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Rubinstein Taybi syndrome

This results from a defect, usually the deletion of a small chromosomal segment, in the RTS gene, which is located on the short arm of chromosome 16. The deletion can extend to include the deletion of a number of additional genes next to the RTS gene. The greater the size of the deletion, the more severe will be the clinical presentation.

Clinical signs

This syndrome may involve a number of organs in the body, so that different patients have different clinical signs. The characteristic signs include:
  • Heart defects, mainly ventricular septal defect (VSD - a hole between the two ventricles of the heart) or atrial septal defect (ASD), etc.

  • Prominent wide thumbs with an outward deviation.

  • Characteristic facies - only experienced physicians are able to spot these changes because they are subtle and not marked. The nose is small with nostrils facing forwards, and the lips are thin.

  • The head circumference is relatively small and can deviate from the norm in the first few months of life.

  • All patients have delayed development and mental retardation of differing degrees of severity.

  • Some children may have additional defects such as in the development and structure of the kidneys and urinary tract, etc.

The diagnosis is usually made after examination by a clinical geneticist. Only in a relatively small number of cases can the defect be detected by the FISH test, using a specific fluorescent marker for the region of the RTS gene. In a regular chromosome test it is not possible to detect the specific deletion in Rubinstein Taybi syndrome. Amniocentesis chromosome testing is insufficient.

Inheritance pattern

Autosomal dominant.

Penetrance

Full

Associated problems that can be demonstrated by tests performed during pregnancy

Ultrasound examination can demonstrate a heart defect and other, less specific changes, such as kidney defects.

There are a few specialist ultrasound physicians who can examine the structure and posture of the thumb and attempt to decide whether these are characteristic for the syndrome - this can only be done in a family that has already had a child with this syndrome.

It must be remembered that the thumb sign cannot always be identified using the ultrasound transducer.

It can therefore not be anticipated that this condition can be identified in a family without children with this syndrome.

What is the risk of recurrence in a subsequent pregnancy?

Patients have a 50% risk in every pregnancy of transmitting the disease to their offspring, but this is usually irrelevant as patients generally never reproduce. Parents who have one child with Rubinstein Taybi syndrome have a small risk (less than 1%) of having another child with a similar problem, if they are healthy themselves. The same applies for other relatives such as siblings, uncles, etc.

Molecular genetic information

The gene for the disease

RTS.

Location

On the long arm of chromosome 16.

Genetic testing

Diagnostic test

FISH test using a specific fluorescent marker for the RTS gene can identify a very small proportion of cases. Attempts can be made to diagnose other cases by means of a molecular blood test in an overseas research laboratory coordinated through the genetic institute. The research laboratories that are studying this condition are attempting to characterize the deletion in the RTS gene. The methods differ, but the deletion can only be demonstrated in a small proportion of cases. In a regular chromosome test it is not possible to detect the deletion in Rubinstein Taybi syndrome. Amniocentesis chromosome testing is certainly insufficient for this purpose.

Carrier testing

Because the condition is transmitted as an autosomal dominant, every individual who carries the deletion is affected and there are no healthy carriers.

Fetal testing

As for diagnostic testing.
 
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