# The Spectrum of NOTCH3 Variants in an Australian CADASIL Cohort

## TL;DR

This study analyzed NOTCH3 gene variants in an Australian CADASIL cohort, finding 12.1% had disease-causing mutations and identifying a rare case of compound heterozygosity linked to early-onset symptoms.

## Contribution

The study reports the first CADASIL patient with compound heterozygosity for two pathogenic NOTCH3 variants and highlights the need to consider other genes for unexplained cases.

## Key findings

- 12.1% of patients had cysteine-altering NOTCH3 variants, including 49 in exons 2-24 and two in non-EGFr exons.
- A compound heterozygous patient showed severe early-onset CADASIL symptoms, suggesting a more aggressive disease course.
- Most patients without NOTCH3 variants suggest other genetic factors may contribute to CADASIL.

## Abstract

Background Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an autosomal dominant neurological disorder caused by mutations in the NOTCH3 gene. Disease-causing variants in NOTCH3 are primarily missense variants altering the number of cysteine residues in the translated NOTCH3 protein. The genetic screening of the NOTCH3 gene is currently considered the gold standard for CADASIL diagnosis. Methods 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 NOTCH3 mutations from January 1, 1997, to October 1, 2025. Genomic sequencing was performed using Sanger sequencing of selected NOTCH3 exons or using next-generation sequencing to screen the entire NOTCH3 gene. Results In total, 12.1% of patients had a cysteine-altering NOTCH3 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 NOTCH3 variants, who presented with a severe early onset of stroke, migraine, and white matter changes. Conclusions 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 NOTCH3 variants associated with CADASIL. The majority of patients tested for CADASIL in this study did not contain a variant in NOTCH3, indicating that there are other genes or genetic variants contributing to disease in these patients.