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Rett syndrome


Types and clinical signs

This is a developmental neurological syndrome that affects mainly females. It was first described in 1966. The main characteristic is regression of development with age. A girl affected with Rett syndrome develops normally or almost normally until the age of one year, at which time development stops and the child begins to regress in stages:
  • Initially there is a slowing of the rate of development that lasts a number of weeks or months, and then an obvious regression occurs. The girl loses her ability to speak between the ages of 1 and 4 years over a period of a few weeks. This period is eventful, and is accompanied by stereotypical arm movements reminiscent of hand washing, squeezing, bringing the hands together to the mouth, hand clapping, etc. Later, more slowly, there is regression in motor ability to the point of loss of ability to walk.

  • The head circumference is small at birth in these girls, and the rate of growth of the head slows down compared to their peers from the age of one year.

  • Some have epileptic episodes (Epilepsy - convulsions).

  • Their gait is unstable or wide-based, i.e. with a large distance between the feet, and they have rigid legs.

  • Sometimes there is lordosis or scoliosis of the trunk, and grinding of teeth.



Inheritance pattern

The disease is transmitted by X-linked inheritance and appears only in girls.

The gene for Rett syndrome is MECP-2, which is situated on the X chromosome.

Males with a mutation in this gene probably do not develop in the uterus, and are therefore not born.

In spite of this, isolated cases have been described of males with Rett syndrome.

In these males, the mutation in the gene is probably less severe than the mutation causing the condition in affected girls.

Most affected girls are born to healthy parents as a result of a new mutation. There are isolated cases in which the mutation was present in the mother but was not fully expressed so that she was able to reach adulthood without showing any signs of the disease. In these cases the abnormal gene is inherited by the daughter who does express it. These, however, are exceptional cases.

Penetrance

Almost always complete.

Associated features that can be demonstrated in tests performed during pregnancy

There are usually no defects. This condition cannot be diagnosed in pregnancy in a family in which there are no affected girls.

What is the risk of recurrence in a subsequent pregnancy?

Most affected girls are born to healthy parents as a result of a new mutation. As noted, there are isolated cases in which the mutation was present in the mother but was not fully expressed so that she was able to reach adulthood without manifesting any signs of the disease. The abnormal gene is inherited by the daughter who does express it. These are exceptional cases.

Molecular genetic information

The gene for the disease

Gene MECP-2.

Location

X chromosomes.

Genetic testing

Diagnostic testing

See information sheet: Finding the defect (mutation) by establishing the gene sequence - X-linked disease.

Carrier testing

There is usually no unaffected carrier status. After finding the defect in the affected girl, the mother can be tested for carrier status.

Fetal testing

As for diagnostic testing.
 
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