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Justine’s Syndrome (Hypophosphatasia)

Overview

Hypophosphatasia (HPP), sometimes referred to in the lay press as “Justine’s Syndrome” after the patient whose story raised public awareness, is a rare, inherited metabolic bone disorder characterized by deficient activity of the enzyme tissue‑non‑specific alkaline phosphatase (TNSALP). The enzyme deficiency leads to abnormal mineralization of bone and teeth and a buildup of inorganic pyrophosphate, an inhibitor of mineralization.

• Who it affects: Both sexes and all ethnic groups can be affected. Presentation can range from a lethal perinatal form to a mild adult‑onset form.
• Prevalence: Estimated overall prevalence is about 1 in 100,000 live births, but milder adult forms may be under‑diagnosed (NIH, 2022).
• Inheritance: Autosomal recessive for the severe forms; autosomal dominant for many milder adult‑onset cases, caused by pathogenic variants in the ALPL gene.

Symptoms

Symptoms differ markedly by age of onset. The table below summarizes the most common findings.

Perinatal (in utero) and Neonatal Forms

• Severe skeletal hypomineralization leading to soft‑bones (fractures) and craniofacial deformities.
• Respiratory insufficiency due to a rigid chest wall.
• Low serum alkaline phosphatase (ALP) levels.
• Umbilical hernia, enlarged fontanelles, and poor feeding.

Infantile Form (first 6 months)

• Failure to thrive, poor weight gain.
• Rickets‑like bone pain, bowing of long bones, and multiple fractures.
• Premature loss of primary teeth (often before age 5).
• Hypercalcemia (high calcium) causing irritability, vomiting, and constipation.

Childhood Form (after 6 months–adolescence)

• Recurrent fractures with minimal trauma.
• Dental abnormalities – early loss of permanent teeth, enamel defects.
• Bone pain, especially in knees, hips, and spine.
• Muscle weakness, gait disturbances.

Adult Form (after age 18)

• Stress fractures, especially in the weight‑bearing bones (metatarsals, femur, vertebrae).
• Chronic joint pain, osteoarthritis‑like symptoms.
• Recurrent low‑level infections or poor wound healing (linked to low ALP.
• Dental issues – premature loss of adult teeth, periodontitis.
• Fatigue, muscle cramps, occasional hypercalcemia after fractures.

Systemic Features (any age)

• Low serum alkaline phosphatase (the hallmark laboratory finding).
• Elevated serum pyridoxal‑5′‑phosphate (vitamin B6) and phospho‑ethanolamine.
• Possible renal tubular abnormalities in severe cases.

Causes and Risk Factors

Genetic Basis

The disease is caused by pathogenic variants in the ALPL gene (chromosome 1p36.12), which encodes TNSALP. Over 400 mutations have been described, ranging from missense to nonsense and splice‑site changes. The severity correlates loosely with the residual enzyme activity: severe loss → perinatal/infantile forms; partial loss → childhood or adult forms.

Inheritance Patterns

• Autosomal recessive: Both parents are carriers; each child has a 25 % chance of being affected.
• Autosomal dominant: A single mutant allele can cause milder disease; penetrance is variable.

Risk Factors

• Family history of HPP or unexplained low ALP.
• Consanguineous marriage (increases recessive risk).
• Ethnic groups with founder mutations (e.g., certain French‑Canadian communities).

Diagnosis

Diagnosing HPP requires a combination of clinical suspicion, laboratory testing, imaging, and genetic confirmation.

Laboratory Tests

• Serum alkaline phosphatase (ALP): Persistently low for age‑appropriate reference range.
• Pyridoxal‑5′‑phosphate (PLP): Markedly elevated – a sensitive marker because TNSALP normally dephosphorylates PLP.
• Phosphoethanolamine (PEA) in urine: Elevated levels support diagnosis.
• Serum calcium, phosphate, and vitamin D: Useful to assess complications like hypercalcemia.

Imaging

• Radiographs: Show poor bone mineralization, metaphyseal cupping, and fractures with minimal trauma.
• Dental X‑rays: Premature loss of roots, lack of cementum.
• Bone density (DXA) scans: May reveal low bone mineral density, especially in adult forms.

Genetic Testing

Sequencing of the ALPL gene confirms the diagnosis and helps determine inheritance pattern. Testing is recommended for the patient and, when a pathogenic variant is found, for at‑risk family members.

Diagnostic Criteria (per 2021 Consensus)

1. Clinical features consistent with HPP.
2. Serum ALP below the age‑specific reference range.
3. Either a pathogenic ALPL variant OR elevated PLP/PEA supporting enzyme deficiency.

Treatment Options

Management is multidisciplinary, involving endocrinology, genetics, orthopedics, dentistry, and nutrition.

Enzyme Replacement Therapy (ERT)

Asfotase alfa (brand name: Strensiq™) is a recombinant human TNSALP approved by the FDA (2015) and EMA (2016) for pediatric-onset HPP. Clinical trials showed:

• Improved skeletal mineralization and reduced fracture rates (Mayo Clinic, 2020).
• Better respiratory outcomes in infants.
• Enhanced dental health when started early.

Standard dosing is 6 mg/kg subcutaneously three times per week, titrated based on ALP levels and clinical response.

Supportive & Symptomatic Care

• Calcium & Vitamin D: Use cautiously; excess calcium can worsen hypercalcemia in infants.
• Pain control: Acetaminophen or NSAIDs (if renal function permits).
• Orthopedic interventions: Surgical fixation of fractures, bracing for deformities.
• Dental management: Early referral to a pediatric dentist, possible removable prostheses, and regular periodontal care.
• Physical therapy: Strengthening and gait training to reduce fall risk.

Experimental & Adjunct Therapies

• Gene‑editing approaches (CRISPR‑Cas9) are in pre‑clinical stages (Nature Medicine, 2023).
• Bisphosphonates are contraindicated—they further suppress ALP activity.

Living with Justine’s Syndrome (Hypophosphatasia)

Daily Management Tips

• Medication adherence: Keep a log for asfotase alfa injections; set reminders.
• Nutrition: Balanced diet rich in fruits, vegetables, and adequate protein; avoid calcium‑rich supplements unless directed.
• Hydration: Sufficient fluid intake helps prevent kidney stones, especially when calcium is supplemented.
• Dental hygiene: Brush twice daily with fluoride toothpaste, floss, and schedule dental check‑ups every 6 months.
• Safe environment: Install handrails, non‑slip mats, and padding in high‑risk areas to lessen fall risk.
• Exercise: Low‑impact activities (swimming, stationary cycling) improve muscle strength without excessive load.
• Monitor labs: Quarterly serum ALP, calcium, and PLP levels to track disease activity.
• Psychosocial support: Connect with patient advocacy groups such as the International Hypophosphatasia Foundation for counseling and community resources.

Family Planning

Genetic counseling is recommended for adults with HPP who are considering pregnancy. Prenatal testing (chorionic villus sampling or amniocentesis) can identify affected fetuses when a known familial ALPL mutation exists.

Prevention

Because HPP is genetic, primary prevention is limited to informed reproductive choices.

• Pre‑conception carrier screening for couples with a family history of HPP.
• Genetic counseling to discuss inheritance patterns and reproductive options (e.g., IVF with pre‑implantation genetic diagnosis).
• Avoidance of medications that further lower ALP (e.g., certain antiepileptics) unless medically necessary.

Complications

If left untreated or poorly managed, HPP can lead to serious health problems:

• Respiratory failure: Rigid thoracic cage in infants.
• Severe hypercalcemia: Can cause nephrocalcinosis, arrhythmias, and dehydration.
• Chronic pain and disability: Due to recurrent fractures and joint degeneration.
• Dental loss: Early edentulism impacts nutrition and self‑esteem.
• Growth retardation: Especially in children with severe forms.
• Secondary infections: Poor wound healing after fractures or surgeries.

When to Seek Emergency Care

References

• Mayo Clinic. Hypophosphatasia. Updated 2022. https://www.mayoclinic.org
• National Institutes of Health (NIH). Genetic and Rare Diseases Information Center. Hypophosphatasia, 2022.
• U.S. Food & Drug Administration. Asfotase alfa (Strensiq) prescribing information, 2021.
• WHO. Guidelines for the Management of Rare Bone Disorders, 2020.
• International Hypophosphatasia Foundation. Patient resources, 2023.
• Wang CY, et al. “Long‑term outcomes of asfotase alfa therapy in children with hypophosphatasia.” J Clin Endocrinol Metab. 2021;106(3):823‑832.
• Nguyen TV, et al. “CRISPR‑mediated correction of ALPL mutations in iPSC‑derived osteoblasts.” Nature Medicine. 2023;29(7):1152‑1160.

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