Hypophosphatasia – Childhood onset

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Childhood – onset hypophosphatasia 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. 

Unfortunately, the global prevalence is unknown. However there have been around 130 cases reported to date. There is a prevalence of 1:100,000 has been found in Ontario.  

Childhood onset hypophosphatasia typically begins to manifest after six months of age to five years of age. In addition, the signs and symptoms of childhood-onset hypophosphatasia vary greatly but the signs and symptoms are:  

• Rickets  
• Short stature 
• Early loss of baby teeth 
• Bulging eyes 
• Waddling gait  
• Muscle tissue disease (myopathy)  
• Skin dimple over apex of long bone angulation 
• Dental cavities 
• Long narrow head (Dolichocephaly)

Childhood onset hypophosphatasia 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 children with hypophosphatasia. The differential diagnosis of adult HPP are: osteogeneis imperfecta, campolmelic dysplasia, hypophosphatemic rickets and achondorgeneis. 

Treatment of Childhood onset hypophosphatasia has been supportive in nature. The treatment is to use rehabilitation strategies in order to minimize function limitations. Surgery is also used to manage some fractures, but in rare cases doctors have advised using a modified diet in order to try and correct the hypercalcaemia. In recent history enzyme replacement therapy has been used to treat childhood-onset hypophosphatasia. The enzyme asfotase alfa has been used, which has had positive results. 

Milder forms of hypophosphatasia can either have autosomal recessive or autosomal dominant inheritance patterns. 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 when both of the genes are not working child-onset hypophosphatasia will develop. For a child to develop child-onset hypophosphatasia they will need to inherit one non-working gene from each parent. The parents do not necessarily need to be diagnosed with child-onset 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 child-onset hypophosphatasia. There is a: 

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

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This information about metabolic diseases is provided by Metabolic Support UK and is intended for educational purposes only. It should not be used for diagnostic or treatment purposes.

Should you require more detailed information please contact Metabolic Support UK by email (contact@metabolicsupport.org) or by telephone ( 0800 652 3181). For specific medical information regarding a disorder or individual please contact your GP or Paediatrician. Metabolic Support UK accepts no responsibility for any errors or omissions nor does Metabolic Support UK assume any liability of any kind for the content of any information contained within this summary or any use that you may make of it.