The following is the letter we received from the Toronto Hospital for Sick Children, describing the DNA testing we were about to take.  Please note: the 50% chance for reoccurrence quoted below is only if you are part of the 2-6% that is herditary or already have 2 children with sagittal synostosis, which would be very rare.  A second child with sagitttal synostosis would be extremely unlikely to occur.

July 31 1998

It was a pleasure to meet with you and your children, Benjamin and Shauna, in the Genetics Clinic on July 20, 1998.  As you know, Benjamin and Shauna were referred by Dr. Humphreys for a genetic assessment because they were both born with sagittal craniosynostosis.  This letter will summarize the main points of our discussion.

Craniosysnostosis is defined as the premature joining of the bones in the skull.   Usually, the bones of a child's skull remain loosely connected to one another and gradually grow together to form the adult skull.  The growing brain exerts pressure on the skull and ultimately determines the final head shape.  If a suture fuses prematurely, growth will occur along the path of least resistance, that being the sutures that are still open.  This pressure forces the adjoining bones of the skull to grow abnormally leading to a characteristic head shape.  Early surgery, such as Benjamin and Shauna had, helps to remodel the bones of the skull and lead to a more typical skull shape.

Sagittal craniosysnostosis is estimated to occur in 1 in 4000 to 1 in 8500 live births and is the most common type of single suture craniosynostosis.  The majority of cases are sporatice; however, familial cases obviously do occur.  A review of the literature indicates that familial sagittal craniosysnostosis is seen with a frequency of 2% to 6%.  On occasion, a child with craniosysnostosis can have an underlying genetic syndrome.  Ou assessment of Benjamin and Shauna revealed that they have non-syndromic craniosysnostosis.

You may recall from our discussion that humans have approximately 100,000 pairs of genes, one inherited from each parent.  These genes are the instructuions on how to build and maintain a human body.  The exact cause of sagittal synostosis remains unknown in the majority of cases, however; some individuals with this condition have been found to have a change (mutation) in the fibroblast growth factor receptor 3 gene (FGFR3).   The function of this gene is to produce a protein (a receptior on a cell) which receives signals for the development of bone and cartilage in the skull bones.  When one member of the FGFR3 gene pair is not working, the bones of the skull do not develop as they normally would, leading to craniosysnostosis.

During your appointment, we obtained a blood sample from Benjamin and Shauna for FGFR3 gene testing.  If a mutation is found in Benjamin and Shauna's FGFR3 genes, we would then offer to perform testing on the DNA we have stored on both of you.  It has been observed that a parent of children with craniosysnostosis can have an FGFR3 mutation and not exhibit any signs of craniosynostosis.  We would not test your DNA without forst obtaining your consent.  If a mutation is found in one of you, then your recurrence risk would be confirmed to be 50% and we would be able to offer you prenatal testing for sagittal synostosis in a future pregnancey.

If no mutation is found in Benjamin or Shauna's FGFR3 gene, the exact cause of their sagitaal sysnostosis would remain undetermined; however, based on there being two children in your family with this condition we would still quote you a recurrence risk of 50% for sagittal craniosysnostosis.  You would not be at increased risk for other types of non-syndromic or syndromic craniosysnostosis.

Although our understanding of the gentics of sagitaal synostosis is not complete, we can assure you that there is nothing that either of you did or did not do that causes your children to have craniosysnostosis.  We will be in touch with you when the result of the FGFR3 testing is available.  If you have any questions or concerns prior to then, please do nopt hesitate to contact us.

It was a pelasure meeting with both of you and your children.

Wishing you all the best.

Sincerely,

Shelley J. Kennedy, M.Sc; Genetics Counsellor

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