(dev&age) disorders of early development Flashcards
what are three causes of pregnancy loss?
errors in embryo-fetal development
failure of the embryo to interact with the maternal endometrium and implant in the uterine lining
inability to sustain development of an implanted embryo/fetus
define miscarriage
loss of a pregnancy prior to 23 weeks gestation
what are the two classifications of miscarriage?
early clinical pregnancy loss (<12 weeks gestation)
late clinical pregnancy loss (>24 weeks gestation)
why is miscarriage classified based on a 23-24 week window?
as after 24 weeks there is a baseline levels of foetal viability outside the womb
(in case the fetus needs to be delivered)
what is early clinical pregnancy loss?
pregnancy loss before 12 weeks (i.e. in the first trimester)
what is late clinical pregnancy loss?
pregnancy loss after 24 weeks (i.e. in the second/third trimester)
how can a pregnancy be detected?
either by detected hCG in the mother’s urine OR by detecting the fetal heartbeat on an ultrasound scan
what is recurrent miscarriage?
recurrent pregnancy loss
in the UK = three or more pregnancy loss (either consecutive or non-consecutive)
what is recurrent miscarriage alternatively known as?
recurrent pregnancy loss
how many miscarriages must a woman have to be diagnosed with RM/RPL?
three or more consecutively OR non-consecutively
what are the two classifications of pregnancy loss?
pre-clinical pregnancy loss
clinical pregnancy loss
what is pre-clinical pregnancy loss?
the loss of a conceptus prior to implantation (pre-implantation) OR following implantation but before the missed menstrual period, approx 3-4 weeks gestation (post-implantation)
what is clinical pregnancy loss?
the loss of a conceptus following implantation but after the missed menstrual period (3-4 weeks gestation)
differentiate between pre-clnical and clinical pregnancy loss
pre-clinical pregnancy loss is either pre-implantation or post-implantation but before the missed menstrual period (i.e. 3-4 weeks gestation)
whereas clinical pregnancy loss is post-implantation after the missed menstrual period (i.e. after 3-4 weeks gestation)
how common is pre-clinical pregnancy loss?
pre-implantation = approx 30%
post-implantation (up to 3-4 weeks gestation) = another 30% approx
how common is clinical pregnancy loss?
approx 10%
how does the risk of clinical pregnancy loss change with maternal age?
as maternal age increases, the risk of clinical pregnancy loss also increases
what proportion of conceptions actually end up in successful live births?
approx 30%
what is the main cause of early pregnancy loss?
aneuploidy (chromosomal number errors)
what is aneuploidy?
having missing or extra chromosomes
what percentage of embryos are likely to be aneuploid?
approx 50%
what is the relationship between trisomic pregnancy risk and maternal age?
as maternal age increases, the risk of trisomic pregnancies increases exponentially
what is a trisomic pregnancy?
wherein the fetus has an extra chromosome in either some or all of the body cells
explain how oocytes undergo meiosis in the developing foetus
- eggs in ovary enter meiosis
- maternal and paternal copy pair up and DNA is replicated so there are two chromatid per chromosome
- homologous chromosomes lin up
- exchange material in recombination
- become arrested (do not proceed through to the first meiotic division)
- paternal and maternal chromosomes remain arrested in this linked state (i.e. dictyate state) all through life until the point at which the specific oocyte is about to get ovulated
- once ovulated THEN first meiotic division resumes
how is genetic material exchanged between homologous chromosomes?
homologous chromosomes line up and crossing over takes place between the chromatids of the chromosomes = genetic recombination
when do the foetal chromosomes in the developing ovary become arrested?
become arrested just after genetic recombination takes place and just before the first meiotic division can occur
what is dictyate arrest?
the prolonged resting phase in oogenesis wherein the oocytes become arrested in prophase I just before the first meiotic division until ovulation
for how long do the oocytes remain in dictyate arrest?
up to 50 years between the creation of an egg in foetal life TO point of oocyte ovulation = until then oocytes remain in dictyate arrest
describe the structure of the replicated chromosome in the ovary of the developing foetus
chromosomes, once replicated, are made up of two chromatids, joined together by cohesin proteins
how are chromatids held together?
cohesin proteins
what are cohesion proteins?
proteins that hold together sister chromatids of homologous chromosomes and provide cohesion
when does meiosis commence in oocytes?
during foetal life
post DNA replication, how many chromatids are there per chromosome?
two chromatids per chromosome
how long does dictyate arrest last?
the oocytes become arrested in prophase I just before the first meiotic division until ovulation
i.e. depending on when ovulation takes place, dictate arrest can last up to 50 years
compare the cohesion proteins in a young oocyte to that of an older oocyte
in young oocytes = many cohesion proteins link the chromatids of homologous chromosomes together
in older oocytes = cohesion proteins are lost and not replaced so the cohesion between chromatids is also lost
how do the first and second meiotic divisions occur in oocytes post ovulation?
when the oocyte is ovulated, the first meiotic division occurs as the spindle fibres separate the homologous chromosomes
the second meiotic division occurs when the spindle fibres separate the chromatids of a homologous chromosome
what separates in the first meiotic division?
the paired homologous chromosomes
what separates in the second meiotic division?
the (joined) chromatids of a homologous chromosome
what happens to the cohesion proteins as the oocyte gets older?
cohesion proteins are gradually lost and not remade or replaced so cohesion between the chromatids is also lost with increasing age of the oocyte
how are lost cohesion proteins replaced?
the lost cohesion proteins are not remade or replaced
what happens to cohesion proteins with increasing maternal age?
as the oocyte gets older, cohesion proteins are gradually lost and not replaced so there is a loss of cohesion between the chromatids
how does the loss of cohesion proteins impact meiosis?
as there is a loss of cohesion between the chromatids of the homologous chromosome, the chromatids can separate and drift randomly during meiotic division
= are not segregated accurately + do not line up properly
= can lead to aneuploidy
what is the impact of cohesion proteins not being replaced?
cohesion between the chromatids is lost
why does increasing maternal age lead to increased risk of aneuploidy?
increased maternal age = older oocytes = greater loss of cohesion proteins between the chromatids
greater loss of cohesion between chromatids so during spindle fibre anaphase in meiosis, less likely to be segregated accurately and will drift randomly
= can lead to aneuploidy
how does the lack of cohesion proteins with age lead to aneuploidy?
greater loss of cohesion between chromatids so during spindle fibre anaphase in meiosis, less likely to be segregated accurately and will drift randomly
= can lead to aneuploidy
what essential structure do cohesion proteins form and why is this important?
cohesion proteins form a ring structure that holds the two chromatids of a chromosome together
= if it is lost, chromatids cannot be held together properly and will drift apart
why is an increased maternal age risky for pregnancies?
increased maternal age = older oocytes = greater loss of cohesion proteins between the chromatids
greater loss of cohesion between chromatids so during spindle fibre anaphase in meiosis, less likely to be segregated accurately and will drift randomly
= increased risk of aneuploidy
what signalling pathway underpins recurrent pregnancy loss?
Lif pathway
what has been seen in Lif-deficient mouse models that can tell us about RPL/RM in humans?
while there is normal embryo development, there is failed implantation in Lif-deficient mouse models
define subfertile
women that can conceive normally but take longer than normal
(i.e. delay in conceiving)
describe the endocrine signalling impairment in subfertile women
reduced levels of Lif in the uterine secretions of subfertile women
what is the non-selective uterine hypothesis?
the idea that some uteruses have a high permissibility for implantation and they lose selectivity to poor quality embryos due to genetic and compositional changes in the mucin proteins
= so poor quality embryos are (abnormally) allowed to interact with the maternal endometrium and implant but cannot develop = RPL/RM
why do some uteruses lose their selectivity to poor-quality embryos?
there are genetic and compositional changes in the mucus and mucin proteins = cause the changes in permissibility of the maternal uterus to implantation
what happens when poor-quality embryos are allowed to implant into the maternal endometrium?
can implant but cannot develop properly
= can underpin pathophysiology of RPL/RM
which changes account for the increased permissibility of the maternal uterus to implantation?
genetic and compositional changes in the maternal mucus and mucin proteins
what do embryos require to be viable?
a balance between (1) both maternally and paternally-derived genomes (2)
how can normal embryonic development be ensured?
by ensuring both the maternal and paternal genome is present AND there is a balance between both genomes
why are both maternally and paternally derived genomes essential for embryonic viability?
their presence and a balance between the two genomes ensures normal embryonic development (= results in embryonic viability)
what would be seen if the embryo had only maternally-derived DNA?
huge fetus, very tiny placenta
what would be seen if the embryo had only paternally-derived DNA?
very tiny fetus, huge placenta
why is there a conflict between maternally inherited and paternally inherited genes?
some genes are only expressed in the maternally inherited copy whereas others are only expressed in the paternally-inherited copy
what do paternally inherited copies of genes promote?
promote embryo fitness and development at the expense of the mother
(i.e. encourage fetus to take as much resource out of the mother for embryonic development)
what do maternally inherited copies of genes promote?
restrict embryo fitness to conserve resources for future pregnancies
(i.e. allow embryonic development but not at the expense of the maternal resources that are saved for future pregnancies as well)
compare the difference in effects of maternally and paternally inherited genes
paternal = encourage embryonic development at the expense of the maternal resources
maternal = encourage embryonic development but NOT at the expense of the maternal resources, of which some are conserved for future pregnancies
(= intergenomic conflict)
explain the intergenomic conflict caused by maternally and paternally inherited genes
while paternally inherited genes encourage embryonic development at the expense of the mother’s resources, maternally inherited genes encourage embryonic development BUT also conserve the maternal resources for future pregnancies
which genes are most commonly involved in the intergenomic conflict between maternally and paternally inherited genes
genes involved in placentation and nutrition
what are GTDs?
gestational trophoblastic diseases
what are gestational trophoblastic diseases?
diseases wherein there is an abnormal overgrowth of trophoblastic tissue (i.e. cells that form the placenta) which develops into benign or malignant tumours
can occur during or after a pregnancy
what is there an overgrowth of in GTDs?
trophoblastic tissue (i.e. would otherwise develop into healthy placenta)
what are the two types of gestational trophoblastic disease?
benign = hydatidiform moles
OR
malignant = gestational trophoblastic neoplasias
what are benign GTDs?
complete OR partial hydatidiform moles
i.e. form from the abnormal overgrowth of trophoblastic tissue
what is the incidence of hydatidiform moles?
1/500 to 1/5000 pregnancies (depending on geography)
what are hydatidiform moles?
abnormal overgrowth of trophoblastic tissue within the uterus either during or after a pregnancy
what are the two types of hydatidiform moles?
complete OR partial
what are complete hydatidiform moles?
moles where there is overgrowth of trophoblastic tissue but foetal tissue is absent
what are partial hydatidiform moles?
moles where there is overgrowth of trophoblastic tissue but some foetal tissue is present
differentiate between complete and partial hydatidiform moles
while both moles result from abnormal overgrowths in trophoblastic tissue, complete hydatidiform moles have no foetal tissue present whereas partial hydatidiform moles have some foetal material present
what are malignant GTDs?
gestational trophoblastic neoplasias
how do malignant GTDs arise?
arise from the incomplete evacuation of hydatidiform moles from the uterus
(i.e. if some trophoblast tissue from a hydatitidorm mole is left behind and not fully extracted = can give rise to a malignant gestational trophoblastic neoplasia)
what are the rare types of malignant GTDs?
invasive mole
choriocarcinoma (fast-growing cancer of the uterus)
what are the extremely rare types of malignant GTDs?
placental site trophoblastic tumour (PSTT)
epitheloid trophoblastic tumour
what happens when hydatidiform moles are incompletely extracted?
the remaining portion of the hydatidiform mole can become cancerous and give rise to a gestational trophoblastic neoplasia
differentiate between benign and malignant GTDs
benign GTDs occur in the form of complete or partial hydatidiform moles and are less invasive
malignant GTDs occur in the form of gestational trophoblastic neoplasias from the remiander of partially extracted hydatidiform moles and are more invasive
what are the two ways in which complete hydatidiform moles can arise?
1) empty egg + one sperm that duplicates it genome = two paternal genomes
2) empty egg + two sperm (no duplication) = two paternal genomes
what are the two ways in which partial hydatidiform moles can arise?
1) normal haploid egg + one sperm that duplicates it genome = one maternal and two paternal genomes
2) normal haploid egg + two sperm (no duplication) = one maternal and two paternal genomes
differentiate between the ways in which complete and partial hydatididiform moles arise
complete hydatidiform moles arise from the fertilisation of an empty oocyte by either one or two sperm
partial hydatidiform moles however arise from the fertilisation of a normal haploid oocyte by either one or two sperm
how does the imbalance of the maternal and paternal genome result in hydatidiform moles?
imbalance of maternal and paternal genomes stimulates aberrant overgrowth of trophoblastic tissue = hydatidiform mole
(in complete hydatidiform moles = two paternal genomes)
(in partial hydatidiform moles = two paternal and one maternal genome)
what causes the aberrant development of trophoblastic tissue in hydatidiform moles?
the imbalance between maternal and paternal genomes
how does a hydatidiform mole/molar preganacy placenta look in comparison to a normal pregnancy placenta?
in molar pregnancy = large fluid-filled spaces that arise from the chorionic villi
what is an ectopic pregnancy?
a pregnancy wherein there is implantation of the embryo at a site other than the uterine endometrium
where do ectopic pregnancies occur?
fallopian tube, ovary, cervix and other intra-abdominal sites
where do ectopic pregnancies occur most commonly?
fallopian tube (approx 98% of ectopic pregnancies)
how common are ectopic pregnancies?
quite common
occur in 1/100 to 1/75 pregnancies
what is the treatment for ectopic pregnancies?
expectant management (resolve itself without intervention)
chemotherapy (methotrexate)
surgery (removal of the trophoblast OR fallopian tube itself)
how can ectopic pregnancies be treated with chemotherapy?
give methotrexate
how can ectopic pregnancies be treated with chemotherapy?
give methotrexate to destroy proliferative tissue
why are ectopic pregnancies very risky?
they can cause the fallopian tube to rupture which can lead to severe internal bleeding
how can ectopic pregnancies occur in the ovary?
once the oocyte is fertilised, instead of travelling down to the uterus, it can travel backwards and implant in the ovary
how can ectopic pregnancies occur in the cervix?
once the oocyteis fertilised, it travels down the uterus and towards the vagina, implanting in the cervical wall
which component of cigarette smoke affects the smooth muscle of the fallopian tube?
cotinine
what is cotinine?
a component of cigarette smoke
that regulates the expression of PROKR1 (regulator of fallopian tube smooth muscle contractility)
what is PROKR1?
a regulator of fallopian tube smooth muscle contractility
what regulates fallopian tube smooth muscle contractility?
PROKR1 (prokineticin receptor 1)
what are the main effects of cotinine?
1) disrupts PROKR1 = smooth muscle contractility is impaired
2) induce pro-apoptosis protein expression in fallopian tube = there in increased epithelial cell death
how does cotinine affect the fallopian tube smooth muscle?
disrupts PROKR1 so smooth muscle contractility is impaired
how does cotinine affect the fallopian tube epithelium?
induces pro-apoptosis protein expression in the fallopian tubes so there in increased epithelial cell death
how does tobacco smoke affect the fallopian tube?
inhibits ciliary function so reduced tubal transit for the embryo (i.e. the embryo cannot be moved along the tube) = gets stuck so can implant in the tubes
how is the tubal transit of the embryo reduced due to smoking?
tobacco smoke can impair ciliary function so there is reduced tubal transit of the embryo
how does smoking increase the risk of an ectopic pregnancy?
1) cotinine disrupts PROKR1 so smooth muscle contractility is impaired = FT cannot efficiently contract the push embryo down to uterus
2) cotinine stimulates pro-apoptosis protein expression = causes increased epithelial cell death
3) tobacco smoke causes impaired ciliary function so there is reduced tubal transit of the embryo
what are cannabinoid receptors?
receptors in the body that bind both endogenous cannabinoids (e.g. 2-AG, anandamide) and exogenous cannabinoids (i.e. cannabis)
which cannabinoid receptors does the fallopian tube epithelium express?
CB1 and CB2
how does the cannabinoid receptor expression differ in ectopic pregnancy patients?
in ectopic pregnancy patients, CB1 levels are reduced
bad because normal endocannabinoid signalling is needed to prevent ectopic pregnancies
what are CB1 knockout mice and what have they displayed?
mice with fallopian tubes that do not have CB1 receptors
= display embryo retention in the fallopian tubes
= suggests that endocannabinoid signalling is important for embryo transit down the fallopian tubes
what happens when there is a lack of CB1 receptors and what does this suggest?
fertility maintained BUT the embryo cannot transit properly down the fallopian tube = so increased risk of getting stuck = i.e. increased risk of ectopic pregnancy
why are CB1 and CB2 receptors important?
normal endocannabinoid signalling is necessary to ensure the smooth tubal transit of the embryo down the fallopian tubes
(i.e. to prevent ectopic pregnancies)
what are endocannabinoid levels like in ectopic pregnancy patients?
there are elevated endocannabinoid levels in ectopic pregnancy patients
how does cannabis use affect the fallopian tube?
components in cannabis such as THC may act directly on the fallopian tube to perturb embryo transit
endocannabinoid tone is altered in the tube leading to a disrupted embryo environment
how does cannabis use increase the risk of an ectopic pregnancy?
exogenous cannabinoids (i.e. adding more cannabinoids into the system) will act on CB1 and CB2 to disrupt and overwhelms the endocannabinoid signalling process
disrupts endocannabinoid tone as there is a disruption to the balance between the synthesis and breakdown of cannabinoids
= disrupts the normal function of the fallopian tubes and embryo transit
= increase risk of embryo retention and ectopic pregnancy
what is endocannabinoid tone?
the balance between the production and breakdown of endogenous cannabinoids
why is endocannabinoid tone important?
regulates how much endogenous cannabinoid is produced and how much is broken down
= influences the endocannabinoid signalling through CB1 and CB2 receptors
= influences transit of embryo along the fallopian tube
why is the loss of endocannabinoid tone harmful?
disrupts the endocannabinoid signalling through the CB1 and CB2 receptors
= so the transit of the embryo through the fallopian tube is impaired
= increased risk of embryo retention in the fallopian tubes and ectopic pregnancy
how do exogenous cannabinoids act on the fallopian tube?
can bind to CB1 and CB2 receptors which can overwhelm/disrupt the endocannabinoid signalling
= can impair embryo transit through fallopian tube
why are exogenous cannabinoids harmful?
(can bind to CB1 and CB2 receptors and disrupts the endocannabinoid signalling process in the fallopian tubes)
= increased embryo retention and increased risk of ectopic pregnancies
how does THC in cannabis affect the ectopic pregnancy risk and why?
can act directly on the fallopian tube to perturb embryo transit
what are endocannabinoid levels and CB1 levels like in ectopic pregnancy patients?
endocannabinoid levels are elevated
CB1 levels are reduced
