3. Triploidy and molar pregnancies

Question 1

What is diandry?

Answer 1

Double paternal contribution, most common type of triploidy

Question 2

What are the causes of diandry?

Answer 2

1. Fertilisation of normal ovum by 2 sperm (dispermy)
2. Diploid sperm (non-disjunction of entire set of chr. in spermatogenesis)
3. Normal fertilisation followed by duplication of all chr.

Question 3

What is digyny?

Answer 3

Triploidy; double maternal contribution

Question 4

What are the causes of digyny?

Answer 4

1. Fertilisation of diploid ovum (non-disjunction at MI or MII)
2. Diploid ovum due to retention of polar body in a fertilised egg
3. Fertilisation of unovulated primary oocyte (2n)
4. Fusion of 2 eggs

Question 5

What is the diandric phenotype?

Answer 5

Large, cystic placenta

Symmetrical IUGR

Neural tube defects

Oligohydramnios

Normal adrenal glands

High maternal hGC

Generally abort at ~12 weeks

Question 6

What are the histological features of a partial mole?

Answer 6

Two populations of villi- small normal and and enlarged, hydropic

Irregular villi with scalloped edges

Question 7

What is the digynic phenotype?

Answer 7

Asymmetrical IUGR

Small placenta

Adrenal hypoplasia

Holoprosencephaly

Oligohydramnios

Usually abort at ~10 weeks

Question 8

What is a hydatidiform mole?

Answer 8

Most common form of gestational trophoblastic disease - arise from villous trophoblast that normally forms placenta

Question 9

What is a complete molar pregnancy?

Answer 9

Diploid pregnancy, both sets of chr. are paternally derived

75% of hydatidiform moles

No formation of fetus, leads to trophoblastic hyperplasia

Question 10

What are the possible causes of complete molar pregnancies?

Answer 10

Fertilisation of anucleated egg by normal haploid sperm - chr. then duplicated

Dispermic fertilisation of anucleated egg

Question 11

What is a partial molar pregnancy?

Answer 11

Triploid pregnancy caused by diandry

Abnormal fetus/embryo

Question 12

What is the effect of molar/partial molar preganancies?

Answer 12

Overproduction of trophoblastic tissue which go on to form placenta

Excess trophoblast tissue grows into abnormal masses

Question 13

What is the recurrence risk for complete and partial molar pregnancies?

Answer 13

Complete: 1/100 after one, 1/5 after two

Partial: 1/600

Recurrence can be same or different type

Question 14

What are the 2 categories of gestational trophoblastic disease?

Answer 14

1. Pre-malignant - complete and partial hydatiform moles
2. Malignant - Gestational trophoblastic neoplasia

Question 15

What are the 3 forms of gestational trophoblastic neoplasia?

Answer 15

1. Invasive mole - usually arises from complete mole
2. Choriocarcinoma - malignant, aggressive tumour of uterine wall. Usually occur when growths from molar pregnancies turn cancerous
3. Placental site trophoblastic tumour - commonly follows normal pregnancy

Question 16

What is FRHM?

Answer 16

Familial recurrent hydatiform moles

AR, predispostition to molar pregnancies - usually complete moles, diploid, biparental origin

Moles are indistinguishable from sporadic moles

Question 17

What genes are mutated in FRHM? What is their role?

Answer 17

NLRP7 and KHDC3L genes - role in maintaining maternal imprint in ovum

Question 18

What is the result of maternal UPD for the full chromosome complement?

Answer 18

Benign cystic ovarian teratoma