TERATOGENS

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MBBSPROGRAMGDA MODULE

• DEPARTMENT OF ANATOMY
• TERATOGENS CONGENITAL ANOMALIES
• Presented By
• PROF / YOUSRY M SHAWKY

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TERATOGENS CONGENITAL ANOMALIES

• TERATOLOGY
  It is the study of abnormal development.
• TERATOGEN
  Any agent that can produce congenital
  anomaly.
• CONGENITAL ANOMALY
  It is a structural abnormality of any organ
  that is present at birth.

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CAUSES OF CONGENITAL ANOMALIES

• I) Genetic factors such as
• - Numerical chromosomal abnormalities
• Structural chromosomal abnormalities
• Abnormalities caused by mutant genes
• II) Environmental (Teratogenic) factors such as
• Drugs
• Infectious agents
• Chemicals
• Ionizing radiation
• Maternal diseases

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(I) ANOMALIES CAUSED BY GENETIC FACTORS

• A) Numerical Chromosomal abnormalities
• The normal human cell contains 46 chromosomes
  - 44
  autosomes
  - 2 sex chromosomes (XX in female XY in
  male).
• 1) Monosomy (45 chromosomes)
• For example
• Turner syndrome (44X)
  Absent 2nd X chromosome. The 2ry sexual
  characters do not develop in 90 of girls with
  Turner syndrome, necessitating hormone
  replacement therapy.

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• 2) Trisomy (47 chromosomes) It is due to meiotic
  nondisjunction of chromosomes resulting in a
  gamete with 24 instead of 23 chromosomes and
  subsequently in a zygote with 47 chromosomes. It
  may affect sex chromosomes or autosomes e.g.
• Down syndrome or trisomy 21 trisomy 13

Female neonate with trisomy 13 note cleft lip
palate, polydactyly (excess finger) umbilical
hernia
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• Down syndrome or trisomy 21
• Physical characteristics
• oblique eye fissures with small skin folds on the
  inner corner of the eyes.
• muscle hypotonia, a flat nasal bridge, a single
  palmar fold (simian crease), a large and
  protruding tongue, a short neck, white spots on
  the iris.
• congenital heart defects, excessive space between
  large and second toe, and a single flexion furrow
  of the fifth finger.
• mental retardation
• Abnormalities affecting any body system.

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• 3) Tetrasomy pentasomy of sex chromosomes
• In females
• 48(44,XXXX) 49(44,XXXXX).
• In males
• 48(44,XXXY, 48(44,XXYY), 49(44,XXXXY)
  49(44,XXXYY).

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• B) Structural chromosomal abnormalities
• It results from chromosome break down followed
  by reconstitution in abnormal combination
• Translocation It is the transfer of a piece of
  one chromosome to a nonhomologous chromosome. It
  does not necessarily produce abnormal
  development.
• Deletion When a chromosome breaks a portion may
  be lost. For example deletion from chromosome 5
  causes cri du chat syndrome (the infant produces
  catlike cry at birth).

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• C) Anomalies caused by mutant genes
• It result from permanent heritable changes in the
  sequence of genomic DNA, For example
  achondroplasia
• The patient shows
• Short stature
• Short limbs, fingers toes.
• Large head, with depressed nasal bridge
  prominent forehead.
• Normal length of the trunk.

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(II) ANOMALIES CAUSED BY TERATOGENIC
(ENVIRONMENTAL) FACTORS

• Teratogens known to cause birth defects
• Drugs For example a) Alcohol
  
• Produces Fetal Alcohol Syndrome (FAS)
• the infant has
• - Microcephaly
• - Narrow palpebral fissure
• - Mental growth retardation.
• - Big tongue depressed nasal bridge

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• b) Thalidomide
• Produces limb defects as Meromelia (small limb)
  Amelia (absent limb).
• c) Androgens
• They affect female fetus producing
  masculinization of the external genitalia
  resulting in
• Enlarged clitoris
• Fused labia majora

Clitoris
Labia majora
Meromelia
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• 2) Infectious agents
• a) Viruses
• - Rubella (German measles) virus may result in
  congenital cataract or glaucoma
• Herpes simplex human immuno-deficiency virus
  (HIV) cause birth defects
• b) Bacteria e.g. spirochetes may cause
  congenital syphilis
• c) Parasites e.g. toxoplasmosis may cause birth
  defects.

Cataract
Glaucoma
Spirochetes
Toxoplasmosis
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• 3) Chemicals
• Heavy metals for example methyl mercury may
  result in cerebral atrophy mental retardation.
• 4) High level of ionizing radiation
• May result in microcephaly mental retardation.
• 5) Maternal diseases e.g. diabetes mellitus

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THANK YOU