Clinical Cytogenetics Chapter 6
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Questions and Answers

What is the primary cause of chromosomal disorders?

  • Absence of chromosomal material
  • Excess of chromosomal material
  • Abnormal rearrangements of chromosomes
  • All of the above (correct)

    • Which type of chromosomal imbalance is tolerated better?

  • Autosomal imbalance
  • Mitochondrial gene mutation
  • Triplet repeat mutation
  • Sex chromosomal imbalance (correct)

    • What is the characteristic of Trisomy 21 or Down Syndrome?

  • 47 chromosome count (correct)
  • Paternal origin
  • Meiotic nondisjunction
  • 46 chromosome count

    • What is the result of partial deletion of the short arm of chromosome 5?

    <p>Cri du chat syndrome</p> Signup and view all the answers

    Which of the following is a characteristic of autosomal disorders?

    <p>All of the above</p> Signup and view all the answers

    What is the consequence of loss of chromosomal material?

    <p>More severe defects than gain of chromosomal material</p> Signup and view all the answers

    What is the origin of the extra chromosome in Trisomy 21?

    <p>Maternal origin</p> Signup and view all the answers

    What is the characteristic of Turner syndrome in infancy?

    <p>Swelling of the nape of the neck due to distended lymphatic channels</p> Signup and view all the answers

    Which of the following disorders is associated with mutations in the SOX9 gene on chromosome 17q?

    <p>Camptomelic dysplasia</p> Signup and view all the answers

    What is the typical karyotype of individuals with female pseudohermaphroditism?

    <p>46,XX</p> Signup and view all the answers

    Which of the following diseases is caused by a triplet repeat mutation?

    <p>Myotonic dystrophy</p> Signup and view all the answers

    What is the characteristic of Fragile X syndrome in males?

    <p>Macroorchidism</p> Signup and view all the answers

    What is the typical inheritance pattern of Fragile X syndrome?

    <p>X-linked dominant</p> Signup and view all the answers

    What is the result of expression of a FMR1 gene bearing a permutation in some males and females?

    <p>Fragile X tremor/ataxia</p> Signup and view all the answers

    What is the characteristic cry of infants with Cri du Chat Syndrome?

    <p>A soft, mewing cry</p> Signup and view all the answers

    What is the genetic defect associated with 22q11.2 Deletion Syndrome?

    <p>A small interstitial deletion of band 11 on the long arm of chromosome 22</p> Signup and view all the answers

    What is the karyotype associated with Klinefelter Syndrome?

    <p>47,XXY</p> Signup and view all the answers

    What is the characteristic facial feature of Trisomy 13 Patau syndrome?

    <p>Microcephaly</p> Signup and view all the answers

    What is the primary immunological defect in 22q11.2 Deletion Syndrome?

    <p>T cell immunodeficiency</p> Signup and view all the answers

    What is the characteristic body habitus of individuals with Klinefelter Syndrome?

    <p>Eunuchoid body habitus</p> Signup and view all the answers

    What is the cardiac defect associated with 22q11.2 Deletion Syndrome?

    <p>All of the above</p> Signup and view all the answers

    What is the estimated incidence of trisomy 21 among liveborn children or fetuses of mothers 35 years of age or older?

    <p>1/800</p> Signup and view all the answers

    What is the characteristic facial feature of Down syndrome?

    <p>Flat nasal bridge</p> Signup and view all the answers

    What is the percentage of patients with trisomy 21 who are mosaics, having a mixture of 46- and 47-chromosome cells?

    <p>1%</p> Signup and view all the answers

    What is the most common type of chromosomal abnormality in Down syndrome?

    <p>Trisomy 21</p> Signup and view all the answers

    What is the estimated recurrence risk in families when a parent, especially the mother, is a carrier of a Robertsonian translocation?

    <p>High</p> Signup and view all the answers

    What is the characteristic feature of the hands in Down syndrome?

    <p>Single transverse palmar crease</p> Signup and view all the answers

    What is the estimated incidence of Trisomy 18 (Edwards Syndrome)?

    <p>1/5,000</p> Signup and view all the answers

    What is the characteristic heart defect in Trisomy 18 (Edwards Syndrome)?

    <p>All of the above</p> Signup and view all the answers

    What is the characteristic intellectual disability in Trisomy 18 (Edwards Syndrome)?

    <p>Severe intellectual disability</p> Signup and view all the answers

    Study Notes

    Cytogenetic Abnormalities

    • Chromosomal disorders associated with absence (deletion, monosomy), excess (trisomy), or abnormal rearrangements (translocations) of chromosomes
    • Loss of chromosomal material produces more severe defects than does a gain
    • Imbalances of sex chromosomes are tolerated much better than imbalances of autosomes

    Autosomal Disorders

    • Numerous rare chromosome disorders involving gain or loss of an entire chromosome or a chromosome segment
    • Three well-defined non-mosaic chromosome disorders compatible with postnatal survival
      • Trisomy 21 - Down Syndrome
      • Trisomy 18 - Edwards Syndrome
      • Trisomy 13 - Patau Syndrome

    Trisomy 21 - Down Syndrome

    • 95% of affected persons have trisomy 21, with a chromosome count of 47
    • Meiotic nondisjunction, mostly in maternal meiosis I
    • Characteristics:
      • Growth retardation
      • Mental retardation
      • Multiple congenital anomalies
      • Increased risk of developing acute leukemia and Alzheimer disease
    • 1/800 born with Down syndrome among liveborn children or fetuses of mothers 35 years of age or older

    Trisomy 18 - Edwards Syndrome

    • 1/5,000 live births
    • Characteristics:
      • Small head
      • Small jaw
      • Clenched fists with overlapping fingers
      • Severe intellectual disability
      • Kidney malformations
      • Structural heart defects at birth
      • Intestines protruding outside the body (omphalocele)
      • Esophageal atresia
    • Prognosis: Poor, with many cases resulting in spontaneous abortion or death in early childhood

    Trisomy 13 - Patau Syndrome

    • Characteristics:
      • Nervous system: Intellectual disability, motor disorder, microcephaly, holoprosencephaly, structural eye defects
      • Musculoskeletal and cutaneous: Polydactyly, low-set ears, prominent heel, deformed feet (rocker-bottom feet)
      • Urogenital: Abnormal genitalia, kidney defects
      • Heart defects: Ventricular septal defect, patent ductus arteriosus, dextrocardia, single umbilical artery

    Cri du Chat Syndrome

    • Deletion of part of the short arm of chromosome 5
    • Characteristics:
      • Microcephaly
      • Hypertelorism
      • Epicanthal folds
      • Low-set ears
      • Micrognathia
      • Crying infants with a mewing cat-like sound
      • 1% of institutionalized mentally retarded patients

    22q11.2 Deletion Syndrome - DiGeorge Syndrome

    • Small interstitial deletion of band 11 on the long arm of chromosome 22
    • Characteristics:
      • Congenital heart disease
      • Abnormalities of the palate
      • Facial dysmorphism
      • Developmental delay
      • Thymic hypoplasia with impaired T cell immunity
      • Parathyroid hypoplasia resulting in hypocalcemia
      • T cell immunodeficiency and hypocalcemia are the dominant features

    Sex Chromosomal Disorders

    • Klinefelter Syndrome:
      • 47,XXY karyotype
      • Male hypogonadism
      • Distinctive body habitus with an elongated body
      • Reduced facial, body, and pubic hair
      • Gynecomastia
      • Mental retardation
      • Increased risk of breast cancer and autoimmune diseases
    • Turner Syndrome:
      • 45,X karyotype
      • Primary hypogonadism in phenotypic females
      • Growth retardation
      • Abnormally short stature
      • Swelling of the nape of the neck
      • Cardiovascular abnormalities
      • Primary amenorrhea
      • Clinical hypothyroidism

    Disorders of Gonadal and Sexual Development

    • Hermaphroditism: Both ovarian and testicular tissue present
    • Gonadal Dysgenesis: Camptomelic dysplasia due to mutations in the SOX9 gene on chromosome 17q
    • Denys-Drash syndrome: Chromosomally male patients with ambiguous external genitalia
    • Frasier syndrome: Patients with XY complete gonadal dysgenesis
    • Female Pseudohermaphroditism: 46,XX karyotype with normal ovarian tissue but ambiguous or male external genitalia
    • Male Pseudohermaphroditism: 46,XY karyotype with incompletely masculinized or female external genitalia

    Single-Gene Disorders with Atypical Patterns of Inheritance

    • Fragile X Syndrome: Caused by a triplet repeat mutation, associated with autism-like symptoms, long face, and macroorchidism
    • Huntington Disease: Associated with neurodegenerative changes
    • Myotonic Dystrophy: Associated with neurodegenerative changes

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    Description

    This quiz covers clinical cytogenetics, specifically disorders of the autosomes and sex chromosomes, including gonadal and sexual development disorders. Based on Thompson & Thompson Genetics in Medicine, Chapter 6.

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