Trisomy 9 mosaicism: a genetic disorder with complications-a case report

Trisomy 9 is a rare chromosomal disorder that may occur as complete, partial, or mosaic trisomy. Trisomy 9 mosaicism is often incompatible with life and typically involves multiple congenital anomalies, especially affecting the limbs, craniofacial features, nervous system, and cardiovascular system. However, pulmonary complications are rarely reported.

We present an African American female infant, at 37 weeks and 2 days, diagnosed prenatally with trisomy 9 mosaicism (49%), identified via fetal echocardiogram that revealed multiple cardiac anomalies and intrauterine growth restriction. The infant exhibited micrognathia, dysmorphic facial features, absent external ears, and a two-vessel umbilical cord. Owing to critical airway obstruction from micrognathia, she was intubated at birth. After transitioning to non-invasive ventilation, her respiratory status deteriorated, and an echocardiogram showed an unrestrictive patent ductus arteriosus. She later experienced a pulmonary hypertensive crisis requiring re-intubation, high fraction of inspired oxygen, inhaled nitric oxide, and inotropes, followed by another transient pulmonary hypertensive crisis after patent ductus arteriosus closure. The infant was discharged home with oxygen. Her hospital course was complicated by various abnormalities, including mandibular distraction surgery, hearing loss from absent external ear canals, and retinopathy of prematurity, a rare condition in term infants. She also required gastrostomy tube placement for feeding intolerance and was diagnosed with supratentorial ventriculomegaly and corpus callosum thinning. Orthopedic evaluation revealed bilateral hip dysplasia, requiring closed reduction and Pavlik harness. A follow-up echocardiogram confirmed patent ductus arteriosus closure without pulmonary hypertension. Seizures, obstructive sleep apnea, and a persistent dry skin condition led to further genetic evaluation as an outpatient.

This case is unique for several reasons: micrognathia requiring distraction, absent external ears, severe pulmonary hypertension requiring patent ductus arteriosus closure, and long-term oxygen therapy. To our knowledge, this is the first reported trisomy 9 mosaicism case with such a severe pulmonary hypertensive crisis necessitating aggressive intervention. Although historically associated with poor outcomes, improved neonatal care contributes to increasing survival in infants with trisomy 9 mosaicism.