The Role of Genetics
It is estimated that between 7% and 20% of aneurysms occur in individuals with a family history of same. The Familial Intracranial Aneurysm study screened first degree relatives of those affected by brain aneurysms and who were over the age of 30 years, smoked or had a history of hypertension. 19% were found to harbour an asymptomatic cerebral aneurysm. It is not known wheter that prevalence would have been less if those screened had not smoked or had their hypertension treated but it seems likely. Similar studies have suggested that aneurysms occurring in patient-siblings have a higer risk of rupture than those without such an assosciation. The absolute numbers of people so identified however are so small as to reduce cofidence in the strength of that assertion.
A large numbe of gene variants have been assosciated with the development and rupture of aneurysms without predominant molecular markers for risk of rupture being identified. It is believed that a susceptiblity gene could operate by coding for abnoral vessel wall tissues or by increasing the suscpetibility of an individual to envoromental stresses on the vessel wall for e.g. cigarette tar. It is likely that a gene capapble of producing the disease would likely be recieved from one parent only (autosomal dominant inheritence)
Screening for Cerebral Aneurysms
There is currently a great deal of confusing advice available about whether patients should be screened for cerebral aneurysms that have not caused symptoms. This reflects a good deal of uncertainty in the medical profession as to whether such screening actually protects patients from harm. There remains concern that seeking out asymptomatic aneurysms may unnecessarily expose patients to risks from treatment or to anxiety about a condition which would not be otherwise affecting them.
If you are considering screening we recommend speaking to a specialist with experience of treating cerebral aneurysms before undergoing any imaging tests. At present in the UK is reccomended only for those individuals who have two or more first-degree relatives (parent, sibling or child) affected by aneurysm.
Given the well documented risks of death or disability resulting from aneurysm rupture it is superficially attractive to secure them before they can cause harm. However the following need to be borne in mind:
- Not every aneurysm will go on to rupture
- The treatment of an unruptured aneurysm carries risks to life and independence of its own
- The risk of treating aneurysm may so outweigh the short term benfit that conservative treatment is recommended
- A negative MR or CT scan today is not a guarantee that an aneurysm could not develop in the future.
There is little good quality scientific data to guide us as to which patients might benefit from screening. In the future it is hoped that a better understanding of individualised risk will come from understanding:
- the individual's genetic make-up
- their enviromental risk factors (e.g. smoking) individuals are exposed to
- the individual stresses acting on each aneurysm wall determined with specialised imaging
Should Children be Screened for Aneurysms?
Cerebal aneurysms do occur inpersons under the age of 18 years but account for only 5% of all cerebral aneurysm coming to medical attentions. Cases occurring in children are ore frequently assosciated with an inherent genetic risk to develop aneurysms. Rather than screening siblings therefore in a case of a paediatric aneurysm it may first be preferable to first attempt to establish a clinical diagnosis for the index patient by referral to a clinical geneticist. it is not recommended to screen the asymptomatic children of adult patients with cerebral aneurysms who do not have two or more affected first-degree relatives.