The Genetics
Treacher Collins Syndrome (TCS) is Autosomal Dominant. Autosomal means
that males and females are equally affected. In dominant
inheritance the chance of passing on the disorder is 50%. If the
gene is inherited it will result in an affected individual.
The features of TCS are, however, variable so that whilst some people may
be severely affected others can be so mildly affected that it is
very difficult to say whether they have the condition or not.
All human genetic information is carried on structures called
chromosomes, of which there are 46 in most cells of the body. Of
these 46 chromosomes, two are involved in determining the baby's
sex whilst the remainder are made up of 22 pairs.
Each chromosome contains many genes, each one having the ability to
produce a certain characteristic. Under normal circumstances each
of a pair of chromosomes looks alike and at the same position on
each chromosome are genes determining the same characteristic.
Usually these genes are identical although in some cases (for instance in
TCS) one gene is different from its opposite number and cannot
produce its normal characteristic - the genetic information is
effectively broken.
If either parent has TCS there is a 50-50 chance that each of their
children may be affected. If the TCS (broken) gene is passed from
parent to child the child will be affected. In approximately 60%
of cases, however, there is no previous family history of the
condition - neither parent has it. In this case the child has
developed TCS as a result of genetic mutation, not through
hereditary causes.
Although the broken gene has now been found there is still a great deal
of research to be done to gain a much better understanding of the
mechanisms underlying TCS. Moreover, this may also lead to a
better idea of the mechanisms responsible for other forms of
conductive deafness. Identification of the gene should also
ultimately aid early diagnosis of TCS, which will be particularly
useful for those people with very mild TCS and in whom clinical
diagnosis is correspondingly difficult.
As a result of the earlier discovery of the chromosome upon which the
gene responsible for causing TCS lies upon it is now possible to
predict who is and who is not affected by TCS with a very high
degree of accuracy (greater than 95%). Unfortunately a test such
as this will not be applicable to all families until a later point
in the ongoing research. The families that would be potentially
suitable for testing are those families in which there is a
clearly defined history of TCS and not those where TCS has arisen
without a previous family history.
At present there is no reliable prenatal testing for TCS. Specialist
ultrasound can sometimes give an indication that a baby may be
affected but cannot indicate the severity.
X-rays can sometimes help to determine whether a person has TCS.
Any genetic testing/consultation should be carried out by specially
qualified geneticists who have experience of TCS.
For more information about the TCS research project contact:
Prof. Michael Dixon
Department of Cell and Structural Biology
University of Manchester School of Biological Sciences
Stopford Building
Oxford Road
Manchester
M13 9PT
