Hypophosphatasia – Infantile onset
What else is it called?
Infantile hypophosphatasia is also known as:
- Infantile rathburn disease
- Infantile phosphoethanolaminuria
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What causes it?
I-HPP is caused by a problem in the ALPL gene, the ALPL genes provides instructions for a specific protein known as tissue non-specific alkaline phosphatase. By having a problem means that the body will be unable to use calcium for bone calcification which means that bones will be fragile.
How common is it?
The global prevalence of I-HPP is unknown. However, around 90 cases have been reported to date.
What are the signs and symptoms?
The manifestations of I-HPP begin around birth. The signs and symptoms are:
- Poor feeding
- Failure to thrive
- Short stature
- Soft bones
- Bowing of limbs
- Kidney damage
- Early fusion of bones
- Enlarged joints
How is it diagnosed?
I-HPP is diagnosed using laboratory and molecular genetic testing of the ALPL gene in order to detect mutagens. Samples are also taken and analysed in order to read your plasma pyrophosphate and urinary pyrophosphate and phosphoethanolamine levels, which are higher in infants with hypophosphatasia. I-HPP can also be diagnosed using ultrasound as with an ultrasound the skeletal deformations can be seen as the develop in the womb.
The differential diagnosis of I-HPP are: osteogeneis imperfecta, campolmelic dysplasia, hypophosphatemic rickets and achondorgeneis.
Can it be treated?
I-HPP can be treated using enzyme replacement therapy using a drug known as asfotase alfa. People taking asfotase alfa have shown improvements in their health. Pain symptoms can also be treated using a teriparatide and Non-steroidal anti-inflammatory drugs. In addition your doctor may also recommend a specialist diet to try and treat the hypercalcinaemia, which is avoid vitamin and mineral supplements for rickets.
Do my family need to be tested?
I-HPP is an autosomal recessive inherited disease. Humans are made up of DNA and the DNA is made up of chromosomes. Genes are sections of DNA which provide instructions to produce a protein that has a specific function. When there is an issue with a particular gene it causes the protein to be made incorrectly leading to disease. Humans inherit chromosomes from both their mother and father in the forms of eggs and sperm and these chromosomes determine the child’s characteristics. An inherited autosomal recessive disease is a disease that a child will inherit from their parents. Every human has two genes needed to make a functioning TNSALP and I-HPP will develop when both of the genes are not working. For a child to develop hypophosphatasia they will need to inherit one non-working gene from each parent. The parents do not necessarily need to be diagnosed with hypophosphatasia to pass it on, they can also be carriers. A carrier is someone who possess’ one non-working gene but does not have the disease because the other gene is working correctly.
In the event that both of the parents are carriers of type two progressive intrahepatic cholestasis. There is a:
- 25% chance that one of the children will be unaffected by I-HPP and will not be a carrier.
- 25% chance that the child will inherit I-HPP.
- 50% chance that the child will be unaffected by I-HPP will be a carrier.