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Reproductive Anatomy > Teratogenesis and Abnormal Differentiation > Flashcards

Teratogenesis and Abnormal Differentiation Flashcards

1
Q

What is a birth defect?

A

any anomaly (functional or structural) that presents in infancy or later in life and is caused by events preceding birth, whether inherited, or acquired

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2
Q

What is teratology?

A 
Study of abnormal development 
- Causes,
- Mechanisms 
- Pattern of abnormal development
Concept: certain developmental stages are more vulnerable to disruption than others
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3
Q

What are the 4 clinically significant types of congenital anomaly?

A
  1. malformation
  2. disruption
  3. deformation
  4. dysplasia
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4
Q

What is malformation?

A

Morphological defect of an organ or part of an organ that results from an intrinsically abnormal developmental process

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5
Q

What is a disruption?

A

Morphological defect of an organ or part of an organ that results from extrinsic factors
e.g. exposure to teratogens such as drugs and viruses

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6
Q

What is a deformation?

A

An abnormal form, shape, or position of part of the body that results from intrauterine mechanical forces
e.g. equinovarus foot or club foot due to oligohydramnios

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7
Q

What is dysplasia (dyshistogenesis)?

A

An abnormal organization of cells into tissues and its morphological results

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8
Q

What are the main causes of birth defects?

A
  1. Genetic factors – chromosomal abnormalities
  2. Environmental factors
    - Genetic and Environmental Factors act as Determinants of Susceptibility to Disease Initiated during Development
  3. Social factors
  4. Multifactorial inheritance
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9
Q

What 2 changes occur in chromosomal complements?

A
  1. Numerical change

2. Structural change

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10
Q

What do the changes in chromosomal complements affect?

A
  1. Sex chromosomes

2. Autosomal chromosomes

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11
Q

Describe the 3 classes of numerical chromosomal abnormalities?

A
  1. Polyploidy – extra copies of all chromosomes
    e. g triploidy, tetraploidy
    - multiples of haploid number of 23 other than diploid number (46) e.g. 69
  2. Aneuploidy – loss or gain of only certain chromosomes
    e. g trisomy 21 or monosomy (missing a chromosome , 45, X)
  3. Mixoploidy – two or more cell lines which differ in chromosomal number
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12
Q

Aneuploidy results from?

A
  1. nondisjunction
    – failure of a chromomal pair or two chromatids of chromosome to disjoin during mitosis and meiosis
  2. anaphase lag
    – chromosome moves so slowly to the pole that it does not get incorporated into the nucleus as it forms in telophase
    - May occur during paternal or matermal gametogenesis
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13
Q

What does mixoploidy produce?

A
  1. Mosaicism - two or more genetically different cell lines all derived from a single zygote
  2. Chimerism - two or more genetically different cell lines originating from different zygotes
    - organism derived from different zygotes
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14
Q

What are the different types of aneuploidy?

A
  1. Hyperdiploidy - e.g. Trisomy 47, XX, + 21 (Down’s syndrome)
  2. Hypoploidy - e.g. Monosomy 45, X (Turner syndrome)
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15
Q

Describe Turner syndrome (45,X)?

A

Definition: Monosomy x, chromosome abnormality
Cause: nondisjunction during gametogenesis
- 85% - paternal X is missing
Mortality: 1% survive
Phenotype: female
Clinical presentation: Secondary sex development do not develop

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16
Q

What is trisomy?

A

presence of three homologous chromosomes instead of a pair
- Caused by meiotic nondisjunction of chromosomes (gametes with 24 instead of 23 chromosomes)
Note: Errors in meiosis, increases with maternal age

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17
Q

Trisomy is associated mainly with which 3 syndromes?

A
  1. Trisomy 21 or Downs syndrome
  2. Trisomy 18 or edwards syndrome
  3. Trisomy 13 or Patau syndrome
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18
Q

Describe the clinical presentation of Trisomy 21 (Downs)?

A
  1. Hand - Single transverse crease
  2. Clinodactyly (curved 5th digit)
  3. Up-slanting palpebral fissures
  4. Epicanthal folds
  5. Flat nasal bridge
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19
Q

Describe the clinical presentation of Trisomy 18 (Edwards)?

A
  1. Growth retardation
  2. Clenched fists
  3. Short sternum
  4. Narrow pelvis
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20
Q

Describe the clinical presentation of Trisomy 13 (Patau)?

A
  1. Bilateral cleft lip
  2. Low-set malformed ear
  3. Small omphalocele
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21
Q

What is Trisomy of sec chromosomes?

A

Sex chromatin studies show two masses of sex chromatin

- common condition

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22
Q

What are the 3 syndromes of Trisomy of sex chromosomes?

A
  1. 47, XXX : female > normal, fertile slightly mentally retarded
  2. 47, XXY : Male > Klinefelter syndrome
  3. 47, XYY : Male > normal, tall, aggressive
23
Q

Describe the clinical presentation of 47,XXY trisomy?

A
  1. Gynecomastia - presence of breasts (40%)
  2. Tall - long lower limbs
  3. Small testes - hyalinization of seminiferous tubules
  4. Aspermatogenesis
  5. Less intelligent
24
Q

What are structural chromosome abnormalities?

A

Result from chromosomal breakage and reconstitution in an abnormal combination

25
Q

What causes structural chromosomes abnormalities?

A

environmental factors

  1. Drugs,
  2. radiation
  3. chemicals
  4. viruses
26
Q

What happens to the structure of the chromosome to cause abnormalities?

A 
Deletion
Inversion
Duplication
Insertion
Ring
Marker
Translocation, reciprocal;
Translocation, Robertsonia
27
Q

Describe the abnormalities caused by microdeletions and micro-duplications?

A

Deletions and duplications that span several contiguous genes cause contiguous gene syndromes

  1. Prader-Willi syndrome (PWS) – associated with short stature, mild mental retardation, obesity, hyperphagia (overeating), hypogonadism
  2. Angel-man syndrome (AS) – associated with severe mental retardation, microcephaly, brachycephaly (shortness of head)
28
Q

Describe anomalies caused by mutant genes?

A

Gene defects involves loss of or change in function
- Most mutations are deleterious and some are lethal

  1. Achondroplasia – mutations in FGFR3 gene on chromosome 4p.
  2. Fragile X syndrome – X- linked disorder ass. With mental impairment
29
Q

Describe the clinical presentation of achondroplasia?

A 
Short stature
Short limbs and fingers
Normal length of trunk
Large head
Depressed nasal bridge
30
Q

Describe the clinical presentation of Fragile X syndrome?

A

Normal appearance
Mentally retarded
Long face
Strabismus (crossed right eye)

31
Q

What are teratogenes?

A

environmental agents that can produce a congenital anomaly or raise the incidence of anomaly in a population
- 7-10% of anomalies are caused by teratogenes
e.g. drugs infections
Note: The organs and body parts are the most sensitive to teratogenic agents

32
Q

What are the 3 basic principles of teratogenesis?

A
  1. Critical periods of development
  2. Dosage of drug or chemical
  3. Genotype of the embryo
33
Q

The most critical periods in development are when which stages are at their peak?

A
  1. cell division
  2. Cell differentiation
  3. Morphogenesis
34
Q

What happens when teratogenes act on a week old embryo?

A

kills the embryo

35
Q

What happens when teratogens act on the embryonic period (3 - 8 weeks)?

A

disrupts organogenesis
- male foration of embryo may occur
e.g. heart defect
Note: period of maximal sensitivity to abnormal development

36
Q

What happens when teratogens act on the fetal period (8 - 38 weeks)?

A

Late developing organs are disrupted e.g. ears

  • functional disturbance of fetus may occur
    e. g. mental retardation
37
Q

Describe the critical disruption period of brain development?

A

from 3-16 weeks

- teratogens (e.g. alcohol) may cause mental retardation

38
Q

What is the critical disruption point of tooth development?

A

6 weeks and continues long after birth

- Tetracyclines disrupts permanent tooth development from 18 weeks (prenatal) to 16 years

39
Q

Describe the critical disruption period of the skeletal system?

A

prolonged period into childhood

40
Q

Describe the Principles of Developmental Toxicity: Toxic Window?

A

Expected incidence of malformation of different organs and systems, the susceptibility of which varies according to the days of gestation

41
Q

Describe the conditions in which teratogens can affect different systems at the same time?

A
  1. High levels of Radiation - Affect CNS and eyes
  2. Toxoplasma gondii - affects brain and eyes
  3. Rubella virus - cause eye defects (glucoma, cataracts) deafness, and cardiac anomalies
  4. Thalidomide (sedative drug) - induces limb defects (meromelia)
42
Q

How does the genotype of the embryo affect the response to teratogens?

A

There is genetic differences in response to a teratogen

e. g. 5-10% of embryos exposed to phenytoin (anticonvulsant drug) develop fetal hydantion syndrome
- More than ½ are unaffected.

43
Q

For a drug to be considered as a teratogen what must happen?

A
  1. Dose - response relationships to be observed
    - Drugs vary considerably in their teratogenecity
  2. The greater the exposure during pregnancy, the more severe the phenotypic effects
44
Q

What are the consequences of fetal alcohol spectrum disorder?

A 
Miscarriage
Preterm birth
Low birth weight
FAS
ARBD - alcohol-related birth defects
ARND - alcohol-related neurodevelopmental disorders
Birth complications
45
Q

What is diethylystilbestrol (DES)?

A

a potent estrogen

- Given to about 4.8 million pregnant women to prevent miscarriage

46
Q

Describe the effects of in utero exposure of DES on female progeny?

A
  1. Vaginal cancer in young women (1.4/1,000–10,000)

2. Reproductive problems (18%)

47
Q

Describe the effects of DES in utero exposure on human male progeny ?

A

3 times normal incidence

  1. Anatomic abnormalities of the reproductive tract
  2. Altered semen - including decreased sperm density, count, and motility
48
Q

Describe the teratogenesis and abnormal differentiation caused by tetracyclines?

A

Cross placenta and are deposited into embryo bones and teeth
Cause:
- yellow staining of deciduouds and permanent teeth
- enamel hypoplasia
- diminished growth of long bones.

49
Q

Describe the abnormal differentiation caused by Streptomycin and dihydrostreptomycin (antituberculosis agent)?

A

causes deafness in infants

50
Q

Name anticonvulsants with teratogenic effects?

A
  1. trimethadione-tridione
  2. phenytoin
  3. vaproic acid
    - treatments for epilepsy
51
Q

Describe the abnormal differentiation caused by anticonvulsants?

A
  1. trimethadione-tridione - Causes growth retardation, developmental delay, V-shaped eyebrows, low-set ears, cleft lip, cardiac , genital urinary and limb defects
  2. Phenytoin - causes fetal hydantion syndrome microcephaly
  3. Vaproic acid - causes craniofacial and neural tube defects
52
Q

Describe the teratogenesis and abnormal differentiation caused by anticoagulants?

A

Cross placenta except herparin.
Causes CNS defects , hypoplastic nasal cartilage, stipled epiphyses
e.g. Warfarin and coumarin derivatives

53
Q

Name preventable birth defects and how they can be prevented?

A
  1. neural defects - folic acid
  2. congenital syphilis - safe sex prior to conception/treatement
  3. congenital HIV - safe sex prior to conception/avoid risks
  4. congenital rubella syndrome - immunization
  5. Rh diseases - immunoglobin
  6. fetal alcohol syndrome - avoid alcohol

Reproductive Anatomy (16 decks)

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