What else is it called?
- Combined prosaposin deficiency
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What causes it?
Prosaposin deficiency is caused by mutations (changes) in the PSAP gene which cause the absence or not functioning of the prosaposin protein. It is not well understood what the exact function of this protein is.
Normally, the processing of prosaposin produces four smaller proteins called Saposins (Sap) A, B, C and D. When there is a deficiency in just one of these proteins, it results in a rare genetic form of Krabbe disease (Sap A), metachromatic leukodystrophy (Sap B), Gaucher disease (Sap C) and Farber disease (Sap D). In prosaposin deficiency, the is a combined deficiency of all four proteins.
How common is it?
Prosaposin deficiency is very rare, with a prevalence of less than 1 in 1,000,000 people. Less than 10 cases have been reported so far.
What are the signs and symptoms?
Symptoms usually show immediately after birth and most individuals with this condition do not survive past the age of 4 months. Signs and symptoms of this condition include:
- Hypotonia (decreased muscle tone)
- Massive myoclonic bursts (sudden, brief, shock-like jerks)
- Abnormal ocular movements (rapid movement of one or both eyes)
- Dystonia (a movement disorder where muscles contract uncontrollable)
- Hepatosplenomegaly (enlarged liver and spleen)
- Pulmonary infection (lung infection)
The deaths of the patients that have been reported were between 1 and 4 months old and usually occurred from respiratory failure due to repeated pulmonary (lung) infections.
How is it diagnosed?
A diagnosis of this condition can be made using specialised tests such as urine tests, blood tests and bone marrow or liver biopsies. The diagnosis can be confirmed through molecular genetic testing which will detect a mutation (change) in the PSAP gene.
Can it be treated?
Treatment for this condition is symptomatic and supportive. This treatment aims to manage and alleviate individual symptoms and provide support for the patients and their families. There is no specific treatment available for this condition.
Do my family need to be tested?
Prosaposin 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 of prosaposin deficiency 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 prosaposin deficiency 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.