Principles of Neonatology - Chapter 80: Common Chromosomal Conditions in Newborns

Chromosomal conditions affect 1 in 150 live births and include karyotypic findings such as aneuploidy (numerical abnormalities) and smaller chromosomal microdeletions or duplications, referred to as copy number variants (structural abnormalities). Common sex-chromosome abnormalities include Turner syndrome, triple X syndrome, and Klinefelter syndrome. These sex-chromosome disorders are compatible with life and have a range of clinical features including intellectual disability, height discrepancies, and a change in reproductive function. This group of disorders is difficult to diagnose prenatally. The most common prenatally diagnosed aneuploidies include trisomy 13, trisomy 18, and trisomy 21. Trisomy 13 and 18 are most known for their ability to be diagnosed on prenatal ultrasound by multiple anomalies and their low survival rate. Trisomy 21, the most commonly discussed aneuploidy, is characterized by a widely variable phenotype with intellectual disability and an average life span of 6 decades. Microdeletion and microduplication syndromes include a host of phenotypes that typically involve some level of intellectual disability and characteristic physical features. DiGeorge syndrome, for example, exhibits a highly variable phenotype, even between first-degree relatives. Other notable microdeletion/microduplication disorders include deletion 1p36, Wolf-Hirschhorn, cri-du-chat, Williams-Beuren, and WAGR (Wilms tumor–aniridia–genitourinary anomalies–retarded development) syndromes. All aneuploidies, including sex chromosome disorders, can be identified through standard karyotype testing. All microdeletions and microduplications require testing through a chromosomal microarray.