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   DIAGNOSING CADASIL   
      
   Magnetic Resonance Imaging (MRI)   
   Skin Biopsy   
   Genetic Testing   
      
   Magnetic Resonance Imaging (MRI)   
   Magnetic resonance imaging (MRI) is a method for making detailed images of the   
   brain. In CADASIL, the MRI shows changes in the deep regions of the brain,   
   particularly in the white matter. The white matter lies below the outer layers   
   of the brain (the    
   cortex or gray matter) and forms the connections among brain areas so that   
   they work in a unified way. The blood supply to the white matter is provided   
   by small blood vessels which make it especially vulnerable to CADASIL. Other   
   disorders, such as    
   multiple sclerosis, cause white matter changes that look similar on MRI, so   
   CADASIL cannot be diagnosed from MRI alone. However, CADASIL might be   
   suspected if the white matter changes are concentrated in certain brain areas   
   (frontal lobes and/or temporal    
   lobes).   
      
   MRI uses magnetic fields and radio waves to make its images and involves no   
   x-rays or other forms of radiation. It is a safe and reliable test method with   
   few health risks. However, it is not safe for people with pacemakers or   
   certain other implanted    
   medical devices or for people who may have small metal fragments or dust in   
   their eyes. It is often helpful to have MRI scans repeated every few years to   
   look for progression of the disease.   
      
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   Skin Biopsy   
   CADASIL causes characteristic changes in the blood vessels in almost all   
   regions of the body. These vascular changes may be crucial in making a   
   diagnosis but can only be seen under a powerful electron microscope. Since the   
   blood vessels of the brain    
   cannot be analyzed directly, microscopic examination is performed on the more   
   readily accessible blood vessels in the skin. Under local anesthesia, a small   
   piece of skin is taken from the upper arm or thigh and the resulting wound is   
   closed with one or    
   two sutures. The tissue sample is then sent to a facility that has an electron   
   microscope. Under magnification, the changes typical of CADASIL can be seen in   
   the vascular walls. One of these characteristics is called granular   
   osmiophilic material, or GOM,   
    which is thought to be made of clumps of excess protein. If such changes can   
   be detected, the CADASIL diagnosis can be regarded as confirmed. The key   
   limitation to skin biopsy is that there is a small chance that the disease   
   could be missed if the skin    
   specimen does not happen to contain any diseased blood vessels.   
      
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   Genetic Testing   
   CADASIL is caused by a mutation (mistake) in the structure of the NOTCH3 gene.   
   It turns out, however, that the mutation can take different forms, and that   
   not all people with CADASIL have the same precise mutation. Within a family,   
   all those affected    
   with the disease will have the same NOTCH3 mutation. Detection of a mutation   
   is considered 100% proof of the existence of the disease. Since the NOTCH3   
   gene is very large, the search for mutations can be tedious, complex, and   
   expensive. For this reason,    
   many diagnostic laboratories test only the locations on the gene most likely   
   to contain the CADASIL mutation. This makes the genetic test somewhat easier   
   and less expensive, but some mutations may be missed. Therefore, in individual   
   cases, it may be    
   necessary to search the entire gene for a mutation.   
      
   Only a small amount of blood, which can be taken from a vein, is needed for   
   genetic testing. In the United States, there is only one commercial laboratory   
   that offers genetic testing for CADASIL. You and/or your physician can find   
   more detailed    
   information about the lab by visiting www.athenadiagnostics.com.   
      
   A decision to test for a genetic disorder is an important and sometimes   
   difficult one. Learning that you have a genetic disorder can be    
   sychologically distressing and can have an impact on health insurance. Some   
   people with symptoms may want to know -    
   others may not. The decision to have the test can be even more difficult for   
   healthy members of a CADASIL family. You should discuss your concerns with   
   your doctor before having the test. Genetic counselors have special expertise   
   in working with people    
   with genetic disorders and may provide helpful advice and guidance in making   
   your decisions.   
      
      
      
       
      
   Memory and Aging Program   
   Butler Hospital   
   345 Blackstone Blvd.   
   Providence, RI 02906   
      
   401-455-6403   
   Fax: 401-455-6405   
   memorydisorder.org   
      
      
   Website: Thea Brennan-Krohn   
   email: theabk@yahoo.com   
      
      
      
   http://www.butler.org/cadasilsite/aboutcadasil/diagnosing.htm   
      
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