chapter 3, Prenatal Screening, Dx, and Tx Flashcards
cystic fibrosis
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).
thalassemia. hemolytic anemia that are caused by mutations that result in reduction in the synthesis of either __ or __ chains that make up hemoglobin molecule.
beta or alpha
beta thalassemia
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.
Alpha thalassemia
chain is encoded by 4 alleles on 2 chromosomes. 2/4 mutations can occur cis or trans,
cis
same chromosome
trains
being on 2 different chromosomes.
cis mutations seen more commonly in
southeast asian
trans more commonly seen in
african americans.
with alpha thalassemia, deletions or alterations of 2,3, or 4 genes cause an increasingly severe phenotype. however,
deletion of one allele has no clinical significance.
the most severe form of alpha thalassemia causes fetal hydrops and is incompatible with life.
Hemoglobin H disease is..
due to deletion of 3 alpha globin genes, resulting in accumulation of excss beta chains in the red cell.
alpha thalassemia trait has how many deletions?
- it carries a milder phenotype with mainly a microcytic anemia and a normal hemoglobin electrophoresis.
patients with only ___ gene deletion are silent carriers are usually have an mcv of less than 85fl.
one
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
25%. if they both have the trains mutation, the child will end up with trans mutation as well, and primarily remain an asymptomatic carrier.
components of 1st trimester screening
nuchal translucency, which is combined with pregnancy associated plasma protein A (PAPP-A) and b-hcg.
trisomy 21 , or extra chromosome 21 is the most common cause of
down syndrome
typical phenotype of down syndrome
short stature, classic facies, developmental delay, and mental retardation with iqs ranging from 40s to as high as 90s.
what is quad screen, when is it done?
1.msafp
2. hcg
3. estriol
4.inhibinA
done between 15-20 weeks of gestation.
sensitivity of 1st trimester screen
82%-87%
sensitivity for quad screen alone
80%
combination of these 2 tests
95% with screen positive rate off 5%.
trisomy 18 aka edward syndrome
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.
edward syndrome associated with what on sono?
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.
trisomy 13 aka patau syndrome.
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.
45,X
turner syndrome
47xxy
kleinfelter syndrome
individuals affected by Turner syndrome are phenotypically female and of short stature. they experience
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.
the only anomaly in turner syndrome commonly seen in ultrasound is
cystic hygroma.
neural tube defects develop as a result of defective closure by week __ of development
week 4. (6 weeks gestational age by LMP dating)tt
if ventricular wall fails to fuse, there is VSD.
IF NOT REPAIRED, CAN LEAD TO EISENMENGER PHYSIOLOGY, THAT IS, R VENTRICULAR HYPERTROPHY, PULMONARY HYPERTENSION, AND RIGHT TO LEFT SHUNT.
tetrology of fallot
VSD with overriding aorta, pulmonary stenosis (or atresia), and right ventricular hypertrophy.
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
1:500 after finding the EIF.
prenatal diagnostic test. there are currently 3 ways that fetal cells are obtained:
- amniocentesis
- cvs
- percutaneous umbilical blood sampling (pubs)
