Previous sessions: discussed normal embryonic and
fetal development.
Unfortunately, things don't always go right.
More than 150,000 children born each year
with congenital malformations or birth
defects.
They are present in 2 to 3% of newborn
infants, and later become apparent in 2 to
3% of children. Thus, they affect
approximately 5% of the population
More than 4,000 different forms of birth defects known
Can affect any organ
and
Often affect multiple organs
Range: mild
Syndactyly
moderate
Encephalocele
severe
Syncephalus/Janiceps
From: March of Dimes
Defects of heart and blood vessels:
Aortic coarctation
Cerebral aneurysm
Patent ductus
arteriosus
Tetrology of Fallot
Valve stenosis
Defects of urinary system/genitalia
Extrophy of bladder
Hypospadias
Wilm’s tumor or
Nephroblastoma
Stenosis of ureter
Defects of face:
Goldenhar Syndrome
Cleft lip & palate
Occulofacial dysplasia
Hirsuitism
Defects of brain and/or spinal cord:
Spina bifida
Anencephaly
Rachischisis
Hydrocephalus
Defects of limbs:
Meromelia
Bifurcation of hand
Supernumary arm
Syndactyly
Polydactyly
The earlier in development that problems develop,
the more severe the birth defects will be
Many possible causes:
Chromosomal/genetic abnormalities
Drugs taken by mother which cross placenta
Infections of mother which cross placenta
Antibodies produced by mother
Environmental agents
Injury to fetus or during birth
However, cause is unknown ~ half the time
Chromosomal abnormalities:
Either: Wrong number of chromosomes
One or more abnormal chromosomes
Since all cells of all organs
have same chromosomes,
chromosomal abnormalities
often affect many different
organs
Chromosomal abnormalities:
Trisomy 21, or Down's Syndrome
~ 1 out of 660 live births
Abnormalities of face,
Abnormalities of hands, feet
Heart defects
Deafness
Usually marked cognitive and
intellectual impairment
Chromosomal abnormalities:
Trisomy 18, or Edward's Syndrome
~ 1 out of 3,000 live births
Most fetuses die in utero; Half of live births die < 2 weeks
Survival > 20 years rare
Abnormal face,
Abnormal hands, feet
Heart defects
Kidney defects
Marked cognitive and
intellectual impairment
Chromosomal abnormalities:
Trisomy 13, or Patau Syndrome
~ 1 out of 10,000 live births
Most fetuses die in utero;
80% of live births die in first year
Survival > 20 years very rare
Abnormal head and face,
particularly eyes and palate
Abnormal hands, feet
Heart defects
Kidney defects
Very severe cognitive and
intellectual impairment
Chromosomal abnormalities:
Turner's syndrome: X~ 1 out of 1500 live female births
Short female;
Poorly developed sexual
characteristics
Never enters puberty
therefore sterile.
Defects in heart, lungs,
vessels, bones
Occasionally cognitive
and intellectual
impairment
Chromosomal abnormalities:
Abnormality (missing piece) of chromosome #5
Cri du chat syndrome
Abnormal cry
Small head & face
Eye abnormalities
Damage to brain
Marked cognitive and
intellectual impairment
Chromosomal abnormalities:
Mutation on chromosome #4
Achondroplasia
Lack of bone growth, primarily
affecting limbs, skull, and
vertebrae
Muscular weakness
Usually no abnormalities of
other organs
No cognitive or intellectual
impairment
Chromosomal abnormalities:
Mutation on X chromosome
Duchenne Muscular Dystrophy
Abnormal growth in all muscles
leading to severe weakness
Usually no abnormalities of
other organs
No cognitive or intellectual
impairment
Respiratory failure often leads
to death in early adult years
Drugs taken by mother;
Cross placenta to embryo
Hundreds of drugs known
to cause birth defects.
Potential for birth defects = most common reason drugs
restricted
Best known = Thalidomide (sedative):
Limb abnormalities
Absent (whole or part),
Short, Malformed
Defects in heart, lungs,
digestive system
Similar abnormalities
occurred in children whose
mothers took the acne drug
Accutane (isotretinoin)
during pregnancy.
Examples of other drugs linked to birth defects:
Aminopterin
or
Methotrexate
(antitumor agents)
Defects of brain, nerves,
skeleton (often limbs)
eyes, heart
Diethylstilbesterol
( ↓ miscarriage)
Defects of uterus, vagina
Vitamin A
Defects of brain, spinal cord,
face (cleft palate/lip), heart
Streptomycin
(antibiotic)
Deafness from damage to
inner ear
Diseases and infections of mother may cause
birth defects, including many diseases which are
relatively mild to her
Bacteria, viruses, etc. may cross
placenta to embryo
or
Antibodies produced by mother's
immune system may cross placenta
and damage embryo
Some common diseases linked to birth defects
Cytomegalovirus: Defects of head &
face, brain, eyes,
other organs
Rubella:
Defects of eyes, brain,
heart; Deafness
Herpes simplex
virus:
Defects of eyes,
head, brain
Examples of chemicals in food, air, water linked to
birth defects when they cross the placenta to the embryo
Mercury:
Abnormalities of brain, nerves, heart
Abnormalities of skeleton (often limbs)
Blindness, deafness. spasticity
Intellectual impairment
Lead:
Abnormalities of brain, bone
Blindness, deafness
Intellectual impairment
Ethanol:
Decreased fetal growth
Abnormalities of face (cleft palate/lip)
Emotional & learning problems
Physical trauma to fetus can cause birth defects:
Increased uterine pressure can
cause dislocated hip, shoulder,
deformed limbs, deformed skull
Constriction by
umbilical cord can
cause amputation of
limbs
Damage to the brain
before or during birth can
lead to cerebral palsy
Again: Cause of birth defects is unknown more
than half the time