Pericentric Inversion of Chromosome 9 in Twins With Cyclopia: A Rare Entity

Abstract

Pericentric inversion of chromosome 9 (inv(9)) is one of the most common variants seen in a normal human karyotype that occurs during meiosis. Despite being categorized as a normal variant, some studies using classical cytogenetics have recently shown that inv(9) could be associated with azoospermia, congenital anomalies, growth retardation, and rarely with abnormal karyotype. However, there is no reported association with cyclopia. Interestingly this genetic variant involves twin fetuses. A 36-year-old multiparous lady with dichorionic diamniotic twin pregnancy presented to the fetomaternal unit with fetal growth restriction at 34 weeks of gestation. An ultrasound scan revealed both have microcephaly, fisting hands, holoprosencephaly, and proboscis suspicious of Patau syndrome. Amniocentesis was not issued due to late pregnancy and guarded prognosis. The mother presented with pre-eclampsia at 35 weeks of gestation. The pregnancy managed to prolong up to 36 weeks after which caesarean section was performed due to the leading twin being in a transverse lie. Two baby twin girls were born 3 minutes apart with microcephaly and cyclops appearance. Chromosomal analysis of both twins revealed similar karyotypes of 46, XX, inv(9)(p11,q13). Pericentric inversion of chromosome 9 is regarded as a normal chromosomal variation in the general population, but in twins with cyclops is considered rare. Early referral to a tertiary hospital for twin management is highly required. It may identify fetuses with such abnormalities and counsel the parents with appropriate management.

Keywords: alobar holoprosencephaly; cyclopia; dichorionic diamniotic twins; patau syndrome; pericentric inversion of chromosome 9.

Figure 1. Ultrasound images of the twins at 35 weeks. The first twin is on the left, both twins show proboscis

Figure 2. The first twin (left) had a true cyclopia, and the second twin (right) had synophthalmos features