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Flashcards in Mosaicism Deck (26):
1

What is somatic mosaicism

Mosaicism that only occurs in the body (soma) so can't be passed on
earlier in embryogenesis it occurs the higher the fraction cells affected

2

What's segmental mosaicism

Where some body parts have abnormality and display the phenotype and some ares don't

3

What's is germline mosaicism

Usually not detected until the person has had to affected children by and apparently de novo abnormality
Only occurs in the gonads
Arises during the formation of the gonads (~30mitotic divisions prior to meiosis where this could occur)

4

What's somatic gonadal mosaicism

Both soma and germline cells involved

5

What's dynamic mosaicism

Description of mosaicism for rings
At cell division rings are broken/ doubled/ entangled results in different ring structure in diff cells

6

What 2 types of mosaicism are seen in fragile X syndrome

Mutational (diff sized expansions due to somatic instability of the repeat) ~ 20% males
Methylation (same sized expansion in all cells but with varying methylation patterns)

7

What is confined placental mosaicism

An abnormal cell line is present only in the placenta and not the foetus. Usually because of an event later on once fetal and extraembryonic lineages had diverged.
Present in CVS, not in AF

8

What are the two ways mosaicism can occur

Postzygotic Mitotic NDJ (majority of cases)
Trisomy rescue

9

Describe postzygotic Mitotic NDJ

Non disjunction occurs postzygotically resulting in a normal, trisomic and monosomy cell line.
The monosomy cell line will die out due to growth deficiency leaving the normal and the trisomic cell line

10

Describe trisomy rescue

Anaphase lag of a trisomic conceptus
Loss by delayed movement of the additional chromosome
Either by failure to attach to the spindle or by moving slowly-
Results in it not being incorporated into the Newley forming daughter cell, forming a micronucleus and being lost

11

Which mosaicism are associated with trisomy rescue

mT13
mT21
mT18
45,XO

12

Which mosaicism is associated with postzygotic NDJ

mT8

13

What is hypomelanosis of Ito

Heterogeneous group of disorders characterised by HYPOpigmentated skin and streaks that follow the Blaskhos lines with neurological defect, epilepsy, asymmetrical abns of organs

14

What disorders are associated with Hypomelanosis of Ito

Polyploidy
Anueploidy
Del/ ins/t

15

What's a correcting event

Mosaicism in lymphocytes of affected patients whereby spontaneous reversion to the wt state is observed
Resulting a a false positive result
Only occurs in lymphocytes (lymphoid precursor)

16

What disorders are associated with correcting events

Fanconi anaemia: 25% pts
Bloom's syndrome: 20%pts

17

What is age related mosaicism

Women lose an X with age
Men loose Y with age

18

What is considered significant loss of X in a blood sample

99th centime on a 30 cell count:
30yrs: 6%
40yrs: 9%
50yrs: 13%
60yrs: 17%

19

What disease are associated with loss of Y in bone marrow

MDS, MPD, AML, LPD

20

Name some tissue specific mosaicism disorders

Pallister Killian: +i(12p) seen in fibroblasts (cultured out of blood)
mT20: abn cells in renal and genitourinary tract/ buccal epithelial cells/ fibroblasts
mT8: better tolerated in fibroblasts

21

Name some monogenic disorders associated with mosaicism

Neurofibromatosis 1: somatic gonadal mosaicism for germline mutation/ occasional segmental mosaicism
mcCune-Albright syndrome: GNAS: SOMATIC MOSAICISM not inherited
Osteogenesis Imperfecta type 2: COL1A1/ COL1A2: GERMLINE MOSAIC PARENT

22

Name the 3 types of mosaicism

Somatic
Germline
Somatic gonadal

23

What counts are required to exclude mosaicism at 10%

90% confidence: 22 cells
95% confidence: 29 cells
99% confidence: 44 cells

24

What counts are required to exclude mosaicism at 5%

90% confidence: 45 cells
95% confidence: 59 cells
99% confidence: 90 cells

25

Describe briefly mitochondrial mosaicism

at cell division the mitochondria segregate randomly
They also have a high mutation rate
So mosaicism is both # in cells and mutations within those mitochondria

26

What's considered normal loss of the X chromosome in cultured blood samples for females.

Thirty years it's less than 1 %. Forty years it's 2%, at fifty years it's 3%, at sixty five years it's 5%