Chromosomal Abnormalities

Published on 06/06/2015 by admin

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Last modified 06/06/2015

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118 Chromosomal Abnormalities

Since the discovery in 1959 that Down syndrome is caused by trisomy of chromosome 21, multiple syndromes have been found to have an identifiable chromosomal abnormality. These range from triplication of a complete chromosome as in Edwards syndrome (trisomy 18) to monosomies such as Turner syndrome (45,X) and to a growing number of smaller duplication and deletion syndromes. Several of the more common or illustrative chromosomal aberrations are discussed in this chapter.

Trisomy 18 (Edwards Syndrome)

Feet Rocker-bottom feet Prominent heels Hips Small pelvis Small pelvis Cardiac VSD, PDA, pulmonary hypertension ASD, VSD, PDA Renal Abnormalities in 10%-50% Large cystic kidneys Genitalia Cryptorchidism Cryptorchidism, bicornuate uterus

ASD, atrial septal defect; CNS, central nervous system; PDA, patent ductus arteriosus; VSD, ventricular septal defect.

Turner’s Syndrome (45,X)

Clinical Presentation

Females with Turner syndrome may present prenatally with features of lymphedema/hydrops and/or a congenital heart defect, in puberty due to short stature or in adulthood with premature ovarian failure (Figure 118-1). Multiple organ systems may be involved, but no single feature is pathognomonic or universally present.

Several physical features are found as a consequence of lymphatic abnormalities that include webbed neck, puffy hands and feet, dysplastic finger- and toenails, protuberant ears, and a broad chest.

Up to 45% of patients have a cardiac anomaly identified by echocardiography, most often a bicuspid aortic valve or aortic coarctation, but other cardiac anomalies such as partial anomalous pulmonary venous connection can also occur. Renal anomalies are equally frequent (40%), including renal agenesis and horseshoe kidney. Hypothyroidism may develop in 5% to 10% of girls in mid to late childhood and affects up to one-third of adult women.

Growth delay begins in childhood, but short stature may not be noticed until 5 to 10 years of age or in puberty with a blunted growth spurt. Growth hormone treatment may lead to improvement, but adult height is usually reduced.

Gonadal dysgenesis is a hallmark of Turner syndrome and typically leads to ovarian failure. Puberty occurs spontaneously in 10% of patients, and hormonal replacement therapy is necessary to achieve development of secondary sexual characteristics as well as to avoid osteoporosis and other postmenopausal complications. Nonetheless, spontaneous pregnancy has been observed in about 2% to 4% of women with Turner syndrome.

Most girls with Turner syndrome have normal developmental milestones and intelligence. About 10% of individuals experience specific learning disabilities, mental retardation, motor deficits, or difficulties with attention, maturity, and social skills. Correlation has been observed between the intellectual phenotype and the karyotype, and girls with a marker or ring chromosome have a higher prevalence of mental retardation.