Benign prenatal hypophosphatasia: a treatable disease not to be missed.

Prenatal bowing of the long bones is often associated with severe bone dysplasias. We report a child who presented marked bowing of the long bones at birth but showed a relatively benign postnatal course with spontaneous improvement of bowing. The fetal imaging showed normal skeletal mineralization and normal chest and abdominal circumferences despite the limb bowing and shortening. Decreased serum alkaline phosphatase activity and elevated urine phosphoethanolamine was biochemically evident, and compound heterozygous mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene were identified, which confirmed the diagnosis of a benign form of prenatal hypophosphatasia. Benign prenatal hypophosphatasia should be considered in the differential diagnosis of congenital bowing of the long bones.