DEFINITION
Spina bifida (Latin: "split
spine") is a developmental birth defect involving
the neural tube: incomplete closure of the embryonic
neural tube results in an incompletely formed spinal
cord. In addition, the vertebrae overlying the open
portion of the spinal cord do not fully form and remain
unfused and open. This allows the abnormal portion
of the spinal cord to protrude through the opening
in the bones. There may or may not be a fluid filled
sac surrounding the open spinal cord. Other neural
tube defects include anencephaly, a condition in which
the portion of the neural tube which will become the
cerebrum does not close, and encephalocele, which
results when other parts of the brain remain unfused.
Spina bifida malformations fall into three categories:
spina bifida occulta, spina bifida cystica (myelomeningocele),
and meningocele. The most common location of the malformations
is the lumbar and sacral areas of the spinal cord.
Myelomeningocele is the most significant form and
is that which leads to disability in most affected
individuals. The terms spina bifida and myelomeningocele
are usually used interchangeably.
Spina bifida can be surgically closed after birth,
but this does not restore normal function to the affected
part of the spinal cord and an individual with this
condition will have dysfunction of the spinal cord
and associated nerves from the point of the open defect
and below. Intrauterine surgery for spina bifida has
also been performed and the safety and efficacy of
this procedure is currently being investigated. The
incidence of spina bifida can be decreased up to 70
percent when daily folic acid supplements are taken
prior to conception.
SYMPTOMS
Spina bifida is caused by the failure of the neural
tube to close during the first month of embryonic
development (often before the mother knows she is
pregnant).
Normally the closure of the neural tube occurs around
28 days after fertilization.[3] However, if something
interferes and the tube fails to close properly, a
neural tube defect will occur. Medications such as
some anticonvulsants, diabetes, having a relative
with spina bifida, obesity, and an increased body
temperature from fever or external sources such as
hot tubs and electric blankets can increase the chances
a woman will conceive a baby with a spina bifida.
However, most women who give birth to babies with
spina bifida have none of these risk factors, and
so in spite of much research, it is still unknown
what causes the majority of cases.
The varying prevalence of spina bifida in different
human populations and extensive evidence from mouse
strains with spina bifida suggests a genetic basis
for the condition. As with other human diseases such
as cancer, hypertension and atherosclerosis (coronary
artery disease), spina bifida likely results from
the interaction of multiple genes and environmental
factors.
Treatments
Research has shown that lack of folic acid (folate)
is a contributing factor in the pathogenesis of neural
tube defects, including spina bifida. Supplementation
of the mother's diet with folate can reduce the incidence
of neural tube defects by about 70 percent, and can
also decrease the severity of these defects when they
occur. As yet it is unknown how or why folic acid
has this effect.
Spina bifida does not follow direct patterns of heredity
like muscular dystrophy or haemophilia. Studies show
that a woman who has had one child with a neural tube
defects such as spina bifida, has about a three percent
risk of having another child with a neural tube defect.
This risk can be reduced to about one percent if the
woman takes high doses (4 mg/day) of folic acid before
and during pregnancy. For the general population,
low-dose folic acid supplements are advised (0.4 mg/day).
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