Molybdenum Cofactor Deficiency
What else is it called?
- Combined Deficiency of Sulfite Oxidase, Xanthine Dehydrogenase, Aldehyde Oxidase and mitochondrial amidoxime reducing component (mARC)
- Combined Molybdoflavoprotein Enzyme Deficiency
- Combined Xanthine Oxidase and Sulfite Oxidase and Aldehyde Oxidase and mARC Deficiency
- Deficiency of Molybdenum Cofactor
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What causes it?
There are three forms of this disorder.
- Type A is caused by a problem in the MOCS1 gene
- Type B is caused by a problem in the MOCS2 gene
- Type C is caused by a problem in the GPHN gene
These genes are needed to produce different proteins which your body uses to make a molecule called molybdenum cofactor. This molecule is essential and enables certain enzymes (sulfite oxidase, xanthine oxidase and aldehyde dehydrogenase and mARC) to break down substances which would otherwise become toxic.
A problem in either of these genes means that the molybdenum cofactor molecule is missing due to an impaired synthesis of the cofactor itself or one of its precursors. This means that the enzymes which break down the substances do not work properly, and this allows chemicals to build up and become toxic. These chemicals include sulphite, S-sulfocysteine, xanthine and hypoxanthine. Sulfite is particularly toxic to the brain and high levels of this and the other chemicals cause the signs and symptoms of this condition.
How common is it?
We do not know exactly how common this condition is. It is believed to affect between 1 in 100,000 to 200,000 newborns worldwide, however it is thought that this condition is often misdiagnosed so numbers may be higher.
What are the signs and symptoms?
All the forms of this condition have the same signs and symptoms. Symptoms appear within a week of birth. Generally, the first symptoms include:
- Feeding difficulties
- Seizures which are unresponsive to treatment (intractable seizures)
This condition is characterised by progressive brain dysfunction and deterioration of the tissue in the brain. Symptoms may include:
- A severe delay or a failure to reach developmental milestones
- An exaggerated startle reaction to unexpected stimuli
- A small head size
- Coarse facial features, including a prominent forehead, sunken eyes, puffy cheeks, small nose, thick lips, and a long philtrum which is the indented part of the face underneath the nose and above the lips
- Dislocation of the lens in the eye
- Stiffness in the limbs making movements difficult
Prognosis is poor. Survival is not expected beyond early childhood.
A late onset form with a milder phenotype has also been described.
How is it diagnosed?
This disorder can be diagnosed by measuring the amount of sulfite, S-sulfocysteine, xanthine, hypoxanthine in the urine and low levels of a chemical called uric acid in the blood.
Diagnosis is confirmed by identification of genetic mutations in the 3 described genes through genetic testing. MRI scans can show the changes in the brain.
Can it be treated?
There is no cure for this condition. Treatment aims to provide relief for specific symptoms and ensure the highest possible quality of life is achieved. A team of specialists will be involved in the care and will provide support will be provided to your family.
A new treatment for type A has been developed and has shown some benefits including prevention of further damage to the brain, stopping seizures and it has also been reported to allow the child to reach developmental milestones. Gene therapy is also being explored as a future treatment.
Do my family need to be tested?
This is an inherited condition. Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes. We inherit particular 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.
Everyone has a pair of genes that are needed to make the molybdenum cofactor molecule. In children with this condition, neither of these genes works correctly. These children inherit one non-working gene from each parent.
Parents of children with this condition are known as carriers of the condition. Carriers do not have the disorder because the other gene of this pair is working correctly.
When both parents are carriers, in each pregnancy the risk to the baby is as follows:
- 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