Prenatal diagnosis of hypophosphatasia.

An obligate heterozygote for hypophosphatasia, gravida 3, para 2, had previously delivered a female infant who had shortening of the extremities and could not maintain respirations because of the pliability of the thorax. The infant had undermineralization of the skeleton, low serum alkaline phosphatase activity, and increased urinary phosphoethanolamine excretion; autopsy corroborated the diagnosis of congenital lethal hypophosphatasia. For the current pregnancy, uterine sonograms demonstrated adequate growth of the head and limbs, amniotic fluid cell culture showed normal alkaline phosphatase activity; and confirmatory radiographic study showed adequate mineralization of the skeleton. A healthy female infant was delivered. Prenatal diagnosis of congenital hypophosphatasia is available, and the triad of ultrasonography, alkaline phosphatase determination in the amniotic fluid cell culture, and radiography of the fetus is reliable in establishing the diagnosis.