Introduction Trisomy 21 (Down syndrome) is the most common trisomy in live-born infants and in spontaneous abortions. British physician John Langdon Down first described the syndrome in 1866. The chromosomal abnormality was discovered in 1959 by French geneticist Jerome Lejeune,…
Introduction Trisomy 18 is the second most common autosomal trisomy (after trisomy 21). Disorder Definition Trisomy 18, also called Edwards syndrome, results from the presence of an extra copy of chromosome 18. Prevalence and Epidemiology Trisomy 18 is the second…
Introduction Trisomy 13, also known as Patau syndrome, is one of the three most common trisomy syndromes. It is often diagnosed prenatally by the identification of one or more congenital abnormalities seen on ultrasound (US). Trisomy 13 is associated with…
Introduction Chromosome abnormalities are often the cause of early pregnancy loss, fetal malformations, and stillbirth. Triploidy is a lethal chromosome abnormality caused by the presence of a complete extra set of chromosomes ( Fig. 148.1 ); it can lead to…
Introduction Aneuploidy is a chromosomal anomaly in which the number of one or more chromosomes is abnormal. Normal human somatic cells (i.e., nonegg or sperm cells) carry 46 chromosomes: two copies of each of the 22 autosomal chromosomes and two…
Introduction The VATER association is a nonrandom association of congenital malformations that include v ertebral anomalies, a nal atresia, t racheo e sophageal fistula, and r enal and r adial limb anomalies. This definition has been expanded to include vascular…
Introduction Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by abnormal cholesterol synthesis. SLOS was originally named RSH syndrome, derived from the surnames of the first three families identified with this disorder. SLOS is characterized by growth failure, cognitive…
Introduction Sirenomelia is a rare congenital disorder that was previously considered a severe form of caudal regression, although it is currently considered a completely different entity. Also known as the mermaid syndrome , it is characterized by a variable degree…
Introduction Tuberous sclerosis, also known as the tuberous sclerosis complex (TSC), is a disorder of cellular differentiation, proliferation, and migration in early development that variably affects multiple organ systems. First described in 1862 by Friedrich von Recklinghausen, TSC is characterized…
Introduction Autosomal recessive pontocerebellar hypoplasias (PCHs) are a group of severe neurodegenerative disorders affecting the cerebellum and pons. This disease appears in fetal or neonatal life with subsequent pontocerebellar degeneration, progressive microcephaly, and atrophy of the cerebral cortex. Most affected…