Definition: Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.
Input: Context: Mutations in NOTCH3 are the cause of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a hereditary angiopathy causing stroke and vascular dementia. All CADASIL mutations identified so far result in the loss or gain of one cysteine residue within epidermal growth factor (EGF)-like repeat domains. Here an in-frame deletion causing a loss of three cysteine residues within EGF repeat 6 is reported. These data are consistent with the hypothesis that the change toward an odd number of cysteine residues within a given EGF repeat and therefore an unpaired, reactive cysteine residue is the common and critical molecular event in CADASIL.
Question: Which amino acid residue appears mutated in most of the cases reported with cadasil syndrome?
Output:
cysteine