Mosaic Trisomy 18 in a Five-Month-Old Infant

Individuals with mosaic trisomy 18, only approximately 5% of all trisomy 18 cases, carry both a trisomy 18 and an euploid cell line. Their clinical findings are highly variable, from the absence of dysmorphic features to the complete trisomy 18 syndrome. A five-month-old daughter of a 38-year-old mother, with vomiting and feeding problems, was referred to our department. She was undernourished and had axial hypotony and developmental delay, an irregular pattern of hypopigmentation on the right side of the abdomen, and moderate sagittal body asymmetry with left-side muscular hemihypotrophy. Mild craniofacial dysmorphy included dolichocephaly, frontal bossing, prominent occiput, long downslanting palpebral fissures, hypertelorism, and retrognathia. A complex heart defect with atrial and ventricular septal defects, pulmonary artery stenosis, and bicuspid aortic valve was identified. Cytogenetic analysis revealed mosaic trisomy 18 with trisomy in 90% of peripheral lymphocytes and 17% of skin fibroblasts. This case adds to our knowledge of the phenotypic spectrum and the natural history of mosaic trisomy 18 by adding a dysmorphic feature and a cardiac abnormality that, to the best of our knowledge, had not been previously described. 1. Introduction Mosaicism is the presence of more than one cell line in the same individual, and it occurs in approximately 5% of trisomy 18 cases [1]. These individuals carry both a trisomy 18 and an euploid cell line. Their clinical findings are highly variable in a phenotypic spectrum that spans from the absence of dysmorphic features with normal intelligence to the complete trisomy 18 syndrome [2]. Edwards syndrome, the complete trisomy 18 phenotype, affects approximately 1 in 6,000 live births, of which only 10% survive beyond the first year of life [3]. It is characterized by multiple congenital anomalies, feeding difficulties, and severe psychomotor, and growth retardation. Some distinctive features are microphthalmia, micrognathia, clenched fingers, and rocker-bottom foot with prominent calcaneus. As these characteristics may be totally absent in mosaics, a high level of suspicion for the possibility of a mosaic cytogenetic abnormality is required. A 5-month-old girl with mosaic trisomy 18 is reported. This case adds to our knowledge of the spectrum and natural history of mosaic trisomy 18, for which case reports are a major contribution. It adds a dysmorphic feature and cardiac abnormality that, to the best of our knowledge, have not been previously described. 2. Case Presentation A female fifth child of a 38-year-old