Sex chromosome abnormalities are due to numeric abnormalities (eg, aneuploidies such as monosomy X) or structural chromosome defects (eg, isochromosome Xq leading to Turner syndrome) involving the X and Y chromosomes.

• NUMERIC ABNORMALITIES (ANEUPLOIDIES)
  • Monosomy X (45,X or Turner syndrome)
  • 47,XXY Klinefelter syndrome
  • 47,XYY
  • 47,XXX
  • Other
    • 49,XXXXY
    • 49,XXXXX
  • 45,X/46,XX mosaicism
  • 45,X/46,XY mosaicism

• STRUCTURAL ABNORMALITIES

• • Isochromosome Xq
  • X-chromosome deletions
    • Xp11.22 deletions
    • Xp22.11 deletion
    • Xp22.3 deletion
    • Xp22 SHOX deletions
  • X-chromosome duplications
    • Xp11.22 microduplication
    • Xp21.22 duplication
    • Xp22.31 duplication
    • Xp26.3 microduplication
    • MECP2 duplication syndrome

Female Sex Chromosome Abnormalities

Turner syndrome  occurs when females inherit only one X chromosome–their genotype is X0 (i.e., monosomy X).

Features

1. Abnormal growth patterns.
2. They are short in stature, averaging 4 foot 7 inches as adults,
3. Distinctive webbed necks (i.e., extra folds of skin), small jaws, and high arched palates.  They generally lack prominent female secondary sexual characteristics.
4. They have exceptionally small, widely spaced breasts, broad shield-shaped chests, and turned-out elbows.
5. Their ovaries do not develop normally and they do not ovulate.
6. The few oöcytes that they produce are destroyed by the time they are two.  They are in a sense postmenopausal  from early childhood and are sterile.
7. They can become pregnant and give birth if fertilized eggs from a donor are implanted.
8. They have a higher than average incidence of thyroid disease, vision and hearing problems, heart defects, diabetes, and other autoimmune disorders.
9. In a few individuals, there is slight mental retardation.

Frequency

Frequency range from 1 in 2,000 to 1 in 5,000 female infants.

Treatment

If diagnosed in early childhood, regular injections of human growth hormones can increase their stature by a few inches.  Beginning around the normal age of puberty, estrogen replacement therapy can result in some breast development and menstruation.  These treatments allow Turner syndrome women to appear relatively normal.

Triple-X syndrome occurs in women who inherit three X chromosomes–their genotype is XXX or more rarely XXXX or XXXXX and also called as “super-females” or “metafemales”.

Features

1. Are an inch or so taller than average with unusually long legs and slender torsos but otherwise appear normal.
2. They usually have normal development of sexual characteristics and are fertile but tend to have some ovary abnormalities that can lead to premature ovarian failure.
3. They may have slight learning difficulties, especially in speech and language skills, and are usually in the low range of normal intelligence (especially the XXXX and XXXXX individuals).
4. They frequently are very tall in childhood and tend to be emotionally immature for their size.
5. This sometimes results in teachers and other adults labeling them as troublemakers because they expect more maturity from bigger girls.  However, they are usually as emotionally mature as other girls of their age.
6. Individuals who are genetic mosaics (XX/XXX) have less noticeable symptoms.

Frequency

The frequency is approximately 1 in 1,000 female infants and it occurs more commonly when the mother is older.

Male Sex Chromosome Abnormalities

Klinefelter syndrome  males inherit one or more extra X chromosomes–their genotype is XXY or more rarely XXXY or XY/XXY mosaic.

Features

1. They have relatively high-pitched voices,
2. asexual to feminine body contours as well as breast enlargement, and
3. comparatively little facial and body hair.
4. They are sterile or nearly so, and their testes and prostate gland are small.
5. As a result, they produce relatively small amounts of testosterone.
6. Are an inch or so above average height.
7. They also are likely to be overweight.
8. They have learning difficulties as children, especially with language and short-term memory.
9. most men who have Klinefelter syndrome are sufficiently ordinary in appearance and mental ability to live in society without notice.
10. They are usually capable of normal sexual function, including erection and ejaculation, but many, if not most, are unable to produce sufficient amounts of sperm for conception.
11. Klinefelter syndrome males with more than two X chromosomes usually have extreme symptoms and are often slightly retarded mentally.  Men who are mosaic (XY/XXY) generally have the least problems.
12. They are more likely to be less interested in sex.
13. They have a higher than average risk of developing osteoporosis, diabetes, and other autoimmune disorders that are more common in women.

Frequency

The frequency of Klinefelter syndrome has been reported to be between 1 in 500 and 1 in 1000 male births.

Treatment

The feminizing effects of this hormonal imbalance can be significantly diminished if Klinefelter syndrome boys are regularly given testosterone from the age of puberty on.

XYY syndrome  males inherit an extra Y chromosome–their genotype is XYY, also called “super-males”. XYY syndrome is also referred to as Jacobs syndrome.

Features

1. They are usually tall (above 6 feet) and generally appear and act normal.
2. They produce high levels of testosterone.
3. During adolescence, they often are slender, have severe facial acne, and are poorly coordinated.
4. They are usually fertile and lead ordinary lives as adults.

Frequency

It may be as common as 1 in 900 male births to as rare as 1 in 1500 or even 1 in 2,000.