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Noonan Syndrome
Synonynms
Jacqueline Noonan,
paediatrician and heart specialist in 1963, published a report on a
small group of patients with typical facies, congenital heart defect,
and some clinical features similar to Turner syndrome, but with normal
chromosomes. Its after her that this syndrome has been named.
Noonan syndrome is inherited as an autosomal
dominant condition. This means that the Noonan gene is on a non-sex
(autosomal) chromosome and is transmitted from parent with a 50%
probability to child. Although one dose of the Noonan gene is enough to
cause the syndrome. A gene for Noonan syndrome (NS1) has been mapped to
chromosome number 12. There are several different Noonan genes.
The frequency of the Noonan syndrome is
estimated to be between 1:1,000 and 1:2,500 in the general population
Main features of this syndrome are:
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Pulmonary
Stenosis |
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Short
stature after birth |
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Webbing
of Neck |
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Caved
in Chest Bones |
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In
boys, Testes that do not descend into the scrotum.
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Other possible heart defects are hypertrophic
cardiomyopathy (thickened heart muscle), atrial septum defect
(hole in the wall separating the anterior heart chambers), ventricular
septum defect (hole in the wall separating the main heart chambers),
septal hypertrophy or a combination of all these defects.
Other Facial features that may be present
in this syndrome are -
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Drooping
of eyelids. |
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Downwards
slanting eyes with arched eyebrows |
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Extra skin
fold at the inner angle of the eyes. |
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Increased
distance between the eyes. |
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Broad
forehead |
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Very Blue
or blue green eyes |
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Curly hair |
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Flat broad
root of the nose. |
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Short
broad neck with skin folds |
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Many
pigmented birth marks |
Variations occur in the facial features
and they change with the age. As the child grows, the face gradually
becomes more normal, often more triangular with a high forehead.
Other features of this syndrome
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The birth
length and weight of children with Noonan syndrome are often
normal. The increase in height in both boys and girls is less than
normal throughout the whole growing period. |
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On an
average, puberty is delayed by about two years in both sexes. |
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During the
first years of life the children may have great feeding and
nutrition problems and frequent respiratory tract infections. |
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Only a few
children with Noonan syndrome are seriously handicapped. Delayed
motor development and speech may be seen in about 25% of the
children. |
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Studies
have shown that these children’s IQ was within normal limits,
though in most cases in the lower range of normal. Mental
retardation in approx. 35 % |
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Many of
those with Noonan syndrome have a form of visual disturbance,
squinting, near sight, or long sight, which may necessitate use of
spectacles. The visual disturbance is usually mild. |
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A mild
type of hearing impairment has been reported. |
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Children
with Noonan syndrome often have dental problems. 1/3 of them have
wrongly positioned teeth. The teeth often appear late and in an
abnormal order. |
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Repeated
attacks of epilepsy have been described in a few cases |
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Reduced
fertility in men. Women’s fertility is normal. |
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