The Spectrum of NOTCH3 Variants in an Australian CADASIL Cohort

<b>Background</b> Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an autosomal dominant neurological disorder caused by mutations in the <i>NOTCH3</i> gene. Disease-causing variants in <i>NOTCH3</i> are primarily missense variants altering the number of cysteine residues in the translated NOTCH3 protein. The genetic screening of the <i>NOTCH3</i> gene is currently considered the gold standard for CADASIL diagnosis. <b>Methods</b> The Genomics Research Centre has been performing diagnostic genetic testing for CADASIL since 1997. A total of 1281 patient samples suspected of having CADASIL were screened for <i>NOTCH3</i> mutations from January 1, 1997, to October 1, 2025. Genomic sequencing was performed using Sanger sequencing of selected <i>NOTCH3</i> exons or using next-generation sequencing to screen the entire <i>NOTCH3</i> gene. <b>Results</b> In total, 12.1% of patients had a cysteine-altering <i>NOTCH3</i> variant, including 49 variants in exons 2-24, and two variants in non-EGFr encoding exons. We also report the first CADASIL patient who is a compound heterozygote for two known pathogenic cysteine-altering <i>NOTCH3</i> variants, who presented with a severe early onset of stroke, migraine, and white matter changes. <b>Conclusions</b> The compound heterozygosity identified in this patient appears to be associated with an early onset of CADASIL symptoms. Our study contributes to the elucidation of the spectrum of <i>NOTCH3</i> variants associated with CADASIL. The majority of patients tested for CADASIL in this study did not contain a variant in <i>NOTCH3</i>, indicating that there are other genes or genetic variants contributing to disease in these patients.