Glycogen Storage Disease Type XIV

What else is it called?

  • GSD type 14 
  • GSDXIV 
  • PGM1-CDG 
  • Phosphoglucomutase deficiency type 1 
  • Type 14 glycogenosis 
  • Congenital disorder of glycosylation, type It  
  • CDG syndrome type It 
  • CDG-It 
  • CDG1T 
  • Congenital disorder of glycosylation type 1t 
  • Congenital disorder of glycosylation type It 
  • Phosphoglucomutase-1 deficiency 
  • PGM1-related congenital disorder of glycosylation 
  • Glycogen storage disease due to phosphoglucomutase deficiency 

Get in touch

Contact our caring team on 08452 412 173 for help and support. Our phone lines open 10am-4pm, Monday to Friday.

Prefer to email? Our email address is contact@metabolicsupportuk.org.

What causes it?

GSD type 14 is caused by mutations (changes) in the PGM1 gene which encodes (converts) for the enzyme, Phosphoglucomutase 1. This enzyme moves phosphate groups back and forth on glucose (sugar) molecules. When there are mutations in the PGM1 gene, abnormal concentrations of activated sugars (sugars and phosphate structures) build up in the cells and shuts down protein glycosylation (the process by which a carbohydrate is attached to a target protein). A lack of the PGM1 enzyme also makes it difficult for GSD type 14 patients to breakdown glycogen (the stored form of sugar) in their cells.

How common is it?

GSD type 14 is a rare inherited condition. The exact prevalence is unknown, but it is estimated to affect less than 1 in 1,000,000 people. 

What are the signs and symptoms?

The signs and symptoms for GSD type 14 vary from patient to patient and not all individuals with the condition will have all the symptoms listed below. Symptoms may include:  

5-29% of patients have these symptoms:  

  • Cerebral venous thrombosis (blood clot in the cerebral vein)  
  • Cleft palate (cleft roof of mouth)  
  • Dyspnea (trouble breathing/shortness of breath)  
  • Elevated serum creatine kinase (raised levels of blood creatine phosphokinase)  
  • Fatigue (tiredness) 
  • Pierre-Robin sequence (a set of abnormalities affecting the head and face including): 
    • Micrognathia (small lower jaw) 
    • Glossoptosis (a tongue that is placed further back than normal)  
    • Blockage/obstruction of the airways 
  • Rhabdomyolysis (breakdown of skeletal muscle)  

Other symptoms include (the % of patients with these symptoms is unknown): 

  • Bifid uvula (cleft in the uvula – the fleshy extension at the back of the soft palate which hangs above the throat) 
  • Delayed puberty  
  • Dilated cardiomyopathy (stretched and thinned heart muscle)  
  • Elevated hepatic transaminase (high liver enzymes)  
  • Exercise intolerance (decreased ability to exercise)  
  • Hepatic steatosis (fatty liver) 
  • Hepatitis (liver inflammation/swelling)  
  • Hypoglycaemia (low blood sugar)  
  • Muscle weakness  
  • Short stature (body height lower than average)  
  • Tachycardia (fast heart rate)

How is it diagnosed?

GSD type 14 can be diagnosed through specialised blood tests and liver function tests. A diagnosis can be confirmed through molecular genetic testing which will show mutations in the PGM1 gene.  

Can it be treated?

There is currently no cure available for GSD type 14, however, the condition can be detected at an early stage to provide proper care and counselling. 

Treatment for this condition is mainly symptomatic and supportive. This aims to manage and alleviate individual symptoms and to provide support for the patients and their families. One of the treatments includes frequent feedings and a complex carbohydrate diet. Please note that any dietary changes require specialist dietitian’s advice and monitoring. 

Do my family need to be tested?

GSD type 14 is an inherited condition. 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 GSD type 14 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 GSD type 14 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.  

 

Relevant Organisations

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing helen@metabolicsupportuk.org [Resource Library No: AAP002]. 

References

For more information, please visit Association for Glycogen Storage Disease UK.

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