Hypophosphatasia: Diagnostic Clues for the Dental Practitioner

Hypophosphatasia is characterized by a defect in bone and tooth mineralization and a deficiency in bone and serum alkaline phosphatase activity. It is an inborn error of metabolism with a wide clinical spectrum, ranging from premature loss of primary teeth to neonatal death.¹ The term ‘hypophosphatasia’ was first used by Rathbun in 1948, who described the case of a young boy who died at two months of age from what appeared to be a severe form of rickets with weight loss and low levels of alkaline phosphatase.² The prevalence of hypophosphatasia of this severity is estimated to be one in 100,000, based on paediatric hospital records in the USA.³ However, the incidence of moderate forms of hypophosphatasia is largely unknown and expected to be much higher.⁴

Hypophosphatasia may be expressed through a number of clinical presentations ranging from stillbirth with skeletal hypomineralization to premature loss of teeth in the absence of systemic and/or skeletal abnormalities. There are six recognized clinical forms of hypophosphatasia,⁴ categorized primarily on the age at the time of diagnosis. These are summarized in Table 1. Previous reports have illustrated a range in clinical presentations for hypophosphatasia with varying inheritance patterns.^5,6,7 However, the role of the dental practitioner in diagnosing the condition, particularly in young children, is often less discussed.