Chapter review
Bring the chapter together
Start with the case synthesis, answered in 3 separate parts, then work through mixed case-based questions. Every answer explains the clue that matters and why the closest alternative fails.
Case synthesis
Bringing it together: will it happen again?
A 26-year-old woman's second child, a boy, has upslanting palpebral fissures, a flat facial profile, a single palmar crease and bilious vomiting on day 1; the abdominal x-ray shows a double bubble. His karyotype is 46,XY,der(14;21)(q10;q10),+21. Their first child is healthy, and both parents are well. They ask whether it will happen again.
1. Why he is affected
How does he have Down syndrome with 46 chromosomes?
2. Where it came from
Which finding in the parents would make the recurrence risk high?
3. Risk and next step
The mother is the carrier. What should the couple be told?
Mixed case review
Morphology, mechanism and application. Some items need two sections at once.
- Q1Recurrence: free trisomy vs 21;21 translocationConnects 5.2 + 5.6L5 p.7, 10
Two healthy couples each have a child with Down syndrome. Child A is 47,XY,+21. Child B is 46,XX,+21,der(21;21)(q10;q10), and her mother's karyotype is 45,XX,der(21;21)(q10;q10).
What is the risk of Down syndrome in each couple's next live-born child?
- Q2Mitochondrial vs X-linked transmissionConnects 5.1 + 5.3L5 p.21
A 21-year-old man loses central vision in one eye and, two months later, in the other. His maternal uncle had the same illness at 24. He has two young daughters.
What is the risk that his daughters inherit the causative mutation from him?
- Q3Fragile X: maternal expansionConnects 5.1 + 5.3L5 p.19
A healthy 40-year-old man carries an FMR1 premutation of 90 CGG repeats.
Which statement about his children is correct?
- Q4Testing for UPDConnects 5.3 + 5.6L5 p.23, 34
A hypotonic newborn with poor suck is suspected of Prader–Willi syndrome. FISH for a 15q11–q13 deletion is normal.
Which test is best next?
- Q5CF: fat-soluble vitamin deficiencyConnects 5.1Ch. V cases p.5
A 6-year-old with cystic fibrosis who stopped taking his enzymes and vitamins has nosebleeds and easy bruising. PT is prolonged; platelets are normal.
What explains the bleeding?
- Q6Hypergonadotropic hypogonadismConnects 5.2 + 5.4L5 p.14, 16
Which laboratory finding do Turner syndrome and Klinefelter syndrome share?
- Q7Primary amenorrhea: Turner vs AISConnects 5.2 + 5.4L5 p.14, 24
Two 16-year-olds have primary amenorrhea. Patient 1 is short with a webbed neck and no breast development; ultrasound shows a uterus. Patient 2 is tall with well-developed breasts, scant pubic hair and no uterus.
Which pair of karyotypes is most likely?
- Q8Maternal diabetes: timing of effectsConnects 5.4 + 5.5L5 p.25, 28
Two women have diabetes in pregnancy. Woman A has type 1 diabetes with an HbA1c of 11% at conception. Woman B develops gestational diabetes at 26 weeks.
Which outcome is a risk mainly for woman A's baby?
- Q9Maternal PKUConnects 5.1 + 5.5Ch. V cases p.6–7
A 27-year-old woman with PKU stopped her diet as a teenager. Her son, whose father does not carry a PAH mutation, is born with microcephaly and a VSD and later has intellectual disability.
What is the cause of the child's problems?
- Q10Anticipation: parent of originConnects 5.1 + 5.3L5 p.3
A 14-year-old develops rigidity, seizures and school failure. His father developed chorea at 44.
Why did he develop Huntington disease so much earlier than his father?
- Q1122q11.2 deletion: diagnosisConnects 5.2 + 5.6L5 p.34
A 3-day-old has carpopedal spasm (calcium 6.1 mg/dL), a truncus arteriosus and a cleft palate. A chest film shows no thymic shadow. The karyotype is 46,XY.
Which test will most likely confirm the cause?
- Q12Congenital varicellaConnects 5.4 + 5.5L5 p.26
A newborn has a hypoplastic left leg, zigzag scars along one dermatome of the trunk, and chorioretinitis. The mother had chickenpox at 13 weeks.
Which statement is correct?
- Q13Nondisjunction → trisomy rescue → UPDConnects 5.2 + 5.3 + 5.6L5 p.8, 23
CVS at 11 weeks for a 41-year-old shows trisomy 15 in placental cells. The baby is born 46,XX, floppy and feeding poorly, and later becomes hyperphagic.
What happened?
- Q14Skewed X inactivationConnects 5.1 + 5.2L5 p.6
A 30-year-old woman whose brother has hemophilia A bleeds heavily after a tooth extraction. Her factor VIII activity is 30%.
What best explains her bleeding?
- Q15Diabetic pregnancy and RDSConnects 5.4 + 5.6L5 p.25, 32
A 4.3-kg boy is born at 37 weeks to a mother with poorly controlled gestational diabetes. Within hours he is grunting and retracting; glucose is 30 mg/dL.
Why is he at risk of respiratory distress despite being near term?
- Q16Germline + somatic: two-hit modelConnects 5.1L5 p.2
A 2-year-old has retinoblastomas in both eyes. His father had one eye removed in infancy for the same tumor.
Which statement best explains this family?
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Timed practice