Teratology

1. EMBRYOLOGY:
TERATOLOGY
Mohamad Aris Mohd Moklas (PhD)

2. The science that studies the causes of structural,
functional, behavioral & metabolic disorders
present at birth:
- size,
- arrangement or
- composition of any organ or part of the body.
Teratology

3. Principles of teratology
1. Susceptibility to teratogenesis depends on the genotype of the
fetus & mother.
2. Susceptibility to teratogens varies with the developmental stage
at the time of exposure. The most sensitive period for inducing
birth defects is the 3rd – 8th weeks of gestation, the period of
embryogenesis or organogenesis.
Teratology

4. Principles of teratology
3. Manifestations of abnormal development depend on dose and
duration of exposure to a teratogen.
4. Teratogens act in specific ways on developing cells & tissues to
initiate abnormal embryogenesis.
Teratology

5. Teratology

6. Types of anomalies
a) Visible deviations of structure
b) Non-visible deviation or deviations of function
occurring as a result of enzyme deficiency which result in abnormal
chemical functions called ‘inborn errors of metabolism’ involving
protein, carbohydrates, lipids & pigments.
a) Anomalies existing at birth or long before birth – such are called
congenital anomalies.
Teratology

7. Incidence
a) The incidence of congenital anomalies vary with race & also
in different populations of the same race.
b) Some anomalies are more common in males such as pyloric
stenosis, cleft lip & hydrocephalus; and some anomalies are
more common in females such as congenital dislocation of
the hip, birth marks, anomalies of brain and spinal cord.
Teratology

8. Frequency of congenital anomalies
a) Muscular-skeletal - 38 %
b) Integumentary - 20 %
c) CNS - 14 %
d) GIT - 9 %
e) Genito-urinary - 9%
f) Respiratory - 2 %
Teratology

9. Classification of anomalies
(1) Failure of development: Agenesis
- an organ or body part may be subjected to developmental failure
Teratology

10. Classification of anomalies
(1) Failure of development: Agenesis
Teratology
Scrotum agenesis

11. Classification of anomalies
(2) Incomplete development
- In growth: dwarfism, gigantism
- In union: cleft palate, double uterus
- In subdivisions: heart chambers, body cavities, double ureters, multiple
kidneys, double gall bladders
- In metabolism: sickle cell anaemia
- In histological differentiation: thickened skin, stenosis
- In number: multiple digits, multiple nipples, twinning
Teratology

12. Classification of anomalies
(2) Incomplete development
Teratology
Gigantism & dwarfism Multiple breast syndrome

13. (3) Embryonic persistence - any embryonic
structure which persist instead of disappearing
- Meckel’s diverticulum
- cervical cyst
- thyroglossal cyst
Classification of anomalies
Teratology

14. (3) Embryonic persistence
- Meckel’s diverticulum
Classification of anomalies
Teratology

15. (4) Misplacements – ectopic thyroid, ectopic
pregnancy, ectopic testes
Classification of anomalies
Teratology

16. (4) Misplacements –
- ectopic thyroid
Classification of anomalies
Teratology

17. The modern view on anomalies is based on two causal factors:-
1.Hereditary
2.Environment
Teratology
Classification of anomalies

18. 1.Hereditary
(1) Genes
– autosomal (dominant or recessive); X-linked (dominant or recessive)
(2) Chromosomes
- Non-disjunction (failure of chromosome pairs / chromatids to separate properly
during cell division.
- Eg: Turner’s syndrome (X monosomy) (45, X0) & Down’s syndrome (Trisomy 21)
Teratology
Classification of anomalies

19. 2. Environment or teratogenic agents
- Environmental factors cause 7 to10 % of congenital anomalies.
(1) Physical : external traumatic injuries
(2) Irradiation: X rays or atomic explosions
(3) Chemical agents:
Drugs (thalidomide, anti-convulsants, social drugs)
Alcohol (alcohol fetal syndrome)
Teratology
Classification of anomalies

20. 2. Environment or teratogenic agents
(4) Hormones: thyroxine, diabetic mothers
(5) Heavy metals:
Mercury (mental retardation)
Lead (increased abortion, fetal anomalies, functional deficit etc)
(6) Growth inhibitors: nitrogen mustard
(7) Vitamin deficiency
Teratology
Classification of anomalies

21. 2. Environment or teratogenic agents
(8) Infectious agents: German measles, cytomegalovirus, syphilis, HIV,
herpes simplex
(9) Antigens: Rh factor in mother can pass through the placenta to the foetus
and produce malformed fetal blood cells
(10) Cigarette smoking: intra-uterine growth retardation (small infants)
Teratology
Classification of anomalies

22. Polydactyly
Meromelia
Amelia
Down’s Syndrome

23. Holoprosencephaly
Caudal dysgenesis
Anencephaly
Cleft lip