Mitochondrial respiratory chain complex I deficiency

What else is it called?

Mitochondrial respiratory chain complex I deficiency (MRCID) is also known as: 

  • Isolated NADH-CoQ reductase deficiency  
  • Isolated NADH-Coenzyme q reductase deficiency  
  • Isolated NADH-ubiquinone reductase deficiency  
  • Isolated mitochondrial respiratory chain complex I deficiency  
  • NADH:Q(1) oxidoreductase deficiency  

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What causes it?

MRCID is caused by a problem in the nuclear of mitochondrial genes, which causes the protein called complex I to be made in short supply or incorrectly. By having a problem in this nuclear or mitochondrial gene the cells within the body will have a hard time converting food into energy. 

How common is it?

Mitochondrial diseases are thought to occur in about 1:8,500 people and this form of the disorder is the most common cause of mitochondrial disease in children. it accounts for around 30% of cases. 

What are the signs and symptoms?

MRCID can manifest at any age and the signs and symptoms are: 

  • Decreased activity of Complex I 
  • Loss of control of bodily movements (ataxia) 
  • Failure to thrive  
  • Enlarged liver (hepatomegaly)  
  • Hypoglycaemia  
  • Enlarged and thickened heart muscle (hypertrophic cardiomyopathy)  
  • Increase lactate in the body (lactic acidosis)  
  • Lethargic 
  • Weak muscle tone 
  • Cross eyed (strabismus) 
  • Respiratory impairment  
  • Involuntary rapid eye movements 

How is it diagnosed?

MRCID can be diagnosed using a person’s genetic medical history, their symptoms, a physical examination and take samples of their blood and urine in order to make an accurate diagnosis. 

Can it be treated?

There is an orphan drug known as alpha-tocotrienol quinone available in both Europe and the USA. However, it is used to treat leigh syndrome, which is a disorder related to MRCID.  

Do my family need to be tested?

MCID is an autosomal recessive inherited metabolic disorder which means that for a person to inherit this disorder, they will need to inherit it from their parents. Humans are made up of 46 chromosomes and we inherit 23 chromosomes from each parent, in the form of the egg and sperm which combine to determine the characteristics of the child. Every human being has two copies of the genes which are needed in order to produce the complex I protein. If both of these genes are faulty then MCID will develop. The parents do not necessarily need to suffer from MCID they can be carriers, carriers are people who carry one faulty gene for a particular protein and they do not develop the disease because the other gene works correctly.  

In the event that both of the parents are carriers of MCID. There is a: 

  • 25% chance that one of the children will be unaffected by MCID and will not be a carrier. 
  • 25% chance that the child will inherit MCID.  
  • 50% chance that the child will be unaffected by MCID and will be a carrier.     

Relevant Organisations


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

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