Triploidy Flashcards
What is triploidy?
- Chromosomal anomaly seen in 1 - 2% of all conceptions and ~10% of spontaneous abortions
- 69,XXX or 69,XXY
- Most triploid conceptions end in the first trimester as spontaneous abortions, some reports of live births, with the longest reported survival of 10.5 months
Digyny
- Extra set of chromosomes = maternal
- Associated with asymmetric severe fetal growth restriction (FGR), pronounced wasting of body and sparing of head, normal NT-thickness and very low serum free beta-hCG & PAPP-A, and a very small placenta
- Usually occurs as a result of errors in meiosis I or meiosis II during oogenesis
Diandry
- Extra set of chromosomes = paternal
- Placenta = enlarged & partially molar
- Fetus = symmetric mild growth restriction or well grown fetus
- Fetal NT = high
- Maternal serum free beta-hCG = 10X higher than normal
- Diandric triploidy can also cause sever maternal complications, including severe early-onset preeclampsia and choriocarcinoma
Molar pregnancy
- When a non-viable fertilized egg implants in the uterus
- Can be complete or partial
- Tissue that normally would become a fetus instead becomes an abnormal growth in the uterus
- This growth triggers symptoms of pregnancy (occasionally RARE pregnancy that is though to be twins, one is molar and one is a real fetus)
Complete mole
- When either a single sperm or two sperm combine with an “empty” egg (without either a maternal nucleus or without maternal DNA)
- The sperm then reduplicates and forms a 46 chromosome set
- The tissue grows and looks similar to a cluster of grapes. It does not have fetal tissue.
Partial mole
2/3 of time: Two sperm fertilize an egg (dispermy) yielding paternal triploidy genotype –> results in abundant trophoblast and poor embryonic development
1/3 of time: Sperm fertilizes a diploid egg, yielding maternal triploidy genotype –> results in retardation of embryonic development and a small fibrocytic placenta
Risk factors for molar pregnancy
- Age >35
- Hx of molar pregnancy; especially 2 or more
- Hx of miscarriage
- Diet low in carotene (form of vitamin A) (women low in vitamin A have an increased rate of complete molar pregnancy)
- Certain ethnic groups (Filipinos)
Invasive Mole
- A hydatidiform mole that grew into the muscle layer of the uterus, can develop from complete or partial moles (more often complete)
- May spread to other parts of the body such as the vagina vulva and lung
Choriocarcinoma
malignant gestational trophoblastic cancer, usually of the placenta
Possible forms of inherited triploidy
There have been some reports of autosomal recessive triploidy and a susceptibility locus has been assigned to chromosome 19.
What method of NIPT would possibly pick up a case of triploidy?
DIANDRIC ORIGIN ONLY: Only the lab Natera, which uses targeted amplification and analysis of SNPs on chromosomes 21, 18, 13, X and Y in one reaction and determines the chromosomal copy number (cannot distinguish between twins and triploidy by this test alone)
Every other lab uses a counting method where the amounts of chromosomes 21, 18,13, X and Y are compared against other chromosome amounts as a reference and thus would not pick up triploidy.
Low fetal fraction on NIPT (through Natera), multiple congenital anomalies, and fetal growth restriction would be indicative of _________________
Digynic triploidy.
This is most likely due to the associated small placental mass.
If you have 2 maternal copies of a genome only, what kind of tissue would develop?
Fetal tissue only, “benign cystic teratoma”
With 2 paternal copies of a genome only, what kind of tissue would develop?
Placental tissue, no fetal tissue
Hydatidiform mole
Clump of growing tissue
