Birth Defects

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Birth Defects

• By Amanda

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What causes birth defects?

• Genetic and environmental factors can cause birth
  defects. A single abnormal gene can cause birth
  defects.
• Every human has 20,000 to 25,000 genes that
  determine traits like eye and hair color. Each
  child gets half its genes from each parent. A
  person can inherit a genetic disease when one
  parent, who may or may not have the disease,
  passes along a single faulty gene, a dominant
  inheritance.
• Each child gets half its genes from each parent.
  A person can inherit a genetic disease when one
  parent (who may or may not have the disease)
  passes along a single faulty gene.
• This is called dominant inheritance. Many other
  genetic diseases are inherited only when both
  parents (who do not have those diseases) happen
  to carry the same abnormal gene and pass it on to
  a child. This is called a recessive inheritance.
  (continued on next slide)

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Examples of birth defects.

• Examples include achondroplasia (a form of
  dwarfism) and Marfan syndrome (a connective
  tissue disease).
• Examples include Tay-Sachs disease (a fatal
  disorder seen mainly in people of European Jewish
  heritage) and cystic fibrosis (a fatal disorder
  of lungs and other organs, affecting mainly
  Caucasians).
• There also is a form of inheritance (X-linked)
  where sons can inherit a genetic disease from a
  mother who carries the gene (usually with no
  effect on her own health). Examples include
  hemophilia (a blood-clotting disorder) and
  Duchenne muscular dystrophy (progressive muscle
  weakness).

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More examples

• Abnormalities in the number or structure of
  chromosomes can cause numerous birth defects. Due
  to an error that occurred when an egg or sperm
  cell was developing, a baby can be born with too
  many or too few chromosomes, or with one or more
  chromosomes that are broken or rearranged.
• Down syndrome, in which a baby is born with an
  extra chromosome 21, is one of the most common
  chromosomal abnormalities. Affected children have
  varying degrees of mental retardation,
  characteristic facial features and, often, heart
  defects and other problems.
• Babies born with extra copies of chromosome 18 or
  13 have multiple birth defects and usually die in
  the first months of life.
• Missing or extra sex chromosomes (X and Y) affect
  sexual development and may cause infertility,
  growth abnormalities, and behavioral and learning
  problems.

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What form do they take?

• Defects of limbs, heart and spinal cord represent
  about half of all abnormalities.
• The most common kinds of defect are those
  affecting the limbs (arms and legs). These
  include missing or extra fingers or toes,
  deficiencies in limb length, and abnormalities in
  positioning, such as club foot.
• Heart abnormalities represent the next most
  common category of defect. Common heart defects
  include 'holes in the heart' where blood can pass
  from one side of the heart to the other. Again,
  these may not all be detected at birth. The
  third most common kind of defect affects the
  spinal cord, such as spina bifida.
• Other defects commonly observed include those
  affecting the face (such as cleft lip and
  palate), problems with the development of the
  intestines and stomach, and problems affecting
  the sexual organs.Major chromosomal problems
  such as Down's syndrome (Trisomy 21) are found in
  about 0.15 per cent of births (about three babies
  in every 2000).

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What are the main environmental factors causing
birth defects?

• Thalidomide is perhaps the most notorious example
  of a drug that caused defects.
• It was brought on to the market after inadequate
  testing and specifically prescribed for pregnant
  women. Following this, much stricter rules about
  drug testing were introduced, and international
  monitoring programmes were put in place.
• Moderate alcohol use in pregnancy is a
  particularly tricky problem. Many women who abuse
  alcohol may also have unhealthy lifestyles -
  inadequate diet, smoking and lack of exercise,
  and this confuses the issue in establishing the
  exact role of alcohol.
• Smoking is bad for the development of the baby in
  a number of ways.
• Environmental causes (including exposure to
  drugs, radiation and illnesses) can be identified
  in about 10 per cent of birth defects. The risk
  of exposure to such environmental factors often
  causes great concern, although genetic causes are
  more common.
  (Continued on next slide)

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Other factors

• The exact causes of the remaining 65 per cent of
  defects are currently unclear. Many of these
  defects arise from an interplay of genetic and
  environmental factors. For instance, some babies
  may have a genetic susceptibility to certain
  environmental factors.
• If exposed to such factors during development,
  they may develop an abnormality. If they are not
  exposed to the factor, they will be perfectly
  normal.
• Another baby exposed to the same environmental
  factor, but who doesn't have the genetic
  susceptibility, may be entirely normal. This can
  make it difficult to pin down the exact cause of
  a defect.

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Statistics.

• Every 8 seconds a baby is born in the United
  States. Every hour 3 babies die.
• African American infants are more than twice as
  likely to die before their first birthday as
  white infants.
• Birth defects are the leading cause of infant
  mortality.
• One in five infant deaths is due to birth
  defects.
• Every 3 minutes a baby is born with a birth
  defect.
• Every 2 minutes a low birth weight baby is born.
• Every year nearly 3,900 babies are born weighing
  less than 1 pound at birth.
• Every minute a baby is born to a teen mother.
• Each day 406 babies are born to mothers who
  received late or no prenatal care.
• More than 1 in 10 infants is born premature.
• The US infant mortality rate is worse than 24
  other nations.

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What exactly is a birth defect?

• A birth defect is a problem that happens
  while the baby is developing in the mother's
  body. Most birth defects happen during the first
  three months of pregnancy.
• A birth defect may affect how the body looks,
  works or both.
• It can be found before birth, at birth or anytime
  after birth. Most defects are found within the
  first year of life.
• Some birth defects (such as cleft lip or
  clubfoot) are easy to see, but others (such as
  heart defects or hearing loss) are found using
  special tests (such as X-rays, CAT scans or
  hearing tests). Birth defects can vary from mild
  to severe.
• Some birth defects can cause the baby to die.
  Babies with birth defects may need surgery or
  other medical treatments, but, if they receive
  the help they need, these babies often lead full
  lives.

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What are the most common among birth defects?

• One of every 33 babies is born with a birth
  defect. A birth defect can affect almost any part
  of the body. The well-being of the child depends
  mostly on which organ or body part is involved
  and how much it is affected.
• Many birth defects affect the heart. About 1 in
  every 100 to 200 babies is born with a heart
  defect.
• Heart defects make up about one-third to
  one-fourth of all birth defects. Some of these
  heart defects can be serious, and a few are very
  severe.
• In some places of the world, heart defects cause
  half of all deaths from birth defects in children
  less than one year of age.
• Other common birth defects are neural tube
  defects, which are defects of the spine (spina
  bifida) and brain (anencephaly).
• They affect about 1 of 1,000 pregnancies. These
  defects can be serious and are often life
  threatening. They happen less often than heart
  defects, but they cause many fetal and infant
  deaths.

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More common effects.

• Birth defects of the lip and roof of the mouth
  are also common. These birth defects, known as
  orofacial clefts, include cleft lip, cleft palate
  and combined cleft lip and cleft palate.
• Cleft lip is more common than cleft palate. In
  many places of the world, orofacial clefts affect
  about 1 in 700 to 1,000 babies.
• These are only some of the most common birth
  defects. Two final points are worth noting.
  First, genetic conditions, though not mentioned
  so far, also occur often. Down's syndrome, for
  example, is a genetic condition that affects
  about 1 in 800 babies, but it affects many more
  babies who are born to older women.
• Second, a woman who is pregnant may miscarry a
  baby early, before it is time for the baby to be
  born. This often happens when the fetus has a
  severe birth defect.

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All of the most common birth defects.

• AnencephalyA fatal birth defect that happens
  when the neural tube does not fully close at the
  top. As a result, the skull and brain do not form
  properly. Babies with anencephaly die before or
  shortly after birth.EncephaloceleA birth defect
  that is often fatal. Part of a baby's skull does
  not form properly, and part of the brain is
  outside of the skull. Those babies who do survive
  often have severe physical and mental
  handicaps.Neural tubeThe tube along the back of
  an embryo which later becomes the spinal cord and
  brain.Neural tube defect (NTD)Problems in the
  growth of the spinal cord and brain in an embryo,
  when the neural tube doesn't close at the top
  (anencephaly) or the bottom (spina bifida). The
  defects occur in the first month of pregnancy,
  before most women know they are pregnant. About
  seven babies are born in the U.S. each day with
  these birth defects.Spina bifidaA birth defect
  of the backbone and spinal cord that leaves the
  spinal cord exposed. A person with spina bifida
  may have learning disabilities or problems going
  to the bathroom because of lack of bowel and
  bladder control, and usually needs crutches or a
  wheelchair to get around. Eighty to ninety
  percent of babies with spina bifida survive, and
  most lead productive lives.

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Pictures.

• anencephaly Tay-Sachs
• Achondroplasia
• Marfan syndrome