* An MRI alone cannot confirm CADASIL.
* A spinal tap is not actually useful for diagnosis.
Genetic Test (blood test)
Only a small amount of blood, which can be taken from a vein, is needed for this genetic test. To be certain of a diagnosis, molecular screening is required. The gene implicated in the disease is the Notch3 gene located on the short arm of chromosome 19. It consists of 33 exons including 23 exons (from 2 to 24) which code for EFG-like patterns containing six cysteine residues. To date, all the mutations responsible for the disease have been located within these exons (2 to 24). They are very stereotyped and all of them lead to either the gain or loss of cysteine in one of the EGF-like patterns. The presence of this type of mutation confirms the diagnosis beyond all doubt.
CADASIL results in characteristic changes in the blood vessels. A very small skin biopsy is easily performed under local anesthetic. It is important this is processed in a special way allowing it to be looked at under high magnification using an electron microscope. Under this magnification, one can frequently see abnormal collections of material, which is called GOM (granular osmiophilic material). If these GOM are present, it can be almost certain that the individual does have CADASIL. However, the skin biopsy can be negative. The magnetic resonance scan (MRI) alone cannot confirm CADASIL, usually performed and shows characteristic appearances with abnormalities in the deeper parts of the brain or white matter, part-circularly in the temporal lobe poles. This can be repeated to determine whether the disease is progressing.