The Notch 3 gene is a big gene. It codes for a transmembrane protein (receptor) which has an intracellular and extracellular domain. The most common mutation in the gene is a missense mutation,seen in more than 90% of the cases. There are about 33 exons, which codes for extracellular domain. The extracellular domain contains 34repeats of EGFR. Each repeats contains 6 cysteine (Cys) residues. When mutation does occur, the number of cys residues either increases or decreases to an odd number. This mutation results in abnormal clearance of extracellular domain of notch 3 receptor.