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Embryology > Teratology > Flashcards

Teratology Flashcards

1
Q

What is meant by “teratology” or “dysmorphology”?

A
  • it is defined as the study of congenital malformations (birth defects)
  • these are abnormalities that occur during development that lead to specific phenotypic presentations
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2
Q

What are the 4 different types of congenital malformations?

What do they all have in common?

A
  1. structural
  2. metabolic
  3. functional
  4. behavioural
  • they are all caused by a substance crossing the placenta
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3
Q

How common are major and minor congenital malformations?

A
  • major structural anomalies affect 3% of live-born infants
  • minor anomalies affect 15% of live-born infants
    • these may not directly affect the health of the child, but act as a clue to investigate underlying major abnormalities

congenital malformations account for 25% of infant deaths

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4
Q

What are the 3 categories of causes of congenital malformations?

A
  • they can be caused by environmental factors (15%)
  • they can be caused by genetic factors (30%)
  • or they can be caused by interaction of the environment with a person’s genetic susceptibility (55%)
  • most congenital malformations are multifactorial, and for most of these, the details of their origin are unknown
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5
Q

Why is it important to recognise minor abnormalities in children?

A
  • minor structural abnormalities themselves are not detrimental to the health of the child
  • minor abnormalities can be associated with major abnormalities, so act as a clue to investigate more serious underlying defects
  • the likelihood of having a major abnormality increases with the number of minor abnormalities that an individual has
    • e.g. ear anomalies are present in nearly all children with syndromic malformations
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6
Q

How can the developmental time period be split into 3 unequal parts based on fertilisation age?

A

Early development stage:

  • this is the period from week 0 - 3
  • it involves rapid cell division (cleavage) to form the morula, followed by the blastocyst

Embryonic period:

  • this describes the time period from week 3-8
  • it is also called the organogenesis period as it is the time during which body systems are being developed

Foetal period:

  • this describes the time period from week 8-38
  • there is maturation of structures that have formed during the organogenesis period
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7
Q

During which period of development is the foetus most susceptible to teratogens and why?

What happens if it is exposed to a teratogen before this period?

A
  • the foetus is most susceptible to teratogens during the embryonic period (weeks 3-8)
  • a congenital malformation is most likely to occur during this period as this is when organs and body systems are developing
  • a congenital malformation can occur outside of this period, but the risk is much lower
  • the foetus is also susceptible to teratogens during gastrulation period (weeks 0-3), but is more likely to spontaneously abort
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8
Q

What 5 types of anomaly fall under the term “congenital malformation”?

A
  • malformations
  • disruptions
  • deformations
  • syndromes
  • associations
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9
Q

What is meant by a malformation and when do they occur?

A
  • malformations occur during the formation of structures (e.g. organogenesis)
  • disturbed formation of a structure results in its complete or partial absence or an abnormal configuration
  • can be caused by environmental and/or genetic factors acting together or independently
  • e.g. complete/partial absence of a limb, ASD, VSD
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10
Q

What is meant by a disruption?

A
  • a disruption results in a morphological alteration of already formed structures due to a destructive process
  • e.g. amniotic bands causing limb defects or vascular accidents leading to transverse limb defects
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11
Q

What is meant by a deformation?

A
  • deformations result from mechanical forces that mold a part of the foetus over a prolonged period
  • e.g. clubfeet
  • they often involve the musculoskeletal system and are potentially reversible postnatally
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12
Q

What is meant by a syndrome?

A
  • a group of anomalies that are occurring together and have a specific common cause
  • e.g. Down’s syndrome, foetal alcohol syndrome
  • this term implies that a diagnosis has been made and the risk of recurrence is known
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13
Q

What is meant by an association?

A
  • the nonrandom appearance of 2 or more anomalies that occur together more frequently than by chance alone, but the cause has not been determined
  • e.g. VACTERL association
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14
Q

What happens in amniotic band syndrome?

What type of congenital malformation is this?

A
  • it is a disruption as it involves disturbance to a structure that has already started to form and develop normally
  • it is not a syndrome - a syndrome involves a group of phenotypic presentations occurring together and involving different systems
    • this only involves the limbs
  • fibrous bands of the amniotic sac become tangled around the developing foetus
  • this presents a serious risk if they wrap around the head or umbilical cord
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15
Q

What type of congenital malformation is produced from oligohydraminos and why?

A
  • oligohydraminos is the failure to form enough amniotic fluid
  • it can happen for many reasons, including problems with the development of the kidneys
  • it is associated with clubfoot and a slanted cranium as growth of the foetus is restricted due to lack of amniotic fluid
  • this is an example of a deformation as there is a physical force acting on the foetus (lack of space in amniotic sac)
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16
Q

What is meant by the principles of teratology?

A
  • how easily a given agent can cause a congenital defect depends on a number of factors
  • the factors determining the capacity of an agent to produce birth defects are the principles of teratology
  • they influence the teratogen’s ability to cross the placenta and cause a malformation
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17
Q

What are the 5 principles of teratology?

A
  1. genetics
  2. timing
  3. dose and duration
  4. mechanism of action
  5. manifestation of the abnormality that has been caused
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18
Q

How do genetics act as a principle of teratology?

A
  • susceptibility to teratogenesis depends on the genotype of the conceptus and the manner in which this genetic composition interacts with the environment
  • the maternal genome is also important with respect to:
  1. drug metabolism
  2. resistance to infection
  3. other biochemical / mechanical processes affecting the foetus

the ability of the placenta to filter out teratogens has a genetic influence

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19
Q

What is meant by timing as a principle of teratology?

A
  • the timing of exposure describes the point in development at which the foetus is exposed to the teratogen
  • the foetus is most susceptible to teratogens during the embryonic period (weeks 3-8)
  • some teratogens can affect the foetus outside of the organogenesis period - no stage of development is completely safe
  • each organ system may have 1 or more stages of susceptibility
    • e.g. cleft palate can occur at the blastocyst stage (day 6) or when the palatal shelves are forming (week 7) amongst others
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20
Q

What is meant by dose and duration as a principle of teratology?

A
  • this describes the quantity of teratogen** that the foetus is exposed to and the **duration of time that this exposure lasts for
  • the CNS develops for a long period of time, so these structures are susceptible to teratogens for the longest period of time
    • this is why the CNS (incl. eyes) are often involved in congenital malformations)
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21
Q

What is meant by mechanism of action as a principle of teratology?

A
  • teratogens act in specific ways on developing cells and tissues to initiate abnormal embryogenesis
  • this is often by switching genes on or off or by inducing / inhibiting enzymes
  • pathogenesis may involve cell death, decreased/increased cell proliferation or other cellular phenomena
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22
Q

What is meant by manifestation of the abnormality that has been caused as a principle of teratology?

A
  • this describes the effect of the teratogen
  • manifestations of abnormal development are:
  1. death
  2. malformation
  3. growth retardation
  4. functional disorders
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23
Q

What are the 8 major classes of teratogens?

A
  1. infectious agents
  2. heavy metals
  3. radiation
  4. drugs
  5. pyrexia / hyperthermia
  6. hormones
  7. maternal illness / disease
  8. maternal & paternal advanced age
  • heavy metals and radiation are grouped together as physical teratogens
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24
Q

What are the 5 major viruses that can cross the placenta and what birth defects are they associated with?

A

Rubella:

  • causes congenital rubella syndrome that leads to deafness, cataracts and heart defects

Cytomegalovirus:

  • often the mother has no symptoms, but can cause serious illness of the foetus at birth and can be fatal
  • some infants are asymptomatic at birth but develop abnormalities later in life:
  1. hearing loss
  2. visual impairment
  3. cerebral calcifications (calcium deposits within neural tissue)
  4. intellectual disability

Herpes simplex:

  • usually infection is transmitted during delivery, causing severe illness and death
  • infection during pregnancy can cause microcephaly and microphthalmia

Varicella:

  • associated with:
  1. scarring of the skin
  2. limb hypoplasia
  3. intellectual impairment
  4. defects of the eyes and CNS

Toxoplasmosis:

  • associated with hydrocephalus and cerebral calcifications
25
Q

What steps should a pregnant woman take to avoid toxoplasmosis infection?

A
  • they are advised to avoid undercooked meat and cat litter as these carry the parasite Toxoplasmosis gondii
  • this can only harm the baby if it is contracted during pregnancy
  • if the woman is already infected with the parasite prior to becoming pregnant, this should not cause any problems
26
Q

What is the importance of hyperthermia/pyrexia as a teratogen and what steps should be taken to avoid this?

A
  • heat can affect formation of the neural tube and can result in the formation of neural tube defects
  • pregnant women are advised to avoid hot tubs and saunas
  • pyrexia is an increased temperature that results from the pregnant woman fighting an infection, and this can also affect neurulation
27
Q

What are the 7 main drugs that are known to cross the placenta and cause birth defects?

What needs to be taken into account when considering a mother’s medication?

A
  1. thalidomide
  2. anti-epileptics
  3. isotretinoin
  4. anti-psychotics & anxiolytics
  5. antidepressants (SSRIs)
  6. warfarin
  7. ACE inhibitors
  • it is important to balance both the health of the mother and foetus when advising about medications
28
Q

What malformations are associated with thalidomide?

A
  • it was used as an antinauseant and sleeping pill
  • it has been linked to amelia and meromelia (complete or partial absence of the extremities)
  • it is also associated with:
    • NTDs
    • orofacial clefts
    • intellectual disability & autism
    • heart defects
    • defects of the urogenital and gastrointestinal systems
29
Q

What malformations are anti-epileptics associated with?

A
  • congenital heart defects
  • cleft palate
  • valproic acid increases the risk of ASDs, polydactyly, hypospadius and craniosynostosis and spina bifida (highest risk)
30
Q

What defects are caused by anti-psychotics and anxiolytics?

A
  • certain defects are suspected but no links are proven:
  1. limb/skeletal malformations
  2. CNS defects
  3. cleft palate
  4. congenital heart defects
31
Q

What congenital malformations are linked to SSRIs and why?

A
  • congenital heart defects
  • increase in frequency of spontaneous abortions
  • they inhibit serotonin signalling, which is important for establishing laterality and for heart development
32
Q

What defects is isotretinoin associated with?

A
  • congenital heart defects
  • severe limb malformations
  • this is usually prescribed for acne and chronic dermatoses, but it is highly teratogenic and can produce virtually any type of malformation
33
Q

What defects is warfarin associated with?

A
  • skeletal abnormalities including:
  1. nasal hypoplasia
  2. abnormal epiphyses in the long bones
  3. limb hypoplasia
34
Q

What defects are ACE inhibitors associated with?

A
  • growth retardation
  • foetal death
  • renal dysfunction
  • oligohydraminos
35
Q

What are the proposed mechanisms of action of thalidomide?

When might it still be prescribed?

A
  • inhibition of angiogenesis (formation of vascular structures)
  • induction of oxidative stress (within the mitochondria)
  • decreased expression of FGF genes
  • induction of cell death
  • it is no longer prescribed for morning sickness, but is still prescribed to treat leprosy in countries (e.g. Brazil) where the incidence is higher
36
Q

What are the potential malformations associated with cigarette smoking?

A
  • it has been linked to increased risk of orofacial clefts
  • it also contributes to intrauterine growth retardation and premature delivery
37
Q

How does the amount of alcohol consumed during pregnancy relate to the severity of malformation?

A

the concentration of alcohol consumed during pregnancy is correlated with the severity of phenotypic presentations at birth

  • the more alcohol that is consumed during pregnancy, the more severe birth defects produced
38
Q

What is the advice given to mothers relating to alcohol consumption?

A
  • if you are pregnant or planning a pregnancy, the safest approach is not to drink alcohol at all to keep the risks to the baby to a minimum
  • the risk of harm is likely to be low if a woman has only drunk small amounts before finding out she is pregnant
  • women who find out they are pregnant after already drinking during pregnancy should avoid further drinking
39
Q

What is the difference between foetal alcohol spectrum disorder (FASD) and foetal alcohol syndrome (FAS)?

A
  • alcohol can induce a broad spectrum of defects ranging from intellectual disability to structural abnormalities of the face, heart and brain
  • FASD is used to refer to any alcohol-related defects
  • FAS is the most severe end of the spectrum and includes structural defects, growth deficiency and intellectual disability
40
Q

What is the spectrum of malformations associated with FAS?

A
  1. growth restriction
  2. intellectual disability
  3. behavioural problems
  4. facial abnormalities
  5. heart defects
  6. brain defects (e.g. microcephaly)
41
Q

What are the facial abnormalities associated with FAS?

A
  1. smooth philtrum
  2. thin upper lip
  3. flat nasal bridge
  4. flat midface
  5. epicanthal folds
  6. short palpebral fissures
42
Q

How is alcohol able to act as a teratogen?

A
  • ethanol diffuses through the placenta and enters the foetal compartment to accumulate within the amniotic fluid
  • the baby will ingest the amniotic fluid, swallow it and digest it and then release it back into the amniotic sac as well as breathing it in
43
Q

By what mechanisms is ethanol thought to act as a teratogen?

A
  • through generation of reactive oxygen species / oxidative stress
  • damaging effects on the placenta through vessel vasoconstriction
    • this means that not enough nutrients are reaching the foetus - leading to growth restriction and intellectual disability
  • mitochondrial damage
  • disruption of normal cell-cell adhesion
  • epigenetic effects
44
Q

What is the recommendation for the use of ionising radiation in healthcare?

A
  • all patients, but especially those who are young and of child bearing age, should not be exposed to ionising radiation unless completely necessary
  • especially for the abdomen and pelvis
  • a pregnancy test is commonly performed on women prior to exposure to ionising radiation even if they state they are not pregnant
  • staff must wear lead aprons and protect the thyroid
45
Q

How does radiation act as a teratogen?

A
  • it kills rapidly proliferating cells
  • this allows it to produce virtually any type of birth defect depending upon the dose and stage of development of the foetus
  • it also acts as a mutagenic agent and can lead to genetic alterations of germ cells and subsequent malformations
46
Q

What are the main sources of ionising radiation in health care?

Which has a higher radiating dose?

A
  • X-ray is a source of ionising radiation through:
  1. plain films
  2. fluoroscopy
  3. barium studies
  • CT scans have a higher radiating dose than X-ray
  • With CT scans, exposure increases with contrast agent
47
Q

How can androgenic agents (hormones) act as teratogens?

A
  • androgenic agents were used in pregnancy to prevent abortion (progestins)
  • they cause masculisation of female genitalia through fusion of the labia and enlargement of the clitoris
48
Q

How can synthetic oestrogens cause congenital malformations?

A
  • they can lead to female tract malformations and can affect the formation of the uterine tubes
    • this can lead to reproductive dysfunction in later life
  • also assoiated with congenital malformations of the uterus and upper vagina
  • there is also an increased risk of carcinoma of the cervix and vagina in later life
49
Q

How do environmental oestrogens cause congenital malformations?

A
  • these are thought to be linked to a decreased sperm count and increased incidence of malformations of male genitalia
  • an increased amount of soya in a males diet is thought to increase levels of oestrogens
  • they also increase incidence of testicular cancer, hypospadias and CNS abnormalities
50
Q

How is cortisone linked to congenital malformations?

A
  • there is an association between increased levels of cortisone and an increased risk of oro-facial clefts
  • women who take corticosteroids during pregnancy may be at a higher risk of having a child with an orofacial cleft
51
Q

How is maternal diabetes linked to congenital malformations?

A
  • in diabetes, there is an inability to monitor the levels of sugars that are crossing the placenta
  • this can lead to a wide variety of defects, including NTDs, caudal dysgenesis** and **heart defects
  • it is also linked to a high incidence of stillbirths, neonatal deaths and abnormally large infants
52
Q
A
53
Q

How can the risk of congenital malformations in a pregestational diabetic be lowered?

A
  • glucose levels play a role in formation of congenital malformations, and not insulin
  • there is a correlation between the severity and duration of maternal disease and incidence of malformations
  • strict control of maternal glucose levels before conception and throughout pregnancy can reduce the occurrence of malformations
54
Q

How can obesity lead to an increased risk of congenital malformations?

A
  • prepregnancy obesity is associated with a 2x increased risk of a child with an NTD
  • this is thought to be due to maternal metabolic disturbances affecting glucose, insulin and other factors crossing the placenta
  • obesity is also associated with increased risk of omphalocele and heart defects
55
Q

What is the major nutritional deficiency associated with congenital malformations?

A
  • folic acid is important in neurulation and deficiency can result in NTDs
56
Q

What are the potential paternal disease / factors that are linked to increased risk of congenital malformations?

A

occupational / environmental exposure:

  • exposure to heavy metals and cigarette smoke has been linked to:
  1. low birth weight
  2. spontaneous abortion
  3. birth defects (via germ cell mutations)

increasing age:

  • both increasing age and younger age are associated with increased chance of birth defects

semen contamination:

  • this describes certain factors entering the ejaculate and causing malformations within the sperm themselves
57
Q

What heavy metals have been seen to act as teratogens?

A
  • lead and mercury are able to cross the placenta and act as teratogens
  • lead is associated with increased abortions, growth retardation and neurological disorders
  • a diet high in fish (especially tuna) contains a lot of mercury, and whilst the mother may not have any symptoms, the foetus is susceptible to mercury
58
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Embryology (20 decks)

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