What else is it called?
- Congenital disorder of glycosylation type 1h
- Carbohydrate deficient glycoprotein syndrome type Ih
- CDG 1h
- CDG Ih
- CDG syndrome type Ih
- Congenital disorder of glycosylation, type 1h
- Congenital disorder of glycosylation type Ih
- Glucosyltransferase 2 deficiency
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What causes it?
The Congenital Disorders of Glycosylation (CDG) are a group of genetic disorders that have a broad spectrum of symptoms and range from mild to life-threatening in severity. This group is expanding at a rapid pace, and more than 60 different forms of CDG have been reported. Information about the disorders is always changing due to the developments in knowledge and new forms being reported.
The CDGs are caused by defects in one of the body’s natural processes called Glycosylation. This process uses hundreds of different enzymes to allow sugar molecules in the body to attach to certain proteins or lipids (fats). When this happens, they are given the names glycoproteins and glycolipids, respectively. Both are needed to carry out different tasks and are essential for the normal growth and function of the tissues and organs within the body. There are at least 100 steps, all using different enzymes, in the process of glycosylation. If one of the enzymes in the process does not function correctly it can cause a variety of symptoms, affecting many different parts of the body.
Previously, the CDGs were broken down into two groups known as CDG-I and CDG 2. However, more recently a new classification has been introduced and now all the CDG’s are listed with the abbreviation of the causative gene followed by “-CDG”. This type of CDG is caused by a fault on the ALG8 gene.
How common is it?
The exact incidence of CDG is unknown and it is believed that many cases go undiagnosed or are misdiagnosed as having other conditions. The number of cases is thought to rise significantly in the future with increase knowledge and understanding. ALG8-CDG has been reported in approximately 5 individuals.
What are the signs and symptoms?
ALG8-CDG is a multisystem disorder meaning that it can affect a number of organs, systems, and areas of the body.
In most cases symptoms begin at birth and babies may be born prematurely. Symptoms vary from case to case and vary in severity. Symptoms may include:
- Failure to grow or gain weight (failure to thrive)
- Protein-Losing Enteropathy; characterised by the loss of serum proteins from the digestive tract and leads to an abnormally low level of albumin and other proteins in the blood.
- Fluid retention, both in general (oedema) and in the abdomen (ascites)
- Problems with balance and coordinating movements (ataxia)
- Low/weak muscle tone, giving the appearance of babies being ‘floppy’.
- A delay in reaching developmental milestones (developmental delay)
- Vision problems, especially cataracts
- Differences in the structure of the face, including low set ears, widely spaced eyes, small teeth, misplaced jaw
- Club foot
- Shortened fingers and/or toes (brachydactyly) and crooked fifth finger (camptodactyly)
- Abnormal fat distribution
- Wrinkled skin and/or pale grey skin
- Inverted nipples
- An enlarged liver (hepatomegaly)
- Problems maintaining the body’s acid-base balance, blood pressure and the correct concentration of electrolytes in the body (renal tubulopathy)
- Blood clotting problems
- Structural brain abnormalities
- An accumulation of fluid in two or more areas of a foetus or newborn’s body (hydrops fetalis)
Prognosis is usually poor.
How is it diagnosed?
Diagnosis is based on the recognition of key symptoms, a detailed history and a clinical examination including specialised blood tests. Genetic testing can confirm the diagnosis.
Can it be treated?
Treatment is symptomatic and supportive and requires a multidisciplinary team of specialists involved in the care of your child and to support you and your family.
Do my family need to be tested?
Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes.
The word mutation means a change or error in the genetic instruction. We inherit particular chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents.
This is an inherited condition. There is nothing that could have been done to prevent your baby from having this condition.
We all carry two copies of each gene. ALG8-CDG is transmitted by an autosomal recessive mode of inheritance. A person who has one normal gene and one gene for the disease is termed a carrier for the disease and does not show any symptoms. The condition arises when an infant inherits a gene for the disease from both parents. The risk to the offspring of a couple who are both carriers is 25%. There is also a 25% chance that the child will not carry the abnormal gene. The risk of an unaffected sibling being a carrier is 2/3. Carriers do not show any symptoms (asymptomatic).