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what is the cause of a miscarriage 50% of the time?

chromosomal abnormalities


when should you order a chromosome test?

- prenatal findings: fetus has a growth retardation, multiple congenital anomilies, or edema in the ultrasound.
- Infancy and childhood: multiple congenital anomalies, unusual facial features, short stature, mental retardation, learning or attentional difficulties
- adulthood: learning disabilities, infertility, history of recurrent pregnancy loss or stillbirths


what is the acronym used to aid physicians in looking for clues that may indicate chromosomal anomalies?

FBGD (funny bodies got disorders)

F: unusual Facial features from the parents
B: birth defects or variations in physical features
G: growth retardation (ie. microcephaly)
D: developmental problems (mental retardation, learning disabilities, attention disorders.


what are some features of Trisomy 21.

- down syndrome
- mostly due to nondisjuntion with chromosome 21, rarely ever a robertsonian translocation though (4%)
- seen in moms that are younger usually


what occurs in Trisomy 21 monosaicism?

- very rare (1-2%)
- some cells lost the extra 21 chromosome while other retained the trisomy so milder symptoms.


what is the FBGD for trisomy 21?

F - distinct eyes, face, and neck
B - a third have a heart defect (pig duct arteriosis doesn't close between the pulmonary artery and descending aorta). Some have intestinal defects.
D - differing degrees of mental retardation and premature growth.


what are some of the features of Trisomy 18?

- much more severe than Trisomy 21
- much more rare (1/7,500 vs 1/800 for DS)


what is the FBGD for trisomy 18?

F - microcephaly among many others
B - serious heart defects, kidney malformations, intestinal malformations
G - severe mental retardation. 95% don't survive past first year of life.


What are some features of trisomy 13?

- more rare than trisomy 18 (1/15,000 vs 1/7,500)
- involves chromosome which is an acrocentric chromosome so it is possible to get a robertsonian translocation.


what are the more common chromosome abnormalities that are alleviated due to mosaicism?

- Sex chromosome abnormaliites
- trisomy 21 and 16


what is the most common microdeletion and what does it result in?

- the 22q deletion that results in DiGeorge or velocardiofacial syndrome.


what is the most common chromosomal abnormality at the moment of conception?

turner syndrome and only 1% of them go on to be born.
- only one X chromosome mostly due to an egg being fertilized by a sperm that is missing an X or Y chromosome.


what are the features of turner syndrome?

short stature, ovarian failure, late onset of puberty.
- visual spatial perceptual problems.


what are the features of triple X?

- no physical features are apparent
- mild learning difficulties with slight psychiatric and behavioral problems
- women have early menopause, premature ovarian failure but otherwise normal fertility


what are the features of klinefelter syndrome?

(47, XXY)
- no physical deformations at birth
- small testes, adolescent breast development (increased risk of breast cancer).
- infertile.


what occurs at the 14th cell stage and who discovered this?

Lyon discovered that at the 14th cell stage each cell shuts own one of its C chromosomes randomly and permanently. Each subsequent daughter cell will have the same X inactivation present.