What is Forbes Disease?
Forbes Disease belongs to the family of glycogen storage disorders and is inherited as an autosomal recessive disorder. The main cause of the symptoms of Forbes Disease is a deficiency of an enzyme called debrancher enzyme. As a result of deficiency of this enzyme, there is excess glycogen accumulated in the liver, some muscles of the body and in some cases even the heart.
Forbes Disease is basically of two types, the first type is GSD IIIA which is responsible for about 90% of cases of Forbes Disease and affects the liver as well as the muscles. The remaining 10% have GSD-IIIB form in which only the liver is affected due to abnormal accumulation of glycogen as a result of Forbes Disease.
What are the Causes of Forbes Disease?
The root cause for Forbes Disease is a fault in the gene which has been traced to the chromosome 1p21. Forbes Disease is inherited as an autosomal recessive trait meaning that two copies of the faulty gene one from each parent is required for the development of this condition. This results in deficiency of the debrancher enzyme, the function of which is the formation of glycogen. Glycogen is used up in the body for energy purposes. The carbohydrates that we eat, break down into glycogen and stored in the liver from where it breaks down into sugar which provides energy.
In cases of Forbes Disease, due to the deficiency in the debrancher enzyme, the glycogen is not able to break down completely and some part of the glycogen starts accumulating in the liver and other muscles of the body. This ultimately results in the symptoms that are classic for Forbes Disease.
What are the Symptoms of Forbes Disease?
The classic presenting features of Forbes Disease may not be apparent till the child is around six years of age and resemble that of other glycogen storage disorders. The main features of Forbes Disease include hepatomegaly and abnormal protrusion of the abdomen.
There is flaccidity of the muscles of the body as well due to Forbes Disease. Some of the other features of this condition are short stature, hypoglycemia which does not resolve even with hormone replacement of glucagon.
There is also accumulation of fatty substances in the body leading to hyperlipidemia. Children with Forbes Disease have a compromised immune system and have a tough time fighting off infections.
In some cases a child with Forbes Disease may be completely asymptomatic other than hepatomegaly and perhaps a protruded abdomen and these symptoms also fade away as the child grows and goes into his or her teens. Children with Forbes Disease also may have a delay in attaining puberty as a result of Forbes Disease.
How is Forbes Disease Diagnosed?
To diagnose Forbes Disease, a battery of specialized testing may be required to include a liver function test which will show increased levels of glycogen a muscle biopsy may also show abnormal glycogen present which points to a glycogen storage disorder. Genetic testing may show the deficiency in the debrancher enzyme and the faulty gene responsible for this condition thus confirms the diagnosis of Forbes Disease.
How is Forbes Disease Treated?
The front line treatment for Forbes Disease is administration of intravenous glucose on a continuous basis to prevent hypoglycemia. Small meals containing some amount of carbohydrates and high in proteins is given to the patient during the day. For nights, administration of glucose on a continuous basis is given to promote normal growth of the child which tends to get affected due to Forbes Disease.
Forbes Disease does not have any effect on the life expectancy of an individual although in some cases there have been certain muscle disorders noted in individuals with Forbes Disease.