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:
Short stature after birth
Webbing of Neck
Caved in Chest Bones
In boys, Testes that do not descend into the scrotum.
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:
Drooping of eyelids.
Downwards slanting eyes with arched eyebrows
Extra skin fold at the inner angle of the eyes.
Increased distance between the eyes.
Very Blue or blue green eyes
Flat broad root of the nose.
Short broad neck with skin folds
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
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.
On an average, puberty is delayed by about two years in both sexes.
During the first years of life the children may have great feeding and nutrition problems and frequent respiratory tract infections.
Only a few children with Noonan syndrome are seriously handicapped. Delayed motor development and speech may be seen in about 25% of the children.
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 %
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.
A mild type of hearing impairment has been reported.
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.
Repeated attacks of epilepsy have been described in a few cases
Reduced fertility in men. Women’s fertility is normal.