Glycerol Kinase Deficiency

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Glycerol Kinase Deficiency occurs when the glycerol kinase gene which is found on the locus Xp21 of the X chromosome, is deleted or mutated (changed).  

When someone suffers from glycerol kinase deficiency, many of the glycerol molecules that are released into the bloodstream do not get converted to DHAP (dihydroxyacetone phosphate) like they should be because there is not enough of the enzyme to catalyse (cause or accelerate a reaction) all the reactions that are meant to occur. This results in the extra molecules of glycerol left floating around in the cell which can cause serious damage when left untreated.  

GKD is a rare genetic disorder. It is known the affect less than 200,000 individuals in the United States.  

There are three distinct forms of this deficiency: Infantile (babies or very young children), juvenile (adolescent/ teenager) and adult.  

 The symptoms that are present at birth or shortly after include: 

• Cryptorchidism (the absence of one or both testes from the scrotum) 
• Strabismus (cross-eyed) 
• Seizures 

Other symptoms become more noticeable with time. Vomiting and lethargy are usually the only symptoms, if any, that are present in adults with GKD. Adults with GKD tend to have fewer symptoms than infantile or juvenile GKD.  

Very frequent symptoms for infantile or juvenile GKD: 

•  Adrenocortical hypoplasia (small adrenal cortex- the outer part of the gland)  
• EMG abnormality (abnormal results from tests using electromyography, used to record the electrical activity produced by skeletal muscles) 
• Elevated serum creatine phosphokinase (an increase in the level of the creatine kinase enzyme in the blood) 
• Global developmental delay (delay in motor or mental milestones- motor skills, speech, language, cognitive skills, social and emotional skills. This is in children younger than five years)   
• Intellectual disability (defined as an IQ score below 70)  
• Metabolic acidosis (overproduction of acid in the body)  
• Muscular hypotonia (decreased muscle tone) 
• Myopathy (muscular weakness) 
• Neurological speech impairment  
• Reduced tendon reflexes  
• Short stature (individuals with a height considerately below average)  

 Frequent symptoms for infantile or juvenile GKD:  

•  Cryptorchidism (the absence of one or both testes from the scrotum)  
• EEG abnormality (abnormal results from an electroencephalogram, used to track electrical activity of the brain) 
• Hyperlordosis (C-shaped curve in the lower back)  
• Osteoporosis (a medical condition in which bones become brittle and fragile)  
• Scoliosis (abnormal sideways curve of the spine)  
• Seizures  

GKD is diagnosed through specialised blood and urine tests to find the amount of glycerol present. To confirm the diagnosis of infantile GKD, genetic testing of the Xp21 gene can be done. Juvenile and adult GKD patients often have no symptoms and are diagnosed by chance when tested for another medical condition.  

Treatment for GKD is aimed at treating the symptoms because there is no permanent treatment. The main treatments used include corticosteroids (steroid hormones) which control stress responses, carbohydrate metabolism (absorption) and blood electrolyte levels.  

A glucose infusion is also used together with an insulin infusion to check blood glucose levels and keep them stable. Other steroid hormones that are used are mineralocorticoids which control electrolyte levels and allow the kidneys to keep hold of sodium.

Glycerol Kinase Deficiency 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 in this condition is X-inked recessive. This means that the gene causing the trait of the disorder is located on the X chromosome. Females have two X chromosomes and males have one X and one Y chromosome. Carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with GKD are carriers. 

References are available on request. Please contact us by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [GCM013].