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Genetics > Clinical cytogenetics > Flashcards

Clinical cytogenetics Flashcards

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1
Q

3 well defined non mosaic autosomal trisomies

A

Trisomy 21-Downs syndrome
Trisomy 18, Trisomy 13.
Somewhat tolerated by body so we will see live born infants . . . No other chromosome trisomies would tolerate life

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2
Q

Autosomal disorders

A

Can be either TRISOMIES OR MONOSOMIES

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3
Q

Down syndrome

A

most common chrome disorder and cause for moderate mental retardation.*Atrioventricular septal defect. Simian crease, clinodactyly, congential Heart disease,duodenal atresia, and tracheoesophageal fistula, premature dementia w/ features of alzheimers. Hypotonia, short,brachycephaly,flat occiput, flat nasal bridge with low set ears,Burshfield spots around iris, epicanthal folds

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4
Q

Chromosomes in Down syndrome: True Trisomy 21

A

95% due to meiotic nondisjunction
4% Robertsonian translocation 21q and chromosome 14 or 22. no relation to maternal age, high risk of recurrence in families.
21q21q translocation-> isochormosome: can’t have normal children, 1% recurrence risk, greater for mothers over 30

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5
Q

Mosaic down syndrome

A

rare

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6
Q

Partial trisomy

A

very rare; only part of q arm of chromosome 21 in triplicate. A down syndrome patient with no cytogenetically visible chromosome abnormalities.

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7
Q

Trisomy 18-Edward Syndrome-phenotype

A

*Fist clench of 2nd and 5th digits overlapping 3 and 4th, ears low set and malformed, head with prominent occiput, jaw recedes, Rocker-bottom feet, hypo plastic nails, mental retardation, severe malfomation of heart

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8
Q

Trisomy 18

A

Increased maternal age. exists in translocation and mosaic form. 95% of conceptuses are spontaneously aborted.Usually do not survive more than a few months.

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9
Q

Trisomy 13-Patau Syndrome phenotype

A

Cleft lip and palate, occular abns, microcephaly and wide open suture, congential heart and urogenital defects, severe central nervous system, rocker-bottom feet, clenched fist, simian crease, mental retardation, microphthalmia, iris coloboma, post axial polydactyly, sloping forehead and malformed ears

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10
Q

Trisomy 13

A

increased maternal age, usually nondisjunction, recurrence <2%.

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11
Q

Full monosomies cannot be tolerated, but

A

there are some partial monosomies,

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12
Q

Autosomal deletion syndromes

A

cytogenetically visible autosomal deletions occur with an incidence of 1/7000.
Ex. Cri du Chat

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13
Q

Cri Du Chat Syndrome

A

Large deletion in chromosome 5p. del5p15.3. 1% of institutionalized mentally retarded. 10-15% are offspring of translocation carriers.
Haploinsufficiency of genes within band 5p15.2

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14
Q

Cri Du Chat phenotype

A

Microcephaly, hypertelorism-wide bridge of nose, wide spaced eyes; severe mental retardation, epicanthal folds, low set ears, micrognathia, heart defects

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15
Q

Microdeletion syndromes

A

Segmental aneusomy->small deletions. Contiguous gene syndrome:haploinsufficiency of multiple contiguous genes.
Ex.Charcot-Marie-Tooth, DiGeorge syndrome
Cannot be seen under normal microscope-use high resol like FISH.

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16
Q

DiGeorge Syndrome or Velocardiofacial Syndrome

A

AD Microdeletion in chromosome 22q11.2.

common,mediated by homologous recombination b/w low copy repeated seqs.

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17
Q

DiGeorge Syndrome or Velocardiofacial Syndrome-Phenotype

CATCH-22

A

Heart defects-5% of all congenital heart defects.
40% of patients with tetralogy of Fallot and Pulmonary atresia.
60% with tetralogy of Fallot and absent pulmonary valve.
Craniofacial anomalies, mental retardation
Cardiac
Abnormal facies
Thymic hypoplasia
Cleft palate
Hypocalcemia

18
Q

Tetralogy of Fallot:

A
  1. Ventricular septal defect b/w right and left ventricles
  2. narrowing of pulmonary outflow tract
  3. Overriding aorta that is shifted over the right ventricle and ventricular septal defect, instead of coming out only from the left ventricle
  4. Thickened wall of the right ventricle (right ventricular hypertrophy)
19
Q

Sex chromosomes,X and Y play role in primary(gonadal) sex

A

X and Y pair during meiosis I -> pseudoautosomal region. Y encodes for less than 50 genes

20
Q

Embryology of the reproductive system

A

6th wk both sexes form primitive gonads.
Default developmental pathway -> ovarian
TDF-testis determining factor-> medullary tissue forms testis with seminiferous tubules and Leydig cells.
Female ext genitalia form regardless of ovary present

21
Q

Y Chromosome

A

TDF/SRY-sex determining region on Y
SRY strongly implicated in male sex determination, near pseudoautosomal boundary.
AZF-Azoospermia factors->AZF a,b,c. Deletion can lead to azoospermia->idiopathic infertility

22
Q

X chromosome inactivation

A

Barr body-> inactive X chromosome, extra X’s also inactivated to form barr bodies.
*Both male and female have ONLY ONE active X chromosome.

23
Q

X chromosome inactivation center

A

Xq13 and encodes for XIST gene-inactive X specific transcripts

24
Q

XIST

A

produces key regulatory non coding RNA that is only expressed on the inactive chromosome and transcriptionally silent on the active X
XIST RNA/Barr body complex

25
Q

Non random X chromosome inactivation

A

Normally see random inactivation.

unbalanced structure causes abn chrome to be inactive. Most X autosome translocations are non randomly inactivated

26
Q

X-linked mental retardation

A

high freq of mutations/microdeletions that cause X-linked mental retardation. common

27
Q

Monosomy X (Turner Syndrome)

A

less freq in live born, common in spontaneous abortions. Rare structural abns: isochrone of q of X chrome. Mosaicism is more common for sex chromes than autosomes

28
Q

Klinefelter Syndrome

A

50% errors in paternal meiosis.
Barr bodies
15% mosaic karyotypes

29
Q

Klinefelter Syndrome phenotype

A

Tall, thin males, long legs, hypogonadism appear at puberty, underdeveloped secondary sex characteristics, infertile, some psych probs

30
Q

47, XYY Syndrome

A

tall, attention deficit, hyperactivity, impulsiveness, normal intelligence, fertile, no increase in aggression or psychopathology.
Paternal meiotic nondisjuntion
Not assoc with clinical phenotypes

31
Q

Trisomy X (47, XXX)

A

above avg stature, no abn phenotype, fertile but increased risk of abn offspring, abn behavior, IQ below normal,
(48, XXXX)-restricted physical and mental dev
(49,XXXXX)-severe developmental retardation with multiple physical defects

32
Q

Turner Syndrome (45, X and variants)

A

50% 45,X

25% mosaic karyotypes, isochromosome X

33
Q

Turner Syndrome Phenotype

A

Short stature, webbed neck, Broad chest w/widely spaced nipples, coarctation of aorta, cystic hygroma, Low post. hairline, gonadal dysgenesis, renal and cardio anomalies, infantile edema of dorsum of foot
Above to avg. intelligence, worse social cognition skills if X from mother

34
Q

Hermaphroditism

A

presence of both ovarian and testicular tissue.

35
Q

Gonadal Maldevelopment: Camptomelic dysplasia

A

mutation in SOX9 gene which is involved in testes formation

36
Q

Gonadal Maldevelopment: Sex Reversed 46,XY

A 
subclass SRY not deleted-> testis formation at a critical point.
Duplication of Xp21->excess of DAX1 suppresses SRY and leads to ovarian development
37
Q

Denys-Drash Syndrome

A

female or ambiguous external genitalia, mutation in WT1 gene disrupts normal testicular development.
9p deletion syndrome->DMRT1 gene deletion which is involved with gonad development

38
Q

Female Pseudohermaphroditism

A

gonadal tissue of only one sex. 46, XX with ambiguous external genitalia usually caused by congenital adrenal hyperplasia.
-AR disorder arising from defects in enzymes for cortisol biosynth.
Ovarian dev normal, excess androgens cause masculinization-clitoral enlargement and labial fusion.
21-hydroxylase deficiency**

39
Q

Congenital Adrenal Hyperplasia

A

AR, cortisol and aldosterone deficiency, androgen overproduction- can affect both sexes.

40
Q

Congenital Adrenal Hyperplasia: Female phenotype

A

Female phenotype:enlarged clot with urethral opening at base-ambiguous.
Normal internal structures of repro tract
W/age->deep voice, appearance of facial hair, failure to menstruate at puberty.

41
Q

Congenital Adrenal Hyperplasia: Male phenotype

A

testes small at puberty, may cause adrenal crises in neonates due to salt wasting.
vomitting, dehydration, changes in electrolyte profile, cardiac arrythmia. death if untreated

42
Q

Male Pseudohermaphroditism

A

Deficiency of 5-reductase steroid!
Androgen insensitivity syndrome (AIS), lack of androgen receptors in target cells.
Normal female external genitalia, blind vagina, no uterus/uterine tubes.
AIS-X-linked inheritance

Genetics (12 decks)

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