Low maternal serum unconjugated estriol during prenatal screening as an indication of placental steroid sulfatase deficiency and X-linked ichthyosis.

Placental sulfatase deficiency is an X-linked metabolic defect that occurs in about 1 in 2,000 to 5,000 males. It is associated with congenital ichthyosis. In this report, the authors document a case of placental sulfatase deficiency detected during routine prenatal screening of maternal serum by the triple test: serum alpha-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG). At 16-weeks gestation, her AFP was 20.9 IU/mL (multiple of the median [MOM] 0.83), hCG was 14.4 mIU/L (MOM 0.42) and her uE3 was 0.01 nmol/L (MOM 0.01). The extremely low uE3 indicated a possible placental sulfatase deficiency, congenital adrenal hypoplasia, or other unknown abnormality. On receiving this information, the obstetrician obtained a family history that was consistent with ichthyosis in the maternal grandfather and his siblings. Biochemical analysis of placenta documented the lack of sulfatase activity. This case illustrates that an extremely low level of maternal uE3 should prompt investigation of the family for evidence of X-linked ichthyosis associated with placental sulfatase deficiency.