Disorders Involving Sex Chromosomes

DISORDERS INVOLVING SEX CHROMOSOMES

Klinefelter syndrome is caused by meiotic nondisjunction and is a common causeof male hypogonadism. The most common karyotype is 47,XXY. Lab studies show elevated FSH and LH with low levels of testosterone. Clinical findings include testic-ular atrophy, infertility due to azoospermia, eunuchoid body habitus, high-pitched voice; female distribution of hair; and gynecomastia.

Turner syndrome is a common cause of female hypogonadism. The most commonkaryotype is 45,X. The second X chromosome is necessary for oogenesis and normal development of the ovary. Clinically, patients fail to develop secondary sex charac-teristics and have short stature with widely spaced nipples. Other features include gonadal dysgenesis with atrophic streak ovaries; primary amenorrhea; and infertility.

Clinical features involving other organ systems include cystic hygroma and web-bing of the neck; hypothyroidism; congenital heart disease (preductal coarctation of the aorta and bicuspid aortic valve); and hydrops fetalis. Females with 45,X/46,XY mosaicism are at risk for gonadoblastoma.