Understanding Childhood Rickets: Why Your Pediatric Doctor Screens for HPP

Rickets is a condition that affects growing bones in infants and children, leading to soft, weak bones that can bend or break easily. When your child shows signs such as infant failure to thrive, bowed legs, delayed motor milestones or unexplained fractures, your pediatrician may screen for hypophosphatasia (HPP) in addition to classic nutritional rickets. Though they share some features, rickets and HPP have different causes and treatments. Recognizing the differences can help you advocate for timely testing and appropriate care.

What Is Rickets?

Rickets refers to defective mineralization of growing bones, most often caused by vitamin D deficiency. Key points include:

• Vitamin D helps the body absorb calcium and phosphate from food.
• Without enough vitamin D, bones become soft and prone to deformities.
• Common signs in infants and toddlers:
  • Delayed growth and infant failure to thrive
  • Bowing of the legs (genu varum) or knock knees (genu valgum)
  • Enlargement of the wrists and ankles (wrist and costochondral “rachitic” beading)
  • Muscle weakness, irritability or delayed crawling and walking

Treatment usually involves vitamin D and calcium supplementation, along with dietary changes and sunlight exposure.

What Is Hypophosphatasia (HPP)?

Hypophosphatasia is a rare, inherited metabolic disorder that impairs bone and tooth mineralization. It results from mutations in the ALPL gene, which codes for the enzyme alkaline phosphatase. Low enzyme activity leads to:

• Accumulation of minerals that can’t bind properly in bone
• Poor bone strength and frequent fractures
• Dental problems such as early tooth loss
• In severe cases, breathing difficulties and failure to thrive

Because HPP can mimic the signs of nutritional rickets—especially when bowed legs or delayed growth are present—doctors often include HPP in their screening panel when classic treatment fails or lab results don’t add up.

Why Early Detection Matters

Early and accurate diagnosis of HPP versus nutritional rickets is critical:

• Nutritional rickets responds well to vitamin D and calcium.
• HPP requires specialized management; high doses of vitamin D or calcium may worsen symptoms.
• New enzyme replacement therapies are available for certain forms of HPP, improving growth, mobility and quality of life.

Delays in diagnosis can lead to repeated fractures, persistent bone pain, dental complications and growth delays.

When Your Pediatrician Screens for HPP

Your doctor may suspect HPP and order enzyme levels or genetic testing if your child shows:

• Persistent infant failure to thrive despite adequate nutrition
• Bowed legs, knock knees or fractures that don’t improve with vitamin D supplementation
• Low or borderline serum alkaline phosphatase (ALP) levels—uncommon in simple rickets
• High levels of substrates normally broken down by ALP (e.g., pyridoxal 5’-phosphate)
• Family history of early tooth loss, unexplained fractures or known HPP

In many clinics, screening begins with simple blood tests and X-rays. If ALP is low and X-rays show bone mineralization problems, your child may be referred for genetic testing to confirm HPP.

Signs and Symptoms to Watch For

While each child is unique, these features help differentiate HPP from nutritional rickets:

Feature	Nutritional Rickets	Hypophosphatasia (HPP)
Serum alkaline phosphatase (ALP)	Normal or high	Low or very low
Response to vitamin D therapy	Rapid improvement	Little or no improvement
Dental findings	Rare early tooth loss	Premature loss of baby teeth (2–3 years)
Fracture pattern	Rare in early infancy	Frequent, even before walking age
Family history	Often negative	May be positive

How Screening Works

1. Clinical Evaluation

   • Detailed growth charts review
   • Assessment of motor milestones
   • Family history of bone problems or genetic conditions

2. Laboratory Tests

   • Serum ALP (low in HPP)
   • Calcium, phosphate, parathyroid hormone (often normal in HPP)
   • Vitamin D levels (low in nutritional rickets)
   • Pyridoxal 5’-phosphate (elevated in HPP)

3. Imaging

   • X-rays of wrists, knees or long bones to evaluate bone mineralization and deformities
   • Ultrasound of chest in severe infantile HPP (to assess respiratory complications)

4. Genetic Testing

   • Confirmation of ALPL gene mutations
   • Helps classify HPP subtype (perinatal, infantile, childhood, adult)

Management Strategies

Once HPP is confirmed, treatment focuses on:

• Enzyme replacement therapy (asfotase alfa) for moderate to severe forms
• Pain management and physical therapy to support bone strength and mobility
• Dental monitoring and care for early tooth loss
• Nutritional guidance—avoiding excess calcium and vitamin D unless specifically prescribed
• Regular follow-up with a metabolic or genetics specialist

For nutritional rickets, protocols typically include:

• Vitamin D3 (cholecalciferol) supplementation
• Dietary sources of calcium and phosphorus (dairy, leafy greens, fortified foods)
• Sunlight exposure in moderation
• Monitoring of blood levels and bone X-rays until correction

Supporting Your Child at Home

• Ensure a balanced diet rich in calcium and vitamin D (unless your doctor advises otherwise).
• Encourage safe, moderate sunlight exposure—10 to 15 minutes a day for infants (with sun protection as recommended).
• Follow prescription plans closely and keep all follow-up appointments.
• Monitor growth, mobility milestones and dental development.
• Keep a record of any fractures, bone pain or new symptoms.

When to Seek Help

If your child shows any of these warning signs, speak to your pediatrician right away:

• Worsening bone pain or difficulty bearing weight
• Recurrent fractures with minimal trauma
• Signs of infant failure to thrive (poor weight gain, feeding difficulties)
• Respiratory distress or breathing problems in infants
• Early loss of baby teeth

You may also consider a free, online symptom check, using the doctor approved Ubie Symptom Checker to gather information before or after your visit.

Talking to Your Pediatrician

Prepare for your appointment by:

• Listing your child’s symptoms, their onset and pattern
• Bringing growth charts, lab results and X-ray reports if available
• Noting any family history of bone or dental issues
• Writing down questions about HPP, rickets, testing options and treatment plans

Clear communication ensures you and your doctor make informed decisions about next steps.

Key Takeaways

• Rickets and HPP can both cause infant failure to thrive and bowed legs, but they differ in cause and management.
• Low serum alkaline phosphatase is the hallmark of HPP, while vitamin D deficiency underlies nutritional rickets.
• Early screening for HPP avoids unnecessary or harmful treatments and opens the door to targeted enzyme therapy.
• Regular follow-up, nutritional support and physical therapy are essential parts of care.

Above all, trust your instincts. If your child isn’t improving as expected, ask about further testing for HPP or other metabolic bone disorders.

If you have concerns about serious or life-threatening symptoms—any sudden pain, breathing trouble, or rapid growth failure—please speak to a doctor promptly. Your pediatrician is your best resource for personalized advice and treatment.