Turner Syndrome
Monosomy of X Chromosome (X0)
Most girls are born with two X chromosomes, but girls with Turner syndrome are born with only one X chromosome or they are missing part of one X chromosome. Girls with Turner syndrome are usually short in height. Girls with Turner syndrome who aren't treated reach an average height of about 4 feet 7 inches (1.4 meters). In addition to growth problems, Turner syndrome prevents the ovaries from developing properly, which affects a girl's sexual development. Because the ovaries are responsible for making the hormones that control breast growth and menstruation, most girls with Turner syndrome will not go through all of the changes associated with puberty unless they get treatment for the condition. Nearly all girls with Turner syndrome will be infertile, or unable to become pregnant on their own.
Cry of the Cat - "Cri du Chat"
Deletion of Part of Upper Arm of Chromosome 5
Cri-du-chat syndrome was first described by Lejeune et al. (1963) as a hereditary congenital syndrome associated with deletion of part of the short arm of chromosome 5. Cri-du-chat syndrome is characterized in young children by microcephaly, round face, hypertelorism, micrognathia, epicanthal folds, low-set ears, hypotonia, and severe psychomotor and mental retardation. One of the most characteristic features in newborn children is a high-pitched cat-like cry that is usually considered diagnostic for the syndrome.
Patau's Syndrome
Trisomy of Chromosome 13
• Extra fingers or toes (polydactyl)
• Deformed feet, known as rocker-bottom feet
• Neurological problems such as small head (microcephaly), failure of the brain to divide into halves during gestation (holoprosencephaly), severe mental deficiency
• Facial defects such as small eyes (microphthalmia), absent or malformed nose, cleft lip and/or cleft palate
• Heart defects (80% of individuals)
• Kidney defects
Edward's Syndrome
Trisomy of Chromosome 18
The extra chromosome is lethal for most babies born with this condition. It causes major physical abnormalities and severe mental retardation, and very few children afflicted with this disease survive beyond a year.
A third copy of chromosome 18 causes numerous abnormalities. Most children born with Edwards' syndrome appear weak and fragile, and they are often underweight. The head is unusually small and the back of the head is prominent. The ears are malformed and low-set, and the mouth and jaw are small. The baby may also have a cleft lip or cleft palate. Frequently, the hands are clenched into fists, and the index finger overlaps the other fingers. The child may have clubfeet and toes may be webbed or fused.
Numerous problems involving the internal organs may be present. Abnormalities often occur in the lungs and diaphragm (the muscle that controls breathing), and heart defects and blood vessel malformations are common. The child may also have malformed kidneys and abnormalities of the urogenital system.
Down Syndrome
Trisomy of Chromosome 21
This is a mild to severe form of mental retardation accompanied by distinctive physical traits. People with Down syndrome have an irregularity with autosome pair 21. In most cases, there is an extra chromosome (i.e., trisomy). Down syndrome individuals typically have short, stocky bodies with thick hands and feet. Their hands commonly have a simian crease, which is a crease in the palm that runs completely from one side of the hand to the other. In addition, they usually have broad, short heads with small low-set ears, small concave saddle-shaped or flattened noses, relatively large ridged tongues that roll over a protruding lower lip, low muscle tone, and loose joints.
Klinefelter Syndrome
Trisomy of 23rd Pair (XXY)
Having 2X and 1Y chromosome
Males inherit one or more extra X chromosomes--their genotype is XXY or more rarely XXXY, XXXXY, or XY/XXY mosaic. They characteristically have relatively high-pitched voices, asexual to feminine body contours as well as breast enlargement, and comparatively little facial and body hair. They are sterile or nearly so, and their testes and prostate gland are small. As a result, they produce relatively small amounts of testosterone. 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. Like metafemales (described above), many Klinefelter syndrome men are an inch or so above average height. They also are likely to be overweight. They usually have learning difficulties as children, especially with language and short-term memory.
Trisomy of 23rd Pair (XYY)
Having 1 X & 2 Y chromosomes
Males inherit an extra Y chromosome--their genotype is XYY. As adults, these "super-males" are usually tall (above 6 feet) and generally appear and act normal. However, they produce high levels of testosterone. During adolescence, they often are slender, have severe facial acne, and are poorly coordinated. They are usually fertile and lead ordinary lives as adults. Many, if not most, are unaware that they have a chromosomal abnormality.