Crigler-Najjar Syndrome Type 2
What else is it called?
- Familial nonhemolytic unconjugated hyperbilirubinemia
- Hereditary unconjugated hyperbilirubinemia
- Bilirubin uridinediphosphate glucuronosyltransferase deficiency type 2
- Bilirubin-UGT deficiency type 2
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What causes it?
This disorder is caused by a problem with the UGT1A1 gene. This gene provides instructions for making the bilirubin-UGT enzyme which is responsible and necessary for the removal of bilirubin from the body. We can find the bilirubin-UGT enzyme primarily in livers.
If you have a problem in this gene, your body will have only less than 20 % of the normal bilirubin-UGT enzyme function. Therefore, your body will be unable to undertake a chemical reaction that turns the toxic form of bilirubin into a non-toxic form of bilirubin. This substance then builds up and becomes toxic and becomes toxic for the body. As result, it causes unconjugated hyperbilirubinemia and jaundice.
How common is it?
We do not know how many people have this disorder. It is very rare with only a small amount of cases that are known. However, it is estimated that 0,6 to 1 newborn in million would be affected. It can affect people from any race or background and affects males and females equally.
What are the signs and symptoms?
The signs and symptoms appear soon after birth or in early childhood and are mild or may be asymptomatic. Some cases may be detected only later in the life.
They are typically characterised by:
- Yellowing of the skin and whites of the eyes (jaundice)
- Chronic bilirubin encephalopathy (kernicterus):
- Extreme tiredness (lethargy)
- Weak muscle tone (hypotonia)
- Episodes of increased muscle tone (hypertonia)
- Episodes of arching of the back
- Neurological problems-
- Involuntary writhing movements of the body (choreoathetosis)
- Acute bilirubin encephalopathy – only if chronic bilirubin encephalopathy is not present:
- Mild to moderate muscle tone (hypotonia)
- High pitched cry
- Extreme tiredness (lethargy)
- Poor suck
- Patterned, repetitive muscle contractions that result in neck extension (retrocollis)
- Dramatic abnormal posture due to spastic contraction of the extensor muscles of the neck, trunk, and lower extremities (opisthotonos)
- Semi-comatose or comatose state
- Enlarged liver and spleen (hepatosplenomegaly)
Due to the high severity, the prognosis is poor. Affected children can die in childhood. Although, proper treatment may prolong their survival. Emergent treatment during the hyperbilirubinemia crisis may be required. Most patients survive into puberty without any serious brain damage but eventually develop chronic bilirubin encephalopathy. The development of chronic bilirubin encephalopathy may be irreversible.
How is it diagnosed?
You will be diagnosed after a clinical examination by your specialist or doctor. However, as the signs and symptoms of this disorder are similar to other conditions, you will need further tests. Doctors will analyse your blood using a special test called the bilirubin blood test. The diagnosis is confirmed by the DNA test.
Can it be treated?
This is a progressive disorder and the only available curative treatment is liver transplantation. Therefore, treatment is focused on managing individual symptoms and providing comfort and relief in the form of supporting the individual and any family members. A multi-disciplinary team of specialists and support networks will be involved in the management of the condition and to offer practical and emotional support.
One of the two most used treatment methods is phototherapy, which is the most effective in the early years and losing its effectiveness in older children and adults. The second is plasmapheresis. You may also be prescribed an orlistat, calcium phosphate supplementation, bilirubin production inhibitor, and phenobarbitol. Gene therapy may also be considered. Hepatocyte transplantation may be considered an alternative to liver transplantation.
Do my family need to be tested?
Crigler-Najjar syndrome type 2 can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.
If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.
If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.
Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited Crigler-Najjar syndrome type 2. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.
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