Ch 6 (pp 103-111)
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Questions and Answers

Which of the following is the most common cause of Down syndrome?

  • Trisomy 18
  • Monosomy X
  • Trisomy 21 (correct)
  • Trisomy 13

    • What is the approximate frequency of Trisomy 21 in live births?

  • 1 in every 700 to 1000 live births (correct)
  • 1 in every 2000 to 3000 live births
  • 1 in every 100 to 200 live births
  • 1 in every 5000 to 6000 live births

    • What did the discovery in 1959 reveal about Down syndrome?

  • It is caused by a mutation in chromosome 13
  • It is caused by the presence of an extra copy of chromosome 21 (correct)
  • It is caused by a mutation in chromosome 18
  • It is caused by the absence of chromosome 21

    • Which term, previously used in literature, is considered inappropriate and pejorative for describing Down syndrome?

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

    What percentage of individuals with Down syndrome are born with structural heart defects?

    <p>40%</p> Signup and view all the answers

    What is the approximate survival rate for children with Down syndrome to age 5 years?

    <p>90%</p> Signup and view all the answers

    What is the risk of developing leukemia for individuals with Down syndrome, compared to the general population?

    <p>15 to 20 times higher</p> Signup and view all the answers

    What is the approximate percentage of trisomy 21 conceptions that are spontaneously aborted?

    <p>75%</p> Signup and view all the answers

    What is the percentage of cases of trisomy 21 caused by nondisjunction?

    <p>95%</p> Signup and view all the answers

    What is the percentage of individuals with Down syndrome who experience moderate to mild intellectual disability?

    <p>90%</p> Signup and view all the answers

    What is the approximate percentage of trisomy 21 cases where the extra chromosome is contributed by the mother?

    <p>90%</p> Signup and view all the answers

    What is the percentage of trisomy 21 live births that show mosaicism?

    <p>2% to 4%</p> Signup and view all the answers

    What is the recurrence risk for Down syndrome among mothers younger than 30 years?

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

    What is the approximate percentage of trisomy 21 cases caused by new mutations?

    <p>95%</p> Signup and view all the answers

    What percentage of females with Down syndrome fail to ovulate?

    <p>40%</p> Signup and view all the answers

    What percentage of trisomy 21 cases are contributed by the mother?

    <p>90%</p> Signup and view all the answers

    What is the primary reason for the prevalence of trisomies among older mothers?

    <p>Increase in nondisjunction</p> Signup and view all the answers

    What is the prevalence of Down syndrome for mothers over the age of 45?

    <p>Approximately 1/25</p> Signup and view all the answers

    Which syndrome is associated with a single X chromosome (45,X)?

    <p>Turner syndrome</p> Signup and view all the answers

    What is the most common cause of congenital heart defects in infants with Turner syndrome?

    <p>Obstructive lesions of the left side of the heart</p> Signup and view all the answers

    What is the growth pattern observed in girls with Turner syndrome?

    <p>Proportionate short stature and no adolescent growth spurt</p> Signup and view all the answers

    What can increase height in girls with Turner syndrome?

    <p>Growth hormone administration</p> Signup and view all the answers

    What is the prevalence of sex chromosome aneuploidy in males?

    <p>1 in 400</p> Signup and view all the answers

    What is the prevalence of sex chromosome aneuploidy in females?

    <p>1 in 650</p> Signup and view all the answers

    What is the mortality rate during the first year of life for trisomies of the 13th and 18th chromosomes?

    <p>Close to 90%</p> Signup and view all the answers

    What is the traditional care approach for children with serious prognosis?

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

    What is the evidence for a paternal age effect on nondisjunction in males?

    <p>Little evidence</p> Signup and view all the answers

    What proportion of Down syndrome children are born to mothers younger than 35 years of age?

    <p>Approximately three-fourths</p> Signup and view all the answers

    What is the prevalence of Trisomy 18 (Edwards syndrome) in live births?

    <p>1 per 6000 live births</p> Signup and view all the answers

    What is the prevalence of Trisomy 13 (Patau syndrome) in live births?

    <p>1 in 10,000 births</p> Signup and view all the answers

    What percentage of live-born infants with trisomy 13 die during the first year of life?

    <p>88%</p> Signup and view all the answers

    In Down syndrome, the extra 21st chromosome is contributed by the mother in what percentage of cases?

    <p>90%</p> Signup and view all the answers

    What is the most common autosomal aneuploidy?

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

    Which gene overexpression is linked to intellectual disability in Down syndrome?

    <p>DYRK1A</p> Signup and view all the answers

    Which gene causes Alzheimer's features in Down syndrome?

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

    What is the mortality rate for trisomy 18 within the first few weeks of life?

    <p>50%</p> Signup and view all the answers

    What is a distinctive feature of trisomy 18 (Edwards syndrome)?

    <p>Prenatal growth deficiency</p> Signup and view all the answers

    What is a distinctive malformation seen in trisomy 13 (Patau syndrome)?

    <p>Orofacial clefts</p> Signup and view all the answers

    What is the cause of high mortality in trisomy 13 and trisomy 18?

    <p>Congenital heart defects</p> Signup and view all the answers

    What has shown increased survival for trisomy 18 patients?

    <p>Technological intervention</p> Signup and view all the answers

    Which chromosome abnormality is most common in Turner syndrome patients?

    <p>45,X karyotype</p> Signup and view all the answers

    What is the estimated occurrence of the 45,X karyotype in conceptions?

    <p>1-2%</p> Signup and view all the answers

    In Turner syndrome, what is the cause of most cases of monosomy X?

    <p>Absence of a paternally derived sex chromosome</p> Signup and view all the answers

    What is the primary treatment for teenagers with Turner syndrome to promote the development of secondary sexual characteristics?

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

    What is a common physical characteristic that may aid in the diagnosis of Turner syndrome in newborns?

    <p>Neck webbing</p> Signup and view all the answers

    Which gene is identified to contribute to short stature in Turner syndrome?

    <p>SHOX gene</p> Signup and view all the answers

    What is the estimated occurrence of Klinefelter syndrome in male births?

    <p>1/500 to 1/1000</p> Signup and view all the answers

    What is a common physical characteristic of individuals with Klinefelter syndrome?

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

    What is the primary hormone therapy for individuals with Klinefelter syndrome to enhance secondary sex characteristics?

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

    In Klinefelter syndrome, what is the source of the extra X chromosome in about 50% of cases?

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

    What is the effect of mosaicism on the likelihood of viable sperm production in Klinefelter syndrome?

    <p>Increases the likelihood</p> Signup and view all the answers

    What is a potential risk associated with gynecomastia in individuals with Klinefelter syndrome?

    <p>Increased risk of breast cancer</p> Signup and view all the answers

    Study Notes

    Genetic Syndromes: Turner Syndrome and Klinefelter Syndrome

    • Turner syndrome is characterized by the absence of normal ovaries, leading to underdevelopment of secondary sexual characteristics and infertility in most cases.
    • Teenagers with Turner syndrome are treated with estrogen to promote the development of secondary sexual characteristics and prevent osteoporosis.
    • The diagnosis of Turner syndrome is often made in newborns, especially if there is noticeable neck webbing and heart defects.
    • The chromosome abnormalities in Turner syndrome patients are quite variable, with about 50% having a 45,X karyotype and 30-40% having mosaicism.
    • Most cases of monosomy X are caused by the absence of a paternally derived sex chromosome.
    • The 45,X karyotype is estimated to occur in 1-2% of conceptions, but Turner syndrome is seen in only about 1/2000 to 1/3000 live-born girls.
    • Molecular analysis has identified specific genes involved in the Turner syndrome phenotype, such as the SHOX gene, which contributes to short stature.
    • Klinefelter syndrome, associated with a 47,XXY karyotype, is seen in approximately 1/500 to 1/1000 male births.
    • Patients with Klinefelter syndrome tend to be taller than average, with small testes, low testosterone levels, and a predisposition for learning disabilities.
    • Gynecomastia is seen in approximately one-third of individuals with Klinefelter syndrome, leading to an increased risk of breast cancer.
    • The extra X chromosome in Klinefelter syndrome is derived maternally in about 50% of cases, and mosaicism increases the likelihood of viable sperm production.
    • Testosterone therapy, beginning in mid-adolescence, can enhance secondary sex characteristics and decrease the risk of osteoporosis in Klinefelter syndrome.

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    Description

    Test your knowledge of genetic syndromes with this quiz on Turner Syndrome and Klinefelter Syndrome. Learn about the characteristics, diagnosis, chromosome abnormalities, and treatment options for these conditions.

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