Strong clustering and stereotyped nature of Notch3 mutations in CADASIL patients

Background CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy) is commonly overlooked or misdiagnosed owing to its recent identification and its variable mode of presentation. The defective gene in CADASIL is Notch3, which encodes a large transmembrane receptor. To set up a diagnostic test and to delineate the NotchS domains involved in CADASIL, we undertook mutations analysis in this gene in a group of CADASIL patients. Methods 50 unrelated patients with CADASIL and 100 healthy controls were screened for mutations along the entire Notch3 sequence, by means of single-strand conformation polymorphism, heteroduplex, and sequence analysis. Findings Strongly stereotyped mis-sense mutations, located within the epidermal-growth-factor-like (EGF-like) repeats, in the extracellular domain of Notch3, were detected in 45 patients. Clustering of mutations within the two exons encoding the first five EGF-like repeats was observed (32 patients). All these mutations lead to loss or gain of a cysteine residue and therefore to an unpaired number of cysteine residues within a given EGF domain. None of these mutations was found in the 100 controls. Interpretation Because of the strong clustering and highly stereotyped nature of the pathogenetic mutations detected in CADASIL patients, an easy and reliable diagnostic test for CADASIL is feasible. The findings suggest that aberrant dimerisation of NotchS, due to abnormal disulphide bridging with another NotchS molecule or with another protein, may be involved in the pathogenesis of this disorder.