Gene : ALPL

What is Hypophosphatasia?

Hypophosphatasia is a rare inherited disorder caused by deficiency of the alkaline phosphatase (ALP) enzyme. Deficiency of the ALP enzyme leads to defective mineralization of bones and teeth to make them strong and rigid. The spectrum of this condition is wide and it ranges form severe to mild. The most severe form is apparent before birth. Affected children do not form their skeletons properly and are often stillborn. If they survive, they have short, bowed limbs, soft skull bones, and abnormally shaped chest. They often die from respiratory insufficiency in the first few weeks to months of life. Due to increased calcium levels in the blood, poor feeding, poor growth, and seizures are common. The less severe form has variable clinical presentation and onset. Some affected individuals suffer unexplained fractures; others might suffer premature loss of baby teeth. Abnormal head shape, short stature, motor delay, and abnormal gait might be observed in affected individuals. Some individuals can develop seizures and muscle weakness. In some instances, affected individuals do not develop symptoms until later in adulthood. They often suffer early tooth loss and slow healing fractures. Individuals affected by the mildest form of the disease have abnormal tooth development but do not suffer from other complications. There is no cure for hypophosphatasia; however medical surveillance and care may help to improve some symptoms and overall condition of life. Hypophosphatasia is caused by pathogenic variants in the ALPL gene.

How is hypophosphatasia inherited?

Hypophosphatasia is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for hypophosphatasia. However, the risk to have a child affected with hypophosphatasia is increased. Testing of reproductive partners is recommended for carriers of hypophosphatasia.

How common is hypophosphatasia?

Hypophosphatasia is a rare condition that affects all ethnicities. Severe hypophosphatasia is estimated to occur in 1 in 100,000 newborns. Hypophosphatasia is much more common in the Canadian Mennonite population, with occurrence of the perinatal lethal form reported at 1 in 2500 newborns.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems




Carrier Rates
Detection Rate
Carrier Frequency
East Asian 91% 1 in 203
General Population 95% 1 in 158
Northern European Caucasian 95% 1 in 274

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