Updated: 3/14/2021

Chromosomal Diseases

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Diseases Resulting from Autosomal Chromosome Abnormalities
  •  Down syndrome
    • most common chromosomal disorder
    • most common cause of congenital mental retardation
    • causes
      • trisomy 21 
        • nondisjunction (most common cause) 
          • occurs during anaphase of meiosis I
        • Robertsonian translocation 
        • mosaicism (least common cause)
    • presentation  
      • appearance
        • short stature
        • hypotonia
        • unique facial structure
          • epicanthic folds, macroglossia, flat profile, depressed nasal bridge
      • simian crease in palm
    • ↑ risk for
      • congenital heart disease
        • combined ASD and VSD
      • AML (< 3 y/o)
      • ALL (> 3 y/o) 
      • Alzheimer's disease
        • by 5th decade
        • due to amyloid precursor protein (APP) gene on 21
      • Hirschsprung's disease, duodenal atresia, congenital heart anamolies
        • atrioventricular canal is most common
        • endocardial cushion defects also very common
    • screening 
      • + quad screen  
        • ↓ α-fetoprotein
        • ↓ estriol
        • ↑ inhibin A
        • ↑ β-hCG
        • remember: high (hCG, inhibin); deficit (estriol, fetoprotein)
      • + ultrasound shows
        • high amount of fluid behind the neck
          • ↑ nuchal translucency
      • can confirm diagnosis with amniocentesis or chorionic villus sampling  
  • Edwards' syndrome 
    • most common trisomy resulting in live birth after Down syndrome
    • cause
      • trisomy 18  
        • nondisjunction
    • presentation
      • mental retardation
      • unique appearance 
        • rocker-bottom feet
        • micrognathia
          • small jaw
        • low-set ears
        • clenched hands with overlapping fingers
        • prominent occiput
      • congenital heart disease
        • VSD
    • death < 1 y/o
  • Patau's syndrome  
    • cause
      • trisomy 13
        • nondisjunction
    • presentation
      • mental retardation
      • unique appearance
        • microphthalmia
        • microcephaly
        • cleft lip/palate
        • holoprosencephaly 
        • polydactyly
      • VSD
      • cystic kidneys
    • death < 1 y/o
  • Cri-du-chat syndrome
    • cause
      • microdeletion of short arm of chromosome 5 
    • presentation
      • high-pitched crying/mewing
        • origin of name: French for cry-of-the-cat
      • microcephaly
      • moderate to severe mental retardation
      • epicanthal folds
      • VSD
  • Williams syndrome
    • cause
      • microdeletion of long arm of chromosome 7
        • region lost includes elastin gene
    • presentation
      • distinctive "elfin" facies
      • mental retardation
      • hypercalcemia
        • ↑ sensitivity to Vitamin D
      • unique behaviors
        • well-developed verbal skills
        • extreme friendliness with strangers
        • musical talent
      • supravalvular aortic stenosis
  • 22q11 microdeletions 
    • cause
      • microdeletion at chromosome 22q11
        • abnormal embryological development of 3rd and 4th pharyngeal pouch
    • variable pressenation
      • CATCH-22 disease
      • cleft palate
      • abnormal facies
      • T-cell deficiency
        • due to thymic aplasia
      • cardiac abnormalities
      • hypocalcemia
        • due to parathyroid aplasia
        • results in tetany
    • specific presentation of 22q11 microdeletions
      • DiGeorge syndrome 
        • defects in
          • thymus
          • parathyroid
          • heart
      • velocardiofacial syndrome
        • defects in
          • palate
          • face
          • heart
        • no abnormalities thymus, parathyroid

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Questions (19)
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(M1.BC.15.73) A 36-year-old pregnant woman undergoes a routine first-trimester pregnancy screen, which demonstrates decreased free B-hCG and decreased PAPP-A. Additionally, ultrasound shows increased nuchal translucency. A presumptive diagnosis is made based upon these findings and is later confirmed with genetic testing. The mother decides to carry the child to term, and, at birth, the child is noted to have cleft palate and polydactyly. The child is most likely to have which of the following karyotypes? Tested Concept

QID: 106549
FIGURES:
1

Figure A

7%

(2/30)

2

Figure B

10%

(3/30)

3

Figure C

67%

(20/30)

4

Figure D

17%

(5/30)

5

Figure E

0%

(0/30)

M 2 D

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(M1.BC.15.72) A 39-year-old pregnant woman at 16 weeks gestation recently underwent a quad-screen which revealed elevated beta-hCG, elevated inhibin A, decreased alpha-fetoprotein, and decreased estradiol. An ultrasound was performed which found increased nuchal translucency. Which of the following is recommended for diagnosis? Tested Concept

QID: 106510
1

Fetus is normal, continue with pregnancy as expected

3%

(1/37)

2

Confirmatory amniocentesis and chromosomal analysis of the fetal cells

86%

(32/37)

3

Biopsy and pathologic examination of fetus

0%

(0/37)

4

Maternal karyotype

0%

(0/37)

5

Cell-free fetal DNA analysis

8%

(3/37)

M 2 D

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(M1.BC.15.73) A 36-year-old G1P1 woman with no previous prenatal care or screening delivers a baby boy at 39 weeks gestation. On exam, you note micrognathia, microphthalmia, malformed low-set ears, rocker-bottom feet, and clenched hands with overlapping fingers. Which of the following karyotypes would you expect to find in this patient? Tested Concept

QID: 106541
FIGURES:
1

Figure A

2%

(5/226)

2

Figure B

1%

(2/226)

3

Figure C

19%

(43/226)

4

Figure D

75%

(170/226)

5

Figure E

0%

(0/226)

M 2 D

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(M1.BC.15.72) You are called to evaluate a newborn. The patient was born yesterday to a 39-year-old mother. You observe the findings illustrated in Figures A-C. What is the most likely mechanism responsible for these findings? Tested Concept

QID: 106508
FIGURES:
1

Hypothyroidism

0%

(0/27)

2

Microdeletion on chromosome 22

0%

(0/27)

3

Maternal alcohol consumption during pregnancy

4%

(1/27)

4

Trisomy 18

0%

(0/27)

5

Trisomy 21

96%

(26/27)

M 2 D

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(M1.BC.15.72) A 37-year-old woman presents for prenatal counseling at 18 weeks gestation. The patient tells you that her sister recently had a child with Down's syndrome, and the patient would like prenatal screening for Down's in her current pregnancy.

Which of the following prenatal screening tests and results would raise concern for Down's syndrome?
Tested Concept

QID: 106509
1

Increased AFP, normal HCG, normal unconjugated estriol

19%

(7/36)

2

Decreased AFP, increased HCG, decreased unconjugated estriol

58%

(21/36)

3

Decreased AFP, decreased HCG, decreased unconjugated estriol

11%

(4/36)

4

Normal AFP, increased HCG, decreased unconjugated estriol

6%

(2/36)

5

Normal AFP, decreased HCG, decreased unconjugated estriol

3%

(1/36)

M 2 C

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(M1.BC.15.72) You are called to examine a one-hour-old baby who was born with a facial defect illustrated in Figure A. The patient's ears appear to be low-set. On auscultation, there is a holosystolic murmur along the lower left sternal border. Basic labs return notable for hypocalcemia. What is the most likely underlying mechanism responsible for the abnormalities seen in this newborn? Tested Concept

QID: 106536
FIGURES:
1

Trisomy 21

24%

(10/41)

2

Trisomy 18

17%

(7/41)

3

Trinucleotide repeat expansion

0%

(0/41)

4

Partial deletion on chromosome 22

56%

(23/41)

5

Uniparental disomy

0%

(0/41)

M 1 D

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(M1.BC.14.1) A 39-year-old Caucasian female gives birth to a male child with the following physical characteristics: epicanthal folds, flat facial profile, a protruding tongue, and a characteristic finding on the palm (Figure A). Which of the following cardiovascular defect(s) is/are associated with the above presentation? Tested Concept

QID: 106984
FIGURES:
1

Endocardial cushion defects

87%

(27/31)

2

Aberrant development of 3rd and 4th pharyngeal pouches

13%

(4/31)

3

Hypertrophic cardiomyopathy

0%

(0/31)

4

Cystic medial necrosis of the aorta

0%

(0/31)

5

Valvular obstruction due to cardiac rhabdomyomas

0%

(0/31)

M 1 D

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(M1.BC.14.27) A 41-year-old Caucasian female gives birth to a male infant at 38 weeks of gestation. On physical exam, the infant has a small jaw, malformed, low set ears, clenched hands with overlapping fingers, a prominent occiput, and a foot abnormality (Figure A). Which of the following is the etiology of this presentation? Tested Concept

QID: 107012
FIGURES:
1

Meiotic nondisjunction resulting in trisomy of chromosome 13

14%

(4/29)

2

Meiotic nondisjunction resulting in trisomy of chromosome 18

83%

(24/29)

3

Meiotic nondisjunction resulting in an absence of a second sex chromsome 45,XO

0%

(0/29)

4

Microdeletion of the short arm on chromosome 5

3%

(1/29)

5

Microdeletion of the long arm on chromosome 7

0%

(0/29)

M 2 E

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(M1.BC.14.0) A 28-year-old G2P1 female is concerned that she may give birth to another child with Down syndrome. She states that she may not be able to take care of another child with this disorder. Which of the following tests can confirm the diagnosis of Down syndrome in utero? Tested Concept

QID: 106976
1

Triple marker test

3%

(1/33)

2

Quadruple marker test

24%

(8/33)

3

Integrated test

3%

(1/33)

4

Ultrasound

3%

(1/33)

5

Amniocentesis

64%

(21/33)

M 2 D

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(M1.BC.14.0) A 40-year-old G1P0 returns to her gynecologist for an amniocentesis after an abnormal quad screen. A chromosomal analysis demonstrated the following karyotype (Figure A). Which of the following syndromes does the fetus have? Tested Concept

QID: 107014
FIGURES:
1

Patau syndrome

84%

(32/38)

2

Edwards syndrome

5%

(2/38)

3

Down syndrome

0%

(0/38)

4

Turner syndrome

11%

(4/38)

5

Klinefelter syndrome

0%

(0/38)

M 2 E

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(M1.BC.14.7) A 41-year-old G2P1 woman who is 15 weeks pregnant visits her OB-GYN for a routine prenatal quad screen. The results show decreased serum alpha fetal protein (AFP) and estriol, and increased serum beta human chorionic gonadotropin (hCG) and inhibin A. Subsequent ultrasound demonstrates increased nuchal translucency. The physician performs an amniocentesis to confirm these positive findings. Which of the following karyotypes is to be expected if the amniocentesis confirms the result of the quad screen? Tested Concept

QID: 106994
FIGURES:
1

Figure A

80%

(35/44)

2

Figure B

2%

(1/44)

3

Figure C

5%

(2/44)

4

Figure D

9%

(4/44)

5

Figure E

2%

(1/44)

M 2 D

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