chapter 3, Prenatal Screening, Dx, and Tx

Question 1

cystic fibrosis

Answer 1

autosomal recessive. gene responsible for chloride channels. Almost all CF pts have chronic lung dx because of recurrent infections, leading to irreversible lung damage and strain on the right ventricle (cor pulmonale).

Question 2

thalassemia. hemolytic anemia that are caused by mutations that result in reduction in the synthesis of either __ or __ chains that make up hemoglobin molecule.

Answer 2

beta or alpha

Question 3

beta thalassemia

Answer 3

impairment of beta chain production that leads to an excess of alpha chains. these disorders typically dx several months after birth because the presence of beta chain is important only postnatally when it would normally replace the gamma chain as the major non alpha chain.

autosomal recessive disorder. because heterozygotes will have a mild hemolytic anemia and low MCV <80fl, they can be screened by getting a CBC. confirmation then made by hemoglobin electrophoresis which will show an increase in alpha:beta ratio. hemoglobin A2.

Question 4

Alpha thalassemia

Answer 4

chain is encoded by 4 alleles on 2 chromosomes. 2/4 mutations can occur cis or trans,

Question 5

cis

Answer 5

same chromosome

Question 6

trains

Answer 6

being on 2 different chromosomes.

Question 7

cis mutations seen more commonly in

Answer 7

southeast asian

Question 8

trans more commonly seen in

Answer 8

african americans.

Question 9

with alpha thalassemia, deletions or alterations of 2,3, or 4 genes cause an increasingly severe phenotype. however,

Answer 9

deletion of one allele has no clinical significance.

the most severe form of alpha thalassemia causes fetal hydrops and is incompatible with life.

Question 10

Hemoglobin H disease is..

Answer 10

due to deletion of 3 alpha globin genes, resulting in accumulation of excss beta chains in the red cell.

Question 11

alpha thalassemia trait has how many deletions?

Answer 11

2. it carries a milder phenotype with mainly a microcytic anemia and a normal hemoglobin electrophoresis.

Question 12

patients with only ___ gene deletion are silent carriers are usually have an mcv of less than 85fl.

Answer 12

one

Question 13

molecular testing is needed to determine the # of genes lost. sorting out whether patients are cis or trains is particularly important. when both partners have a cis mutation, their child has a __ chance of getting the most severe variant that usually results in fetal death

Answer 13

25%. if they both have the trains mutation, the child will end up with trans mutation as well, and primarily remain an asymptomatic carrier.

Question 14

components of 1st trimester screening

Answer 14

nuchal translucency, which is combined with pregnancy associated plasma protein A (PAPP-A) and b-hcg.

Question 15

trisomy 21 , or extra chromosome 21 is the most common cause of

Answer 15

down syndrome

Question 16

typical phenotype of down syndrome

Answer 16

short stature, classic facies, developmental delay, and mental retardation with iqs ranging from 40s to as high as 90s.

Question 17

what is quad screen, when is it done?

Answer 17

1.msafp
2. hcg
3. estriol
4.inhibinA
done between 15-20 weeks of gestation.

Question 18

sensitivity of 1st trimester screen

Answer 18

82%-87%

Question 19

sensitivity for quad screen alone

Answer 19

80%

Question 20

combination of these 2 tests

Answer 20

95% with screen positive rate off 5%.

Question 21

trisomy 18 aka edward syndrome

Answer 21

another common trisomy. trisomy 18 is lethal aneuploidy and nearly all neonates die in the first 2 years of life. associated with multiple congenital anomalies which are typically seen on US.

Question 22

edward syndrome associated with what on sono?

Answer 22

clenched fists, overlapping digits, rocker bottom feet. cardiac defects including ventricular septal defect (VSD) and tetralogy of fallot, omphalocele, congenital diaphragmatic hernia, neural tube defects, and choroid plexus cysts.

Question 23

trisomy 13 aka patau syndrome.

Answer 23

85% of these newborns will not live past the 1st year of life. comonly associated anomalies include holoprosencephaly, celeft lip and palate, cystic hygroma, single nostrile or absent nose, omphalocele, cardiac anomalies including hypoplastic left heart, and limb anomalies including clubfoot and clubhand, polydactyly, and overlapping fingers.

Question 24

45,X

Answer 24

turner syndrome

Question 25

47xxy

Answer 25

kleinfelter syndrome

Question 26

individuals affected by Turner syndrome are phenotypically female and of short stature. they experience

Answer 26

primary amenorrhea, sexual infantilism, webbed neck, low-set ears, low posterior hairline, epicanthal folds, wide carrying angle of the arms, sheild like chest, wide set nipples, short fourth metacarpal, renal anomalies, lymphedema of the extremities at birth, and cardiovascular anomalies, especially coarctation of the aorta.

Question 27

the only anomaly in turner syndrome commonly seen in ultrasound is

Answer 27

cystic hygroma.

Question 28

neural tube defects develop as a result of defective closure by week __ of development

Answer 28

week 4. (6 weeks gestational age by LMP dating)tt

Question 29

if ventricular wall fails to fuse, there is VSD.

Answer 29

IF NOT REPAIRED, CAN LEAD TO EISENMENGER PHYSIOLOGY, THAT IS, R VENTRICULAR HYPERTROPHY, PULMONARY HYPERTENSION, AND RIGHT TO LEFT SHUNT.

Question 30

tetrology of fallot

Answer 30

VSD with overriding aorta, pulmonary stenosis (or atresia), and right ventricular hypertrophy.

Question 31

downsyndrome has been associated with many US findings, most notably the echogenic intracardiac focus EIF. , at most, doubles the pretest odds. DS risk is 1:1,000 , pt will have an increased risk of

Answer 31

1:500 after finding the EIF.

Question 32

prenatal diagnostic test. there are currently 3 ways that fetal cells are obtained:

Answer 32

1. amniocentesis
2. cvs
3. percutaneous umbilical blood sampling (pubs)