Abnormalities of chromosome number Flashcards by Kristine Udnæseth

What is polyploidy?

The presence of a complete set of extra chromosomes in a cell

Commonly seen in plants and occasionally in humans

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What are euploid cells?

Cells that contain a multiple of 23 chromosomes

Includes haploid gametes and diploid somatic cells

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What are the karyotypes for triploidy and tetraploidy in humans?

Triploidy: 69,XXX; Tetraploidy: 92,XXXX

Assumes all sex chromosomes are X

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What is the most common cause of triploidy?

Fertilization of an egg by two sperm (dispermy)

Can also result from fusion of an ovum and a polar body

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What is the frequency of triploidy in live births?

About 1 in 10,000 live births

Accounts for an estimated 15% of chromosome abnormalities at conception

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What is aneuploidy?

Cells that contain missing or additional individual chromosomes

Not a multiple of 23 chromosomes

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What are the two main types of aneuploidies?

Monosomy and trisomy

Monosomy: one copy of a chromosome; Trisomy: three copies of a chromosome

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What is the most common cause of aneuploidy?

Nondisjunction during meiosis

Can occur in meiosis I or II

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What is Trisomy 21 commonly known as?

Down syndrome

Most common autosomal aneuploid condition compatible with survival

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What are the characteristic facial features of Down syndrome?

Depressed nasal root, upslanting palpebral fissures, overfolded ears, flattened maxillary region

Other features include short neck and round cheeks

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What percentage of individuals with Down syndrome have congenital heart defects?

Approximately 40%

Most common defect is an atrioventricular (AV) canal

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

More than 90%

Significant improvements due to medical advancements

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

About 1%

This is 10 times higher than the population risk for this age group

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What is the typical IQ range for individuals with Down syndrome?

Standardized IQ ranging from 40 to 60

Accounts for about 10% of all cases of intellectual disability in the U.S.

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What is the role of the DYRK1A gene in Down syndrome?

Candidate for intellectual disability when overexpressed

Affects learning and memory

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What is mosaicism in the context of Down syndrome?

Presence of some normal somatic cells and some cells with trisomy 21

Seen in approximately 2% to 4% of trisomy 21 live births

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What is the significance of maternal age in Down syndrome cases?

Stronger correlation with increased risk of producing a child with Down syndrome

About 75% of maternal nondisjunction occurs during meiosis I

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What is the common medical problem related to hearing in children with Down syndrome?

Conductive and sensorineural hearing loss

Routine hearing tests recommended

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Fill in the blank: The extra chromosome in Down syndrome is contributed by the ________ in approximately 90% of cases.

mother

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True or False: All cases of trisomy 21 result from maternal nondisjunction.

False

Some cases are caused by chromosome translocations

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What is the recommended follow-up for hypothyroidism in children with Down syndrome?

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Thyroid hormone levels should be measured annually starting at one year of age

Confirm normal newborn screening first

What types of hearing loss are seen in children with Down syndrome?

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Sensorineural and conductive hearing loss

Routine hearing tests are recommended at birth and every 6 months until 2 years of age.

What is a common condition in persons with Down syndrome?

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Obstructive sleep apnea (OSA)

Referral to a sleep disorder clinic or pulmonologist is recommended before 4 years of age.

What is an important component of routine care for infants and children with Down syndrome?

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Referral to preschool programs for developmental disabilities intervention

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

About 1 per 6000 live births ## Footnote It is much more common at conception and among stillborns.

What are characteristic features of infants with Trisomy 18?

Prenatal growth deficiency, characteristic facial features, distinctive hand abnormality ## Footnote Minor anomalies include small ears, small mouth, short sternum, and short halluces.

What percentage of children with Trisomy 18 have congenital heart defects?

90% ## Footnote VSDs with dysplasia of multiple heart valves are most common.

What is the mortality rate for infants with Trisomy 18 within the first year?

5% to 8% survival ## Footnote About 50% die within the first few weeks of life.

What developmental abilities are seen in children with Trisomy 18?

Marked developmental disabilities; most do not walk independently, but some learn communication skills ## Footnote Some older children may walk unassisted.

What is the survival rate for children with Trisomy 13 (Patau syndrome)?

About 88% of live-born infants die during the first year of life

What are common malformations associated with Trisomy 13?

Orofacial clefts, microphthalmia, postaxial polydactyly, heart defects, renal abnormalities ## Footnote Cutis aplasia can also be a diagnostic clue.

What is the maternal age effect observed in trisomies?

Risk of trisomy increases with maternal age ## Footnote Less than 1/1000 risk under 30 years, increasing to 1/25 after 45 years.

What is the primary cause of increased trisomy prevalence in older mothers?

Nondisjunction during meiosis

What is the prevalence of sex chromosome aneuploidy among live-born infants?

About 1 in 400 males and 1 in 650 females

What is Turner syndrome characterized by?

Single X chromosome (45,X), short stature, sexual infantilism, ovarian dysgenesis ## Footnote Physical features include a triangle-shaped face and broad webbed neck.

What treatment is commonly administered to girls with Turner syndrome to promote secondary sexual characteristics?

Estrogen therapy

What percentage of individuals with Turner syndrome have congenital heart defects?

About 50%

True or False: Maternal age is the only known correlated factor affecting nondisjunction in humans.

True

What is the prevalence of Down syndrome in relation to maternal age?

Increases with maternal age, especially after 35 years ## Footnote Data shows a significant rise in prevalence for mothers aged 35 and older.

What are the common indicators for diagnosing Turner syndrome in newborns?

Webbing of the neck and heart defects ## Footnote These physical clues can lead to early diagnosis.

What percentage of Turner syndrome patients have a 45,X karyotype?

About 50% ## Footnote This karyotype is significant in the diagnosis of Turner syndrome.

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

1% to 2% ## Footnote Despite this occurrence, Turner syndrome is rare among live births.

What gene mutation is associated with short stature in Turner syndrome?

SHOX gene ## Footnote This gene plays a key role in limb development and is affected in Turner syndrome.

What is the typical karyotype for most females with Turner syndrome?

45,X ## Footnote This condition is commonly associated with high rates of spontaneous abortion.

What is the karyotype associated with Klinefelter syndrome?

47,XXY ## Footnote This chromosomal arrangement leads to various physical and developmental characteristics.

What are common physical features of Klinefelter syndrome?

Tall stature, small testes, gynecomastia ## Footnote These features often manifest post-puberty.

What hormone therapy is recommended for males with Klinefelter syndrome?

Testosterone therapy ## Footnote This therapy helps in developing secondary sexual characteristics and improves psychological well-being.

What is the incidence of 47,XXX karyotype in females?

Approximately 1/1000 ## Footnote This condition typically has benign effects but may include sterility or mild cognitive disabilities.

What behavioral issues are more common in males with 47,XYY syndrome?

Minor behavioral disorders, hyperactivity, attention deficit disorder ## Footnote These issues are more prevalent, but violent criminal behavior is not associated with this karyotype.

What type of genetic crossover can lead to XX males?

Faulty crossover between the X and Y chromosomes ## Footnote This can result in XX males having the SRY gene, leading to male phenotype despite a female karyotype.

Abnormalities of chromosome number Flashcards

(50 cards)