Updated: 10/18/2018

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 (18)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
Calculator

(M1.BC.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? Review Topic

QID: 106984
FIGURES:
1

Endocardial cushion defects

83%

(20/24)

2

Aberrant development of 3rd and 4th pharyngeal pouches

17%

(4/24)

3

Hypertrophic cardiomyopathy

0%

(0/24)

4

Cystic medial necrosis of the aorta

0%

(0/24)

5

Valvular obstruction due to cardiac rhabdomyomas

0%

(0/24)

M1

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PREFERRED RESPONSE 1
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(M1.BC.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? Review Topic

QID: 107012
FIGURES:
1

Meiotic nondisjunction resulting in trisomy of chromosome 13

11%

(2/19)

2

Meiotic nondisjunction resulting in trisomy of chromosome 18

84%

(16/19)

3

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

0%

(0/19)

4

Microdeletion of the short arm on chromosome 5

5%

(1/19)

5

Microdeletion of the long arm on chromosome 7

0%

(0/19)

M1

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PREFERRED RESPONSE 2

(M1.BC.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? Review Topic

QID: 106976
1

Triple marker test

0%

(0/18)

2

Quadruple marker test

17%

(3/18)

3

Integrated test

0%

(0/18)

4

Ultrasound

0%

(0/18)

5

Amniocentesis

78%

(14/18)

M1

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(M1.BC.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? Review Topic

QID: 106510
1

Fetus is normal, continue with pregnancy as expected

4%

(1/23)

2

Confirmatory amniocentesis and chromosomal analysis of the fetal cells

83%

(19/23)

3

Biopsy and pathologic examination of fetus

0%

(0/23)

4

Maternal karyotype

0%

(0/23)

5

Cell-free fetal DNA analysis

9%

(2/23)

M1

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PREFERRED RESPONSE 2

(M1.BC.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? Review Topic

QID: 106541
FIGURES:
1

Figure A

2%

(5/201)

2

Figure B

1%

(2/201)

3

Figure C

19%

(39/201)

4

Figure D

76%

(152/201)

5

Figure E

0%

(0/201)

M1

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PREFERRED RESPONSE 4

(M1.BC.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? Review Topic

QID: 106549
FIGURES:
1

Figure A

6%

(1/17)

2

Figure B

0%

(0/17)

3

Figure C

82%

(14/17)

4

Figure D

12%

(2/17)

5

Figure E

0%

(0/17)

M1

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PREFERRED RESPONSE 3

(M1.BC.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? Review Topic

QID: 106508
FIGURES:
1

Hypothyroidism

0%

(0/18)

2

Microdeletion on chromosome 22

0%

(0/18)

3

Maternal alcohol consumption during pregnancy

6%

(1/18)

4

Trisomy 18

0%

(0/18)

5

Trisomy 21

94%

(17/18)

M1

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PREFERRED RESPONSE 5

(M1.BC.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? Review Topic

QID: 106509
1

Increased AFP, normal HCG, normal unconjugated estriol

18%

(5/28)

2

Decreased AFP, increased HCG, decreased unconjugated estriol

57%

(16/28)

3

Decreased AFP, decreased HCG, decreased unconjugated estriol

14%

(4/28)

4

Normal AFP, increased HCG, decreased unconjugated estriol

4%

(1/28)

5

Normal AFP, decreased HCG, decreased unconjugated estriol

4%

(1/28)

M1

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PREFERRED RESPONSE 2

(M1.BC.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? Review Topic

QID: 106536
FIGURES:
1

Trisomy 21

32%

(10/31)

2

Trisomy 18

19%

(6/31)

3

Trinucleotide repeat expansion

0%

(0/31)

4

Partial deletion on chromosome 22

45%

(14/31)

5

Uniparental disomy

0%

(0/31)

M1

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PREFERRED RESPONSE 4

(M1.BC.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? Review Topic

QID: 107014
FIGURES:
1

Patau syndrome

85%

(22/26)

2

Edwards syndrome

8%

(2/26)

3

Down syndrome

0%

(0/26)

4

Turner syndrome

8%

(2/26)

5

Klinefelter syndrome

0%

(0/26)

M1

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PREFERRED RESPONSE 1

(M1.BC.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? Review Topic

QID: 106994
FIGURES:
1

Figure A

76%

(29/38)

2

Figure B

3%

(1/38)

3

Figure C

5%

(2/38)

4

Figure D

11%

(4/38)

5

Figure E

3%

(1/38)

M1

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PREFERRED RESPONSE 1
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