Infantile hypophosphatasia

Infantile hypophosphatasia happens when changes in the ALPL gene cause very low alkaline phosphatase. Some risks are written in our DNA, passed down through families. Most severe infant cases are recessive, so both parents are usually carriers. Risk factors for infantile hypophosphatasia include a family history, two carrier parents, and parents who are related by blood. Lifestyle and environment do not cause it, but other genes and health factors can affect how severe it is.

Genetic risk factors

Infantile hypophosphatasia is caused by changes in a single gene called ALPL that lower alkaline phosphatase, an enzyme needed for healthy bones and teeth. Most babies with this condition inherit two significant ALPL changes, one from each parent, which leads to low enzyme activity. Some risk factors are inherited through our genes. Family history and the exact type of ALPL change can influence how early and how severely a child is affected.

• ALPL gene changes: Changes in the ALPL gene reduce alkaline phosphatase activity, which disrupts normal bone and tooth mineralization. This genetic change is the root cause of Infantile hypophosphatasia.

• Two altered copies: Having two disease-causing ALPL changes, one from each parent, is the main route to infantile hypophosphatasia. Carriers with only one change usually have no symptoms or milder forms. When both parents are carriers, each pregnancy has a 25% chance of an affected child.

• Variant type matters: Some ALPL changes completely turn off the enzyme, while others only dim it. More severe changes tend to bring earlier disease and stronger features. This often lines up with early symptoms of infantile hypophosphatasia.

• Compound heterozygosity: Two different ALPL changes (one on each copy) can still add up to infantile hypophosphatasia. The combined effect of both changes influences severity. Doctors may review both variants together to estimate risk.

• Dominant-negative variants: Rare ALPL changes can act in a dominant way and interfere with the working copy. These can cause childhood-onset and, rarely, infantile severity. Risk is not destiny—it varies widely between individuals.

• Family history: A previous child with infantile hypophosphatasia signals a higher chance in future pregnancies. Parents who are both carriers have a 25% recurrence risk each time. Extended family members may also be carriers.

• Parental mosaicism: Very rarely, a parent carries an ALPL change in only some egg or sperm cells. This can raise recurrence risk even if blood testing in the parent is negative. A genetics team can explain this uncommon situation.

• Parental relatedness: When parents are related by blood, they are more likely to carry the same ALPL change. This increases the chance of autosomal recessive infantile hypophosphatasia. Genetic counseling can clarify personal risk.

• Ancestry founder variants: Certain communities have higher carrier rates due to founder changes in ALPL. For example, specific recurrent variants have been reported in Japanese and Mennonite populations. Testing strategies may be tailored when such ancestry is known.

• De novo variant: Sometimes an ALPL change appears for the first time in a child. In these cases, infantile hypophosphatasia can occur without a family history. Recurrence risk for future children is usually low unless mosaicism is present.

Transmission

Infantile hypophosphatasia is a genetic condition, not an infection, so it doesn’t spread through touch, coughing, or close contact. It stems from changes in a gene called ALPL that affect how bones and teeth mineralize.

In most families, genetic transmission of infantile hypophosphatasia follows an autosomal recessive pattern—both parents carry one non-working copy of the gene, and with each pregnancy there is a 25% (1 in 4) chance the child will be affected. Less often, how infantile hypophosphatasia is inherited may involve a new (de novo) change in the child, or, rarely, a dominant change that can be passed from an affected parent. A genetics professional can help clarify the pattern in your family and discuss carrier testing and options for future pregnancies.

When to test your genes

Consider genetic testing if a baby shows very low alkaline phosphatase on labs, poor bone mineralization, early tooth loss, seizures that respond to vitamin B6, or unexplained fractures. Testing is also reasonable if a parent or sibling has hypophosphatasia. Results can guide enzyme replacement therapy, dental care, and family planning.

Looking at the long-term picture can be helpful. For many living with infantile hypophosphatasia, the first year of life is the most critical. Breathing problems from a soft chest, poor weight gain, and early symptoms of infantile hypophosphatasia such as delayed tooth eruption or fragile bones can signal a higher risk. Without treatment, severe forms carry a significant risk of complications and even infant death, most often from respiratory failure. With enzyme replacement therapy and careful respiratory and nutritional support, survival and quality of life have improved markedly over the past decade.

The outlook is not the same for everyone, but progress tends to depend on how early and how severely bones and breathing are affected. Some children stabilize with therapy, start sitting and walking, and experience fewer fractures over time; others may continue to need ventilatory support, feeding assistance, or surgery for skeletal problems. Growth may be slower than peers, and teeth may be affected, yet many children attend school, play, and build routines with adaptive supports. In medical terms, the long-term outlook is often shaped by both genetics and lifestyle.

Knowing what to expect can ease some of the worry. Early care can make a real difference, especially when a multidisciplinary team tracks breathing, calcium and phosphate levels, bone strength, and dental health. Talk with your doctor about what your personal outlook might look like, including how your child responds to enzyme therapy, the need for physical therapy, and plans for school and activity. As children with infantile hypophosphatasia grow into adolescence, ongoing follow-up helps detect changing needs and supports independence.

Treatment for infantile hypophosphatasia focuses on replacing the missing enzyme, easing symptoms, and preventing complications. The main therapy is asfotase alfa, an enzyme replacement given by injection that can improve bone strength, help with breathing and feeding, and reduce fracture risk; a doctor may adjust your dose to balance benefits and side effects. Supportive care can make a real difference in how you feel day to day, including nutrition support, pain control, careful dental care, and help with breathing if the chest is weak. Many children with infantile hypophosphatasia also work with a multidisciplinary team—metabolic specialists, pediatricians, dentists, physical and occupational therapists—to monitor growth, movement, calcium and phosphate levels, and to manage seizures if they occur. If you’re unsure, write down questions to bring to your next visit so your care team can tailor treatment to your child’s needs.

In most families, infantile hypophosphatasia stems from changes in the ALPL gene that lower the activity of an enzyme needed to harden bones and teeth. Often, the infantile form appears when a child inherits a gene change from both parents, so the parents are healthy but each carries one copy. A “carrier” means you hold the gene change but may not show symptoms. Less commonly, a single ALPL change is enough to cause milder features in a parent or other relative, so family patterns can look mixed. Even within the same family, severity can vary—one baby may have early symptoms of infantile hypophosphatasia in the first months of life, while a sibling only has later tooth issues. Genetic testing can identify changes in ALPL, confirm the diagnosis, and guide testing for relatives and planning for future pregnancies.

Colds or chest infections can quickly strain breathing in infantile hypophosphatasia because the ribs and chest wall may be softer than usual, so even a routine virus can lead to more work with each breath. Early symptoms of infantile hypophosphatasia can be mistaken for vitamin D–deficiency rickets or osteogenesis imperfecta; if any of these truly occur together, bone weakness and fractures can be more frequent and recovery slower. A condition may “exacerbate” (make worse) symptoms of another, so treating vitamin D deficiency, managing lung infections promptly, and avoiding long periods of immobilization all matter. High blood calcium and calcium in the urine are common in infantile hypophosphatasia; if kidney stones or chronic kidney disease are also present, the risk of dehydration, pain, and further kidney stress increases and monitoring needs to be tighter.

Seizures linked to infantile hypophosphatasia often respond to vitamin B6, but if a child also has epilepsy from another cause, some seizure medicines and long-term steroids can reduce bone strength, so the care team may adjust choices and doses. Medicines used for other bone diseases—especially bisphosphonates for osteoporosis—are generally not suitable in infantile hypophosphatasia and can worsen bone mineralization, making coordinated care across specialists essential.

How genes can cause diseases

Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.

Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.