Lecture 26

Question 1

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

Answer 1

chromosomal abnormalities

Question 2

when should you order a chromosome test?

Answer 2

• 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

Question 3

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

Answer 3

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.

Question 4

what are some features of Trisomy 21.

Answer 4

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

Question 5

what occurs in Trisomy 21 monosaicism?

Answer 5

• very rare (1-2%)

- some cells lost the extra 21 chromosome while other retained the trisomy so milder symptoms.

Question 6

what is the FBGD for trisomy 21?

Answer 6

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.

Question 7

what are some of the features of Trisomy 18?

Answer 7

• much more severe than Trisomy 21

- much more rare (1/7,500 vs 1/800 for DS)

Question 8

what is the FBGD for trisomy 18?

Answer 8

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.

Question 9

What are some features of trisomy 13?

Answer 9

• 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.

Question 10

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

Answer 10

• Sex chromosome abnormaliites

- trisomy 21 and 16

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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.

Question 13

what are the features of turner syndrome?

Answer 13

short stature, ovarian failure, late onset of puberty.

- visual spatial perceptual problems.

Question 14

what are the features of triple X?

Answer 14

• 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

Question 15

what are the features of klinefelter syndrome?

Answer 15

(47, XXY)

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

Question 16

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

Answer 16

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.