ALG6-CDG

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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 in the ALG6 gene

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. ALG6-CDG is one of the most common types of CDG with just under 90 cases reported.

In most cases symptoms begin in infancy. Symptoms vary from case to case and also vary in severity. Symptoms that are characteristic of ALG6-CDG include:

• Low/weak muscle tone (hypotonia)
• A delay in reaching developmental milestones (developmental delay
• Epilepsy

ALG-CDG affects the hormones that coordinate sexual development and means that most females do not go through puberty.

Other symptoms that are common in this condition include:

• Problems with balance and coordinating movements (ataxia)
• Failure to grow or gain weight (failure to thrive)
• Speech problems or absent speech
• Muscle weakness
• Vision loss
• Behavioural problems including autistic behaviour, mood and temperament swings and sleep problems
• A low level of circulating blood cells (anaemia)

Protein-losing enteropathy can be life-threatening. This condition is 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. Symptoms linked to this condition include diarrhoea, an intolerance to food and fluid retention, both in general (oedema) and in the abdomen (ascites).

In rare cases, other symptoms of CDG may include:

• Shortened fingers and/or toes (brachydactyly)
• Crossing of the eyes (strabismus)
• Differences in the structure of the face
• A condition affecting the heart muscle that makes it harder for your heart to pump blood round your body (cardiomyopathy).
• Limb defects
• Abnormal fat distribution
• Blood clotting disorders, which may also include deep vein thrombosis
• A build-up of pressure around the brain, potentially causing chronic headaches, impaired vision, and poor quality of life (Idiopathic Intracranial Hypertension)                                                                                                                                                                                                   .

The prognosis of this condition varies, in most cases children live to reach puberty, and in some cases live into adulthood.

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.

Treatment is symptomatic and supportive and requires a multidisciplinary team of specialists. Management includes regular screening to measure the level of glucose in the blood, blood coagulation, and liver and endocrine function.

Supportive therapies include speech and language therapy, physiotherapy and occupational therapy. Dietary supplements are often given to help the child grow and gain weight. Tube feeding may be recommended to assist with feeding with a tube that is either passed through the stomach wall (gastrostomy) or through the nose into the stomach (naso-gastric tube feeding). Any dietary changes should only be implemented upon the recommendation and consultation of a specialist dietitian. An ophthalmologist may give eye patches or glasses to help vision and in some cases may recommend eye surgery to correct strabismus, if present. Seizures may occur and are treated with anticonvulsants; in rare cases patients may have seizures that do not respond to this treatment. Surgery may be required to treat some skeletal malformations that cause problems. Later in life, skeletal problems may require some mobility aids and orthopaedic management. Bleeding problems do not often cause major problems but special care and attention should be drawn to it if surgery is required; in these circumstances fresh frozen plasma is used.  Organs such as liver and heart will be regularly checked. In some CDG, certain medication(s) should be avoided; ask the advice of your specialist. It is important to attend follow-up appointments and attend check-ups with various specialists.

A special diet and in some cases further treatment may be provided should Protein Losing Enteropathy occur. Your specialist will advise on this.

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. ALG6-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). This is a general description of inheritance. For further information a genetic counselling service should be consulted.

CDG-UK

• Email: info@cdg-uk.org
• Website:https://cdg-uk.org/
• Facebook: https://www.facebook.com/UKCDG
• Instagram: https://www.instagram.com/cdg.uk
• Twitter: https://twitter.com/UK_CDG

• To raise awareness of this extremely rare disease and to reach out to other families who are affected by it. As more health professionals have become aware of CDG, more children and adults are being diagnosed in the UK, and as we know that a rare diagnosis can be isolating, and we wish to extend a hand of friendship to others facing the same.

• To raise funds for research into this group of currently untreatable diseases. According to Professor Jaak Jaeken, the first professional to identify CDG, ‘the rewards are many but the workers are few’. In other words, there is so much to be learnt about CDG and so much more that can be done in terms of diagnosis and possible therapies, but there are only a few researchers and doctors working in this area at the moment. With funding, we wish to change this by collaborating with researchers and health professionals with one end goal: a cure for CDG.

How we can help

References are available on request. Please contact us by phoning 0800 652 3181 or emailing contact@metabolicsupport.org [Resource Library No: ACDG03].

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This information about metabolic diseases is provided by Metabolic Support UK and is intended for educational purposes only. It should not be used for diagnostic or treatment purposes.

Should you require more detailed information please contact Metabolic Support UK by email (contact@metabolicsupport.org) or by telephone ( 0800 652 3181). For specific medical information regarding a disorder or individual please contact your GP or Paediatrician. Metabolic Support UK accepts no responsibility for any errors or omissions nor does Metabolic Support UK assume any liability of any kind for the content of any information contained within this summary or any use that you may make of it.