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Hypophosphatasia: the importance of alkaline phosphatase in bone mineralization
S Jaruratanasirikul1, P Chanvitan
1Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat-Yai, Songkhla, Thailand.
Insights
Perinatal hypophosphatasia, a severe inherited condition, presents with skeletal deformities and extremely low alkaline phosphatase. Prenatal diagnosis via serial ultrasonography is crucial for early intervention.
Area of Science:
- Biochemistry
- Genetics
- Pediatric Medicine
Background:
- Hypophosphatasia is an inherited metabolic disorder affecting bone mineralization.
- It is caused by mutations in the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP).
- Perinatal hypophosphatasia is the most severe form, often leading to stillbirth or early infant death.
Observation:
- A neonate presented with microcephaly, a soft calvarium (caput membranaceum), and limb deformities.
- Laboratory results showed hypercalcemia, hyperphosphatemia, and undetectable alkaline phosphatase levels.
- Radiographic imaging revealed hypomineralization, skeletal deformities, and abnormal calcification patterns.
Findings:
- The case highlights the severe clinical and radiographic manifestations of perinatal hypophosphatasia.
- Extremely low alkaline phosphatase activity is a hallmark of this condition.
- The study reviews the critical role of alkaline phosphatase in bone development and mineralization.
Implications:
- Perinatal hypophosphatasia is a fatal autosomal recessive disorder.
- Prenatal diagnosis is essential for genetic counseling and family planning.
- Serial ultrasonography in the second trimester is a reliable method for prenatal diagnosis.
Abstract:
The authors describe a neonate who was diagnosed with "perinatal hypophosphatasia". The clinical manifestations in this patient were small head size, soft calvarium (caput membranaceum), and short bowing forearms and legs. Laboratory investigations revealed hypercalcemia at 12.7 mg/dl, hyperphosphatemia 8.6 mg/dl, and extremely low alkaline phosphatase 0 unit/L. Roentgenographic studies of the skull showed calcification only at frontal bone and base of the skull. Spines were small and flattened. Long bones were hypomineralized and deformed. The functions of alkaline phosphatase to bone development and mineralization were reviewed. Because perinatal hypophosphatasia is a fatal condition and inherited as an autosomal recessive pattern, prenatal diagnosis is necessary. The most reliable and suitable method in our facility is serial ultrasonography from which the diagnosis can be made by the second trimester.