Prenatal diagnosis of left isomerism: A case report

Situs solitus is defined as normal development and positioning of the thoracic and abdominal organs. Heterotaxy syndromes describe a spectrum of abnormal organ location including conditions such as asplenia and polysplenia and are best classified by the morphology of the cardiac atria as right and left isomerism. In addition, heterotaxy syndromes are present in about 2-24% of children with congenital heart defects (CHD). A 31-year old G2P1 caucasian woman presented at 13 weeks of gestation for routine first trimester assessment. The stomach was present but located centrally rather than on the left side of the abdominal cavity and the cardiac axis deviated to the left. At 17 weeks, the left superior vena cava and the aorta had obviously smaller diameter than the pulmonary artery. Fetal karyotype was normal (46XY), but Whole Exome Sequencing detected two missense variants of uncertain significance in the gene PKD1L1. The infant was born by cesarean section at 38 weeks and the diagnosis was confirmed after birth. Left isomerism is characterized by “double” left structures and underdevelopment or absence of right structures. The prognosis depends mainly on the severity of the heart defects and the development of hydrops.