Flashcards in Recurrent Miscarriage Deck (26):
What percentage of recognised pregnancies miscarry?
What percentages of miscarriages are chromosomal abnormal?
What are the most common autosomal trisomies reported in abortions?
16, 21, 22
What percentage of patau, Edward and DS miscarry?
95% for ed and pau and 80% for DS
Recurrence rate for a couple after pregnancy with autosomal trisomy? What possible reason is there if there is recurrance?
1%. Recurrance due to gonadal mosaicism
What percentage of couples with recurrent miscarriages have a balanced translocation?
What chromosomes can undergo a robertsonian translocation?
Acrocentric - 13, 14,15,21,22
What does Guichaoua et al 1990 say about robertsonian translocations and infertility?
Failure of trivalent pairing in58% of cells
12% of cells showed associations of unpaired 14 and 22 short arms with XY sex vesicles - disrupting meiosis and sperm failure
How do you describe an inversion?
Needs two breakpoints eg. 46,XX, inv(1)(p2q3)
True or false a pericentric inversion does NOT involve the centromere?
Possible Results of a pericentric inversion at during meiosis?
1)A normal chromosome
2)An inverted chromosome
3)Recombinant chromosome dup p distal(beyond breakpoint ) and q arm missing
4)recombinant chromosome dup q distal and p arm missing
3&4 make up 50%of cells
What are the possible results of the inversion loop in a paracentric inversion?
2) inverted chromosome
3) dicentric recombinant chromosome (tend to be lost in mitosis)
4) acentric recombinant chromosome (lost v.quick in other mitotic divisions )
Which has a higher risk of having an abnormal child - para or peri centric inversions?
Para has less risk of abnormal children as miscarriages occur earlier on but may have an increased risk of infertility
What is a balanced insertion?
V.rare with high risk of abnormal child
-3 breakpoints - part of one chromosome has inserted into another.
Eg. 7, der7, 12, der12 (q arm of 12 inserted into p arm of 7)
Result is balanced, normal, dup for insertion of del for insertion
Risk to carriers or balanced insertions?
Generally clinically normal but may have de novo translocation with the breakpoints disrupting a gene
Often have reproductive problems
What do normal chromosome pairs form at meiosis?
A bivalent - paired along whole chromosome
What do reciprocal translocations form at meiosis?
Quadrivalent- four different chromosomes pair a long common sequences
How do you draw segregation analysis?
Quadrivalent - line up with centromeres on the horizontal axis and chromosomes bend at the breakpoints
What are the segregation results of a quadrivalen?
The four chromosomes will segregate to daughter cells to form gametes
Either 2:2, 3:1, 4:0 (usually inviable)
What is alternate segregation and what is the outcome?
2:2 segregation (opposites in the quadrivalent) either the balanced products o the normal chromosomes
What is adjacent 1 segregation and what are the outcomes
2:2 Non homologous centromeres segregate together (from top or bottom of quad)
Adjacent 1 always results in imbalance
Adjacent 2 segregation?
2:2 homologous centromeres segregate together (either the left or right two)
Interchange tertiary trisomy /monosomy?
3:1 derivative chromosomes segregate to separate gametes
3:1, always imbalanced: derivative chromosomes segregate together
How to draw quad to find out the most likely segregation to have a viable child?
Draw two lines down the longest arms and this will show the most likely