Chromosomal Disorders Flashcards
What is a marker chromosome
Small extra chromosome
What percentage of early pregnancy losses have chromosome abnormalities
50%
What type of chromosome abnormalities are most common in spontaneous abortions
Trisomies, 61%
What are prenatal features of trisomy 21, and what is the prenatal prognosis
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
What percent of babies with trisomy 21 will have anomalies on ultrasound
70%
What are clinical features of trisomy 13
Holoprosencephaly, median cleft lip/palate, cyclopia, proboscis, neural tube defects, omphalocele, polycystic kidneys, IUGR, poly or oligo hydramnios, polydactyl
What is the prognosis of trisomy 13
49% end in miscarriage or stillbirth, most die within ten days of birth, 90-95% by one year
Typically central apnea or cardiopulmonary arrest
What are clinical features of trisomy 18
Clenched hands with overlapping 4th digit, club or rocker bottom feet, heart defects, omphalocele, choroid plexus cysts, neural tube defects, IUGR, poly/oligo hydramnios
What is the prognosis of trisomy 18
72% end in miscarriage or stillbirth
Most die within ten days of birth, 90-95% in first year
Central apnea & cardiopulmonary common causes
What are the two types of triploidy
Diandric- two Sperm, 60%
Digynic- two eggs, 40%
What are ultrasound findings of diandric vs dygynic pregnancies
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
What is the recurrence risk for triploidy
1-1.5%
What is a molar pregnancy
Benign tumor in uterus, 46 chromosomes but all of paternal origin
What ultrasound findings are associated with monosomy x
Cystic hygroma, hydrops, congenital heart defects - coarctation of the aorta, bicuspid aortic valve, renal abnormalities
What is the prognosis for monosomy x
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
What chromosome difference is pallister killian syndrome
47, +i(12p) - isochromosome only present in fibroblast cells not in lymphocytes, level of mosaicism is highly variable
What tests can pick up pallister killian syndrome & which miss it
Amniocentesis & postnatal cell culture can pick up
CVS misses, blood karyotype is normal, not picked up on NIPT
What ultrasound findings are associated with pallister killian syndrome
Diaphragmatic hernia (40%), short femurs, polyhydramnios, congenital heart defects, other birth defects
What is the postnatal outlook for pallister killian syndrome
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
What percent of marker chromosomes are inherited
30%
What percent of mosaic results on amniocentesis reflect true mosaicism
60%
What heart defects are the most common heart defects associated with trisomy 21
Atrioventricular septal defect (endocardial cushion defect), ventricular septal defect, tetralogy of fallot
