Pyridoxine-dependent seizures associated with hypophosphatasia in a newborn.

Pyridoxine dependency and congenital hypophosphatasia are unusual metabolic disorders. We report a female infant born from healthy consanguineous parents with shortening of limbs, detected during pregnancy by ultrasonography. Immediately after delivery, the baby was admitted to the neonatal intensive care unit because of respiratory distress. A bone radiograph showed hypomineralization of all bones, and serum alkaline phosphatase was very low (10 U/L). Within the first day of life, seizures (focal clonic and tonic) started. The seizures were refractory to phenobarbital and other antiepileptic drugs. The first electroencephalogram (EEG) showed a burst-suppression pattern. Pyridoxine was administered (50 mg/kg) and completely controlled the seizures. Antiepileptic drugs were discontinued, and a maintenance dose of pyridoxine (10 mg/day) was established. A postpyridoxine EEG revealed the disappearance of the burst-suppression pattern. The patient died at age 26 days. Pyridoxine-dependent seizures, when recognized early and treated, have a more favorable prognosis. However, hypophosphatasia detected at birth almost always has a lethal outcome.