52 Questions
Which of the following is the most common cause of Down syndrome?
Trisomy 21
What is the approximate frequency of Trisomy 21 in live births?
1 in every 700 to 1000 live births
What did the discovery in 1959 reveal about Down syndrome?
It is caused by the presence of an extra copy of chromosome 21
Which term, previously used in literature, is considered inappropriate and pejorative for describing Down syndrome?
Mongolism
What percentage of individuals with Down syndrome are born with structural heart defects?
40%
What is the approximate survival rate for children with Down syndrome to age 5 years?
90%
What is the risk of developing leukemia for individuals with Down syndrome, compared to the general population?
15 to 20 times higher
What is the approximate percentage of trisomy 21 conceptions that are spontaneously aborted?
75%
What is the percentage of cases of trisomy 21 caused by nondisjunction?
95%
What is the percentage of individuals with Down syndrome who experience moderate to mild intellectual disability?
90%
What is the approximate percentage of trisomy 21 cases where the extra chromosome is contributed by the mother?
90%
What is the percentage of trisomy 21 live births that show mosaicism?
2% to 4%
What is the recurrence risk for Down syndrome among mothers younger than 30 years?
1%
What is the approximate percentage of trisomy 21 cases caused by new mutations?
95%
What percentage of females with Down syndrome fail to ovulate?
40%
What percentage of trisomy 21 cases are contributed by the mother?
90%
What is the primary reason for the prevalence of trisomies among older mothers?
Increase in nondisjunction
What is the prevalence of Down syndrome for mothers over the age of 45?
Approximately 1/25
Which syndrome is associated with a single X chromosome (45,X)?
Turner syndrome
What is the most common cause of congenital heart defects in infants with Turner syndrome?
Obstructive lesions of the left side of the heart
What is the growth pattern observed in girls with Turner syndrome?
Proportionate short stature and no adolescent growth spurt
What can increase height in girls with Turner syndrome?
Growth hormone administration
What is the prevalence of sex chromosome aneuploidy in males?
1 in 400
What is the prevalence of sex chromosome aneuploidy in females?
1 in 650
What is the mortality rate during the first year of life for trisomies of the 13th and 18th chromosomes?
Close to 90%
What is the traditional care approach for children with serious prognosis?
Noninterventionist
What is the evidence for a paternal age effect on nondisjunction in males?
Little evidence
What proportion of Down syndrome children are born to mothers younger than 35 years of age?
Approximately three-fourths
What is the prevalence of Trisomy 18 (Edwards syndrome) in live births?
1 per 6000 live births
What is the prevalence of Trisomy 13 (Patau syndrome) in live births?
1 in 10,000 births
What percentage of live-born infants with trisomy 13 die during the first year of life?
88%
In Down syndrome, the extra 21st chromosome is contributed by the mother in what percentage of cases?
90%
What is the most common autosomal aneuploidy?
Trisomy 21
Which gene overexpression is linked to intellectual disability in Down syndrome?
DYRK1A
Which gene causes Alzheimer's features in Down syndrome?
APP
What is the mortality rate for trisomy 18 within the first few weeks of life?
50%
What is a distinctive feature of trisomy 18 (Edwards syndrome)?
Prenatal growth deficiency
What is a distinctive malformation seen in trisomy 13 (Patau syndrome)?
Orofacial clefts
What is the cause of high mortality in trisomy 13 and trisomy 18?
Congenital heart defects
What has shown increased survival for trisomy 18 patients?
Technological intervention
Which chromosome abnormality is most common in Turner syndrome patients?
45,X karyotype
What is the estimated occurrence of the 45,X karyotype in conceptions?
1-2%
In Turner syndrome, what is the cause of most cases of monosomy X?
Absence of a paternally derived sex chromosome
What is the primary treatment for teenagers with Turner syndrome to promote the development of secondary sexual characteristics?
Estrogen
What is a common physical characteristic that may aid in the diagnosis of Turner syndrome in newborns?
Neck webbing
Which gene is identified to contribute to short stature in Turner syndrome?
SHOX gene
What is the estimated occurrence of Klinefelter syndrome in male births?
1/500 to 1/1000
What is a common physical characteristic of individuals with Klinefelter syndrome?
Gynecomastia
What is the primary hormone therapy for individuals with Klinefelter syndrome to enhance secondary sex characteristics?
Testosterone
In Klinefelter syndrome, what is the source of the extra X chromosome in about 50% of cases?
Maternal derivation
What is the effect of mosaicism on the likelihood of viable sperm production in Klinefelter syndrome?
Increases the likelihood
What is a potential risk associated with gynecomastia in individuals with Klinefelter syndrome?
Increased risk of breast cancer
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.
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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