ORTHOPEDIC CASES / Hypophosphatasia (Congenital)

The congenital form of hypophosphatasia is a rare error of metabolism characterized by defective bone and teeth mineralization. The birth prevalence is 1/100,000. The mutation in the ALPL gene results in reduced activity of tissue nonspecific alkaline phosphatase. The severity of hypophosphatasia is highly variable, ranging from intrauterine death due to the defective skeletal mineralization to premature loss of teeth only (odontohypophosphata-sia). Fractures and pseudo-fractures are common. Spinal deformity such as scoliosis and prominent scapula have also been described. Depending on the age of diagnosis, clinical forms are the following:

Fig. 1.16 Rhizomelic shortening of upper extremities. There is a characteristic prominence of muscle attachment of the humerus

• The childhood form with doliocephalic skull, enlarged joints and delay in ambulation, short stature and waddling gait;

• The adult form includes primarily autosomal dominant inheritance with foot and thigh pain, stress fractures of metatarsal bones, and femoral pseudo-frac-tures (Figs. 1.17–1.19).

• The lethal perinatal form with intrauterine impaired mineralization;

• The infantile form with respiratory complications because of rachitic chest wall deformities;