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M2M Week3 > Imprinting, Cytogenetics, DS, PWS > Flashcards

Imprinting, Cytogenetics, DS, PWS Flashcards

1
Q

epigenetics

A

Mitotically and meiotically heritable variations in gene expression that are not caused by changes in DNA sequence. Ex. DNA methylation and post-translational modifications of histones

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2
Q

Compact vs. open chromatin

A

Compact is repressed through methylation and repressive histone marks. Open has active histone marks and is not methylated

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3
Q

Methylation of CpG islands recruits which protein to silence gene expression?

A

MeCP2 recognized methylated cytosine. Recruits other proteins involved in repression

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4
Q

Genetic imprinting

A

Sex-dependent epigenetic modulation of regulatory regions. Males and females have different regions that are turned on or off via methylation of CpG islands. Less than 10% of genes

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5
Q

When is methylation established? Is it maintained or reversible?

A

Established in the gamete. Maintained in somatic cells but has to be reversible so it can be reset during gametogenesis.

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6
Q

Which enzyme propogates epigenetic marks in somatic cells?

A

Methytransferases. Methylate newly synthesized DNA strand

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7
Q

What are the DNA methylation imprinting patterns in germ line and somatic cells?

A

Epigenetic reprogramming occurs in germ cells. Somatic maintenance of imprinted regions occurs in somatic cells.

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8
Q

Why is erasure/resetting of methylation patterns of imprinted genes essential during gametogenesis?

A

Without erasure/resetting; half of primordial germ cells will have wrong imprinting. Ie; 1/2 of PGCs from each parent will have male imprinting and female imprinting.

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9
Q

What is deleted in Prader-Willi Syndrome?

A

Del(15q11-q13) on paternal chromosome. Only have maternal piece

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10
Q

What is deleted in Angelman syndrome?

A

Del(15q11-q13) on maternal chromosome. Only have paternal piece

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11
Q

What is the role of the imprinting center?

A

It �decides� which regions are expressed from maternal/paternal chromosome

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12
Q

What 3 mechanisms can cause PWS?

A

1) Deletion of paternal 15q11-13 (most common) 2) Maternal uniparental disomy (both chromosomes in this region came from mom) 3) Imprinting center is missing/mutated on paternal allele

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13
Q

What 4 mechanisms cause AS?

A

1) Deletion of maternal 15q11-13 (most common) 2) Paternal uniparental disomy 3) IC mutated/missing on maternal allele 4) Mutation of UBE3A gene on maternal allele (this is the only maternal gene that gets expressed in this region)

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14
Q

What leads to deletions in PWS/AS?

A

Presence of low copy repeats derived from gene HERC2. The repeats flanking 15q11-q13 may be involved in misalignment with leads to deletions during homolougs recombination.

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15
Q

What translocation is seen in chronic myeloid leukemia (CML)?

A

t(9;22)

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16
Q

What protein fusion product is commonly seen in CML?

A

BCR/ABL fusions

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17
Q

How can CML be treated?

A

Tyrosine kinase inhibitors aka Gleevec

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18
Q

How does Gleevec work?

A

In cells; phosphorylation is an “on” switch. In Ph-+ CML cells BCR-Abl is stuck in “on” and keeps phosphorylating groups. Gleevec binds to Abl or BCR-Abl and prevents phosphorylation. In turn prohibits cell proliferation.

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19
Q

What translocation is seen in acute pro-myeloid leukemia (APMO)?

A

t(15;17)

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20
Q

What protein fusion product is commonly seen in APMO?

A

PML-RARalpha

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21
Q

How can APMO be treated?

A

Retinoic acid aka Vitamin A (I think it has to be all-trans).

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22
Q

How does retinoic acid work?

A

It changes the conformation of the novel protein so that it allows for differentiation again.

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23
Q

What the common cytogenetic findings in childhood B-cell acute lymphoblastic leukemia (ALL)? How do cytogenetic findings influence patient prognosis?

A

High hyper-diploidy. High hyper-diploidy is good prognosis.

24
Q

Name 5 types of FISH probes

A

Centromere; locus specific; dual fusion/fusion; break apart; whole chromosome paint

25
Q

What is the name of the centromere FISH probe? What is it used for? What is an example?

A

Cen. Used for enumeration. Ex ALL panel; prenatal dx

26
Q

What is the name of the locus specific FISH probe? What is it used for? What is an example?

A

LIS. Used for deletion/duplication. Ex p53 cancer

27
Q

t is the name of the dual fusion/fusion FISH probe? What is it used for? What is an example?

A

DF;F. Used for translocation. Ex BCR-Abl; PML-RARalpha cancers

28
Q

t is the name of the Break Apart FISH probe? What is it used for? What is an example?

A

BAP. Used for translocation rearragment. Ex MLL (cancer)

29
Q

t is the name of the Whole Chromosome Paint FISH probe? What is it used for? What is an example?

A

WCP. Used for indentifying markers; translocations. Ex WCP 1-22; X; Y (all studies)

30
Q

What are the 3 main causes of Down Syndrome?

A

Trisomy 21; Unbalanced translocation btwn 21 and another acrocentric chromosome (3-4%); Mosaic Tri 21 (1-2%)

31
Q

What does 1st trimester screening for DS look at?

A

Ultrasound measurement of nuchal folds + Beta-hCG (human chorionic gonadotropin) + PAPP-A (pregnancy-associated plasma protein A). Detetion rate 82-87%

32
Q

What does 2nd trimester screening for DS look at?

A

Quad screen. Beta-hCG (human chorionic gonadotropin); AFP (alpha-fetoprotein); unconjugated estriol; and inhibin level

33
Q

If there is suspicion of DS based on 1st or second trimester screening; how can it be confirmed?

A

Chromosome analysis via amniocentesis or CVS (chorionic villus sampling)

34
Q

What are common physical features of infants with DS?

A

Growth parameters are usually normal; midfacial hypoplasia; upslanting palpebral fissures; epicanthal folds; small ears; large-appearing tongue; low muscle tone; increased joint mobility; short fingers; transverse palmar crease; Vth finger incurving (clinodactyly); increased space between toes 1 and 2

35
Q

What are common gastrointestinal structural anomalies seen in DS?

A

Esophageal atresia; duodenal atresia; hirschsprung’s. (Present in 10-15% of infants)

36
Q

What functional GI issues do many children with DS have?

A

Feeding problems; constipation; GERD - all very common. Celiac Dz (recommended screen is TTG + IgA)

37
Q

What % of DS Pts have cardiac issues? What is most common?

A

50%. All types of anomalies may be present butAtrioventricular Canal is common to DS

38
Q

What type of ophthalmologic problems are common in DS?

A

Blocked tear ducts; myopia; lazy eye; Nystagmus; Cataracts

39
Q

What ENT problems are common in DS pts?

A

Chronic ear infections; Deafness (sensorineural and conductive); chronic nasal congestion; enlarged tonsils and adenoids (obstructive apnea)

40
Q

What Orthopedic problems are common in DS?

A

Hips; joint subluxation; atlantoaxial subluxation

41
Q

What endococrine problems are common in DS?

A

Thyroid dz (most commonly hypothyroidism); Insulin Dependent Diabetes; Alopecia Areata; reduced fertility (but normal puberty)

42
Q

What hematologic issues are common in DS?

A

Myeloproliferative disorder in the newborn; increased risk of leukemia (12-20x); Iron deficiency anemia

43
Q

What developmental issues are common in DS?

A

Hypotonia delays gross motor development; Spectrum of intellectual disability (mild-moderate disabilities); speech problems (importance of sign language)

44
Q

What psychiatric issues are seen in DS?

A

Depression; early Alzheimer�s; Autism (1/10)

45
Q

What neurologic problems are common in DS?

A

Hypotonia (spectrum from mild-severe); Seizures (especially infantile spasms)

46
Q

How do Prader-Willi newborns present?

A

Present with hypotonia; dysmorphic features (almond shaped eyes); undescended testicles; severe feeding problems; lighter pigmentation

47
Q

What type of ophthalmologic problems are common in Prader-Willi?

A

Many; especially strabismus and nystagmus

48
Q

What kind of testing can be done for PWS?

A

Can test for methylation of 15q11-13 OR if there is a deletion you would test with FISH or microarray

49
Q

How do PWS toddlers/preschoolers present?

A

Feeding problems completely reverse. Can lead to obesity

50
Q

What kind of orthopedic problems are common in PWS?

A

scoliosis

51
Q

What kind of respiratory problems are common with PWS?

A

Obstructive sleep apnea may develop and is a contraindication to use of growth hormone**

52
Q

What kind of developmental problems are common in PWS?

A

Mild-moderate cognitive disabilities; behavioral issues

53
Q

What other disorders are associated with chromosome 15Q?

A

Marker Chromosomes -Inverted duplication; Interstitial duplications; Deletions (Angelman syndrome). Also linkage disequilibrium btwn Autism and GABA-alpha-b3 locus on 15q

54
Q

What is the phenotype of Pts with IDIC 15 AND maternally derived interstitial 15q duplications?

A

Autism; NOT dysmorphic; seizures common; hypotonia common during infancy

55
Q

What is the phenotype of Pts with Angelman Syndrome?

A

dysmorphic facial features; hypotonia in infancy progressing to spasticity; Intellectual Disability (ID); seizures; autism

M2M Week3 (5 decks)

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