, confusion, irritability, sweating, and a rapid heartbeat. Even fainting is possible if blood sugars become dangerously low.
Infants with this enzyme deficiency can be underweight, weak, and have slow physical growth. Liver enlargement can also be present, whilst heart disease and loss of muscle tone can also occur. Some of these symptoms can begin to regress during the early to mid-teens.
A debranching enzyme helps to break down glycogen and store it as glucose in the body through glucosyltransferase and glucosidase activity. Debranching enzymes use glucose reserves from glycogen deposits in the muscles and liver. This acts as a storage of energy reserves.
The breakdown of glycogen mainly takes place in the liver with the aid of the hormone’s glucagon and insulin, and this creates a balanced blood glucose level.
However, a deficiency in the debrancher enzyme and, more especially, the glycogen debranching enzyme amylo-1,6-glucosidase, 4r-alphaglucanotransferase can lead to Glycogen storage disease type III. Here, glycogen is not broken down and used as a carbohydrate energy reserve. Instead, glycogen deposits build in the liver, muscles, and even the heart.
It is an autosomal recessive disorder which means that two copies of the mutated gene responsible for creating the deficiency must be passed down, one from each parent, to place an infant at risk of suffering from this condition.
A physical examination is usually the best starting point in diagnosing a debrancher enzyme deficiency disease such as Glycogen storage disease type III. If such a condition is suspected from the symptoms presented, then a muscle or liver biopsy can be taken for close examination.
A blood test can also help detect enzyme levels, and an ultrasound scan can check for liver enlargement and disease noninvasively.
Treatment includes a high-protein diet in order to facilitate gluconeogenesis in the body. Vitamin D can help prevent bone problems which can be a complication of this illness. A liver transplant may be needed if the liver has sustained severe damage from this disease.
Prevention is mostly through genetic screening of those thinking of starting a family. If they are both carriers of the gene mutation, then not having any children together would prevent infants from being born with this deficiency.