Trisomy 9 Mosaicism in an Extremely Low Birth Weight Infant

Trisomy 9 mosaicism is a rare chromosomal abnormality with distinct and recognizable clinical features. In this report, we present an extremely low birth weight (ELBW) infant with trisomy 9 mosaicism. A male preterm infant born at 31+3 weeks of gestation, weighing 922 g, was delivered by cesarean section. Prenatal findings revealed severe intrauterine growth restriction and oligohydramnios. The result of non-invasive prenatal test was a low risk for chromosomal anomalies including trisomy 9. After birth, dysmorphic features were present, such as microcephaly, palpebral fissure, low set ears, a bulbous nose, micrognathia, and a high-arched palate. He also had a single umbilical artery, bilateral inguinal hernia, and cryptorchidism. Intra-organ evaluation revealed ventriculomegaly, mesocardia, absent right brachiocephalic trunk with double superior vena cava, and bilateral renal hypoplasia. He needed the respiratory support of a humidified high-flow nasal cannula until 4 months of corrected age. He had feeding difficulties requiring tube feeding because of poor oral sucking. The result of a postnatal chromosome study confirmed trisomy 9 mosaicism. To the best of our knowledge, this is the first case of an ELBW infant with trisomy 9 mosaicism in South Korea.