Chromosomal Disorders

Question 1

What is a marker chromosome

Answer 1

Small extra chromosome

Question 2

What percentage of early pregnancy losses have chromosome abnormalities

Answer 2

50%

Question 3

What type of chromosome abnormalities are most common in spontaneous abortions

Answer 3

Trisomies, 61%

Question 4

What are prenatal features of trisomy 21, and what is the prenatal prognosis

Answer 4

Increased nt or thickened nuchal fold, absent or hypoplastic nasal bones, double bubble sign, shortened long bones, brachycephaly, heart defects in 50%, ventriculomegaly
35% do not go to term

Question 5

What percent of babies with trisomy 21 will have anomalies on ultrasound

Answer 5

70%

Question 6

What are clinical features of trisomy 13

Answer 6

Holoprosencephaly, median cleft lip/palate, cyclopia, proboscis, neural tube defects, omphalocele, polycystic kidneys, IUGR, poly or oligo hydramnios, polydactyl

Question 7

What is the prognosis of trisomy 13

Answer 7

49% end in miscarriage or stillbirth, most die within ten days of birth, 90-95% by one year
Typically central apnea or cardiopulmonary arrest

Question 8

What are clinical features of trisomy 18

Answer 8

Clenched hands with overlapping 4th digit, club or rocker bottom feet, heart defects, omphalocele, choroid plexus cysts, neural tube defects, IUGR, poly/oligo hydramnios

Question 9

What is the prognosis of trisomy 18

Answer 9

72% end in miscarriage or stillbirth
Most die within ten days of birth, 90-95% in first year
Central apnea & cardiopulmonary common causes

Question 10

What are the two types of triploidy

Answer 10

Diandric- two Sperm, 60%

Digynic- two eggs, 40%

Question 11

What are ultrasound findings of diandric vs dygynic pregnancies

Answer 11

Diandric: early onset symmetric IUGR, abnormally large placenta
Digynic: early onset asymmetric IUGR with large fetal head , small to Normal placenta
Both: holoprosencephaly, isolated ventriculomegaly, Arnold Chiari with spina bifida, dandy walker, nuchal thickening, heart defect, hydrops, renal, micrognathia, omphalocele, limb defects, oligo hydramnios

Question 12

What is the recurrence risk for triploidy

Answer 12

1-1.5%

Question 13

What is a molar pregnancy

Answer 13

Benign tumor in uterus, 46 chromosomes but all of paternal origin

Question 14

What ultrasound findings are associated with monosomy x

Answer 14

Cystic hygroma, hydrops, congenital heart defects - coarctation of the aorta, bicuspid aortic valve, renal abnormalities

Question 15

What is the prognosis for monosomy x

Answer 15

Prenatal: 99% SAB, 65% loss rate from 12-40 weeks
Postnatal: increased risk for early death from heart defects, if survive infancy usually reach adulthood, usually typical intelligent may have learning disabilities or behavioral concerns, almost always infertile, short stature, hormone replacement therapy for sexual characteristics

Question 16

What chromosome difference is pallister killian syndrome

Answer 16

47, +i(12p) - isochromosome only present in fibroblast cells not in lymphocytes, level of mosaicism is highly variable

Question 17

What tests can pick up pallister killian syndrome & which miss it

Answer 17

Amniocentesis & postnatal cell culture can pick up

CVS misses, blood karyotype is normal, not picked up on NIPT

Question 18

What ultrasound findings are associated with pallister killian syndrome

Answer 18

Diaphragmatic hernia (40%), short femurs, polyhydramnios, congenital heart defects, other birth defects

Question 19

What is the postnatal outlook for pallister killian syndrome

Answer 19

Profound ID, seizures, dysmorphic facies, streak of hypopigmentation, sparse hair, significant hypotonia, limited or absent speech, effects of diaphragmatic hernia
Some milder cases may be under reported

Question 20

What percent of marker chromosomes are inherited

Answer 20

30%

Question 21

What percent of mosaic results on amniocentesis reflect true mosaicism

Answer 21

60%

Question 22

What heart defects are the most common heart defects associated with trisomy 21

Answer 22

Atrioventricular septal defect (endocardial cushion defect), ventricular septal defect, tetralogy of fallot