From Asymptomatic Carriers To Cadasil: Context-Dependent Phenotypic Variability Of The Notch3 P.Arg1231Cys Variant Across Three European Cohorts And Potential Implications Of Ldl Cholesterol

Background: CADASIL caused by cysteine-altering NOTCH3 variants, the most frequent hereditary cerebral small vessel disease worldwide, is characterized by marked phenotypic variability. Mutation location within the EGFr domains of the NOTCH3 receptor has emerged as a key determinant of this variability. We investigated phenotypic variability and potential modifiers of CADASIL expression by comparing individuals harbouring the same pathogenic NOTCH3 variant across distinct recruitment settings in three European countries. Methods: We compared clinical features, MRI markers, and cardiovascular risk factors among individuals harbouring the p.Arg1231Cys NOTCH3 mutation across three distinct recruitment settings: a multigenerational founder population from Cilento, Italy (CILCAD), a population-based cohort from the UK Biobank (UKB), and a clinically referred cohort from a national referral centre in Lariboisiere Hospital, Paris, France (LRB). In addition, CILCAD carriers were compared with NON-Carriers from the same population. The NOTCH3 locus was finally analysed to define the shared haplotype in CILCAD and explore potential genetic contributions to phenotypic variability. Findings: By comparing populations from three European countries, this study showed marked context-dependent phenotypic variability associated with the sole pathogenic p.Arg1231Cys NOTCH3 variant. In CILCAD, a multigenerational founder population, the haplotype carrying the NOTCH3 mutation also predisposes to decreased LDL levels, resulting in an unusually low LDL cholesterol profile in this sample. Strikingly, these very low LDL levels were associated with a higher likelihood of stroke. Interpretation: In European carriers of NOTCH3 p.Arg1231Cys, factors beyond mutation location, including genetic background, may substantially shape disease expression, while exceptionally low LDL levels could paradoxically be associated with greater disease severity.