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HUMAN REPRODUCTIONBIOLOGY 269
Previous sessions: discussed normal embryonic and fetal development.
Unfortunately, things don't always go right.
More than 150,000 children born each year with birth defects, or congenital malformations.
They are present in , and later become apparent in . Thus, they affect approximately
More than 4,000 different forms of birth defects known
Can affect any organ and Often affect multiple organs
They can be mild severe
Many possible causes:
However, cause is unknown ~ half the time
Chromosomal abnormalities:
Either:
Since all cells of all organs have same chromosomes, chromosomal abnormalities often affect many different organs
Incidences of chromosomal abnormalities in spontaneously aborted fetuses and live births
No. per 100 % surviving aborted to birth.... 3-4 sets of chromosomes 10 - 17 <0.01
Extra sex chromosome <1 >99Missing sex chromosome 10 < 1
Extra autosome 20 - 40 3Missing autosome 1 0
Damaged chromosome 2 - 3 35
Chromosomal abnormalities:
Already talked about
Can involve sex (X or Y) chromosomes or autosomal (other 44) chromosomes
Chromosomal abnormalities:
Trisomy 21, or Down's Syndrome~ 1 out of 660 live births
Abnormal face,Abnormal hands, feetHeart defectsDeafnessMarked mental retardation
Chromosomal abnormalities:
Turner's syndrome: X-~ 1 out of 500 live births
Short female; Poorly developed sexual characteristicsNever enters puberty therefore sterile.Defects in heart, lungs, vessels, bonesOccasionally mentally retarded
Chromosomal abnormalities:
Abnormality (missing piece) of chromosome #5Cri du chat syndrome
Abnormal crySmall head & faceEye abnormalitiesDamage to brainMarked mental retardation
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 = (sedative):
Limb abnormalities Absent (whole or part), Short, MalformedDefects in heart, lungs, digestive system
Thalidomide
Examples of other drugs linked to birth defects:
Aminopterin Defects of brain, nerves, or skeleton (often limbs) Methotrexate eyes, heart (antitumor agents)
Diethylstilbesterol Defects of uterus, vagina( ↓ miscarriage)
Vitamin A Defects of brain, spinal cord, face (cleft palate/lip), heart Streptomycin Deafness from damage to(antibiotic) inner ear
Defects of
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 orAntibodies produced by mother's immune system may cross placenta and damage embryo
Some common diseases linked to birth defects
Defects of head & face, brain, eyes, other organs
Defects of eyes, brain, heart Deafness
Defects of eyes, head, brain
Examples of chemicals in food, air, water linked to birth defects Cross placenta to embryo
Defects of brain, nerves, heart Defects of skeleton (often limbs) Blindness, deafness Spasticity Mental retardation
Defects of heart, brain Blindness, deafness
Decreased fetal growth Defects of face (cleft palate/lip) Emotional & learning problems
Methylmercury poisoningMinamata Japan, 1930s-1950s
Physical trauma to fetus can cause defects:
Dislocated hip, shoulder Deformed limbs Deformed skull
Amputation of limbs
Leg and foot deformities
Inadequate amniotic fluid and uterine pressure
Cord around neck
Again: Cause