Non‐Mosaic Trisomy 9: Further Delineation of the Clinical Phenotype

Non-mosaic trisomy 9 (NMTS9) is a rarely described chromosomal abnormality because most affected pregnancies result in first trimester spontaneous abortions, although survival to delivery is possible. In contrast, the phenotypic features of mosaic trisomy 9 have been well described in the literature as these individuals can survive to birth and beyond. Therefore, a better understanding of the phenotypic spectrum of NMTS9 is needed to provide appropriate perinatal counseling. The phenotype from three fetal and one neonatal case of NMTS9, as defined by chromosome analysis in multiple tissues, is consistent with the existing literature and includes narrow forehead, midface hypoplasia, microphthalmia, clouded corneas, blepharophimosis, rounded nasal tip, broad/prominent nasal bridge, low-set ears with and without malformations, short and broad neck, cerebellar abnormalities, a wide range of cardiac anomalies including ventricular and atrial septal defects as well as valve dysplasia, congenital diaphragmatic hernia, hydronephrosis, and hypoplastic genitalia, multiple contractures, multiple dislocations, and talipes equinovarus. We also report an expansion of the cardiac, genitourinary, and renal phenotypes. This combined phenotype based on prenatal imaging and fetal/postnatal autopsy further delineates the clinical phenotype of NMTS9.