Monochorionic diamniotic twins concordant for anencephaly: a case report

Anencephaly occurs in 1.4-4.7 per 10,000 deliveries and is thought to result from failed closure of the anterior neuropore at 24-26 days post fertilization. Among twins, risk for congenital malformations is greatest among monozygotic twins. Several occurrences of twin pairs being discordant for neural tube defects have been reported: 1 twin affected with anencephaly and co-twin affected with holoprosencephaly, spina bifida or encephalocele, is consistent with a multifactorial pattern of inheritance. We present an instance of monochorionic diamniotic twins concordant for anencephaly.

An 18-year-old, gravida 1, para 0, Caucasian woman presented with monochorionic diamniotic twin gestation at 22 weeks. Prenatal ultrasound identified polyhydramnios, anencephaly, ventricular septal defect and suspected rocker-bottom feet in twin A. Twin B was identified as anencephalic, with left renal agenesis and spinal distortion visualized on ultrasound. Postnatal cytogenetic evaluations of placenta, umbilical cord blood and fetal skin samples from both twins revealed 46,XX karyotypes.

A rare case of a monochorionic diamniotic gestation concordant for anencephaly is presented. Previously published reports of concordant twin anencephaly have postulated a possible autosomal recessive or multifactorial mode of inheritance. Subsequent pregnancies with anencephaly or other open neural tube defects would indicate a mendelian process.