Teratology Causes of congenital malformations



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Teratology

  • Teratology

  • Causes of congenital malformations:

  • (a) Genetic factors: chromosomal abnormalities

  • (b) Environmental factors: drugs, viruses

  • Types of chromosomal abnormalities:

  • (a) Numerical

  • (b) Structural





Changes in the number of chromosomes:

  • Changes in the number of chromosomes:

    • Polyploidy
    • Aneuploidy (Heteroploidy)
      • Deviation from the diploid number of chromosomes
      • 2n + 1, 2n -1 etc.


Failure of pulling apart of 2 chromatids to opposite ends after metaphase stage of mitosis.

  • Failure of pulling apart of 2 chromatids to opposite ends after metaphase stage of mitosis.

  • Reduplication of chromosomes without dissolving of nuclear membrane.

  • Failure of cytoplasmic division.



Autopolyploidy: even-numbered multiples of haploid number of chromosomes. e.g.-

  • Autopolyploidy: even-numbered multiples of haploid number of chromosomes. e.g.-

  • (a) Tetraploidy (23x4 or 92 chromosomes)

  • (b) Hexaploidy (23x6 or 138 chromosomes)

  • (c) Octaploidy (23x8 or 184 chromosomes)

  • etc.



2. Allopolyploidy: odd-numbered multiples of haploid number of chromosomes. e.g.-

  • 2. Allopolyploidy: odd-numbered multiples of haploid number of chromosomes. e.g.-

  • (a) Triploidy (23x3 or 69 chromosomes)-commonest

  • (b) Pentaploidy (23x5 or 115 chromosomes)

  • (c) Heptaploidy (23x7 or 161 chromosomes)

  • etc.



Non-dysjunction: failure of separation of chromosomes during cell division.

  • Non-dysjunction: failure of separation of chromosomes during cell division.

  • Formation of 2 types of gametes (both abnormal)

  • Fusion of either of these abnormal gametes with a normal gamete can result in trisomy or monosomy

  • May involve autosomes or sex chromosomes





Presence of 3 copies of a chromosome

  • Presence of 3 copies of a chromosome

  • Trisomy of Autosomes (13,18,21)

  • Trisomy of Sex Chromosomes (XXX, XXY)



Trisomy 13 or D-trisomy (Patau syndrome)

  • Trisomy 13 or D-trisomy (Patau syndrome)

  • Trisomy 18 or E-trisomy (Edward syndrome)

  • Trisomy 21 or G-trisomy (Down syndrome)



1st described by Bartholin (1657) & redefined by

  • 1st described by Bartholin (1657) & redefined by

  • Patau (1960).

  • Chromosomal complement: 47,XX,+13 (female) or

  • 47,XY,+13 (male)

  • Phenotype: Male or female

  • Incidence: 1:12,000 (increases with the age of

  • mother)



Mental deficiency

  • Mental deficiency

  • Low birth weight

  • Abnormal development

  • of frontal lobe

  • Absence of corpus callosum

  • Hypoplasia of cerebellum

  • Sloping forehead

  • Scalp defects







Chromosomal complement: 47,XX,+18 (female) or

  • Chromosomal complement: 47,XX,+18 (female) or

  • 47,XY,+18 (male)

  • Phenotype: Male or female

  • Incidence: 1:8000



Mental deficiency





Chromosomal complement: 47,XX,+21 (female) or

  • Chromosomal complement: 47,XX,+21 (female) or

  • 47,XY,+21 (male)

  • Phenotype: Male or female

  • Incidence: 1:800 (increases with the age of

  • mother)



Short height

  • Short height

  • Severe mental deficiency with decline in the IQ with age

  • Brachycephaly with flat face and occiput

  • Flat and low nasal bridge

  • Upward slant to palpebral fissures











1. Essentials of Anatomy for Dentistry Students,1st Edition.

  • 1. Essentials of Anatomy for Dentistry Students,1st Edition.

  • 2. Langman’s Medical Embryology,11th Edition.

  • 3. Human Embryology, 5th Edition.



1. Patau syndrome is associated with trisomy of chromosome:

  • 1. Patau syndrome is associated with trisomy of chromosome:

  • a) 13

  • b) 15

  • c) 18

  • d) 21



2. Rocker-bottom heel is associated with:



3. Brushfield spots is a characteristic feature of:

  • 3. Brushfield spots is a characteristic feature of:

  • a) Patau syndrome

  • b) Edward syndrome

  • c) Down syndrome

  • d) None of the above



4. All of the following are trisomy of autosomes except:

  • 4. All of the following are trisomy of autosomes except:

  • a) Edward syndrome

  • b) Klinefelter syndrome

  • c) Down syndrome

  • d) Patau syndrome



5. All of the following are examples of autopolyploidy except:

  • 5. All of the following are examples of autopolyploidy except:

  • a) Triploidy

  • b) Tetraploidy

  • c) Hexaploidy

  • d) Octaploidy




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