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Trisomy 21 (Down Syndrome)
- 1. Extra copy of chromosome 21. In 75% of cases, occurs as a result of maternal (oocyte) nondisjunction.
- 2. Growth and mental retardation.
- 3. Craniofacial defects: brachycephaly, up-slanting palpebral fissures, medial epicanthial folds, small nose with low nasal bridge, small ears.
- 4. Cardiac defects in approximately 40% of cases: usually septal defects of PDA (patent ductus arteriosus).
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Trisomy 18 (Edward syndrome)
- 1. Extra copy of chromosome 18.
- 2. Mental retardation
- 3. Cardiac defects
- 4. Craniofacial: Low-set ears, micrognathia
- 5. Clenched fists: flexion of fingers, hands
- 6. Limited capacity for survival; only about 5-10% live to first year; only handful of case reports of children living to 10 years old.
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Trisomy 13 (Patau Syndrome)
- 1. Extra copy of chromosome 13.
- 2. Mental retardation;holoprosencephaly
- 3. Cardiac defects
- 4. Deafness
- 5. Craniofacial: Cleft-lip and palate, eye defects
- 6. Limited capacity for survival; usually only survive 7 days postnally.
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Trisomy 8 (Warkany Syndrome)
- 1. Extra copy of chromosome 8.
- 2. Mental retardation
- 3. Long, slender trunk
- 4. Craniofacial: Prominent forehead, strabismus, micrognathia, cleft palate.
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Klinefelter Syndrome; (47, XXY)
- 1. Extra copy of chromosome X.
- 2. Male;
- 3. presence of Barr bodies
- 4. Sterile, testicular atrophy
- 5. gynecomastia
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f. Turner's Syndrome (45, X)
- 1. One less copy of X chromosome.
- -In 80% of cases, paternal nondisjunction.
- 2. Only monosomy compatible with life.
- 3. Female
- 4. Short stature, broad chest, short neck
- 5. Congenital lymphedema of hands and feet
- 6. Streak gonads (gonadal dysgenesis)
- 7. Lack of secondary sex characteristic development at puberty
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Duplications of genes
the result of abnormal genetic crossovers. Duplication abnormalities are rare.
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define structural abnormalities
(deletions, microdeletions, duplications)
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Angelman Syndrome (Happy Puppet Syndrome)
- a.microDeletion on the long arm of chromosome 15.
- b. maternal chromosome.
- c. Mental retardation
- d. Puppet-like gait
- e. Absent speechProne to unprovoked periods of uncontrolled laughter
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Prader-Willi Syndrome
- a. microDeletion on the long arm of chromosome 15.
- b. paternal chromosome.
- c. Mental retardation
- d. Obesity and hypotonia
- e. Hypogonadism
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Miller-Dieker Syndrome
- a. Deletion short arm of chromosome 17 b. Lissencephaly (smooth brain), microcephaly
- c. Severe mental retardation
- d. Failure to thrive
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Microdeletions
- result from breakage and loss of only a few genes.
- a. Examples of microdeletions Angelman Syndrome (Happy Puppet Syndrome), Prader-Willi Syndrome, Miller-Dieker Syndrome
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Define Deletions
Breakage and loss of part of a chromosome (viruses, radiation, drugs, etc).
Examples of deletions 1. Cri-du-chat syndrome (deletion 5p syndrome) Deletion 4q syndrome
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Deletion 4q syndrome
- a. Partial deletion of the long arm of chromosome
- b. Growth and mental retardation, postnatal onset
- c. Cleft palate
- d. Limb abnormalities
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Cri-du-chat syndrome (deletion 5p syndrome)
- a. Partial deletion of the short arm of chromosome
- b. Characteristic cry of the cat sound due to malformation of larynx
- c. Growth retardation
- d. Mental retardation, microcephaly
- e. Cardiac defects
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Numerical Abnormalities
- Nondisjunction - chromosomes fail to separate during meiotic anaphase, resulting in aneuploidy.
- 2. The most common aneuploidies are trisomies (one extra copy) or monosomies (one less copy).
- 3. In women, rate of nondisjunction increases with age (example is for trisomy 21).
- 15-29 years: 1: 1500
- 30-34 years: 1: 800
- 35-39 years: 1: 270
- 40-44 years: 1: 100
- Over 45 years: 1: 50
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Triple X (47, XXX)
- 1. Extra copy of chromosome X.
- 2. Female; two Barr bodies in cells
- 3. Varying degrees of mental retardation
- 4. Amenorrheic
- 5. No classic pattern of malformation
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