Mosaic Trisomy 9 With Severe Fetal Growth Restriction, Diaphragmatic Eventration, and Pulmonary Artery Hypoplasia With Peripheral Stenosis in a Preterm Infant: A Case Report

Mosaic trisomy 9 (T9M) is a rare chromosomal disorder characterized by the presence of an additional chromosome 9 in a proportion of somatic cells.The clinical manifestations can vary considerably, which is thought to be related, at least in part, to the proportion and distribution of trisomic cells across different tissues.Prognosis is similarly variable and remains difficult to predict.Although earlier reports suggested that greater proportions of trisomic cells may be associated with more severe clinical manifestations, this relationship is not consistent, likely because the degree of mosaicism can differ substantially between tissues and other genetic and clinical factors may also influence the phenotype.In this report, we describe a preterm infant with significant fetal growth restriction and multiple dysmorphic features whose hospital course was complicated by respiratory distress and feeding difficulties.While prematurity was likely an important contributor to his respiratory symptoms, diaphragmatic eventration and an underlying pulmonary artery stenosis were also considered as potential contributing factors.Pulmonary artery stenosis is not commonly emphasized among the cardiac abnormalities described in T9M and may further highlight the broad phenotypic spectrum of this condition.The infant also experienced significant feeding difficulties that ultimately required enteral tube support.This case adds to the growing clinical spectrum of T9M and illustrates the challenges of relating the observed phenotype to the degree of mosaicism in an individual patient.