Clinical and neuroradiological spectrum of biallelic variants in NOTCH3

Abstract

Background: NOTCH3 encodes a transmembrane receptor critical for vascular smooth muscle cell function. NOTCH3 variants are the leading cause of hereditary cerebral small vessel disease (SVD). While monoallelic cysteine-involving missense variants in NOTCH3 are well-studied in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), patients with biallelic variants in NOTCH3 are extremely rare and not well characterised.

Methods: In this study, we present clinical and genetic data from 25 patients with biallelic NOTCH3 variants and conduct a literature review of another 25 cases (50 patients in total). Brain magnetic resonance imaging (MRI) were analysed by expert neuroradiologists to better understand the phenotype associated with biallelic NOTCH3 variants.

Findings: Our systematic analyses verified distinct genotype-phenotype correlations for the two types of biallelic variants in NOTCH3. Biallelic loss-of-function variants (26 patients) lead to a neurodevelopmental disorder characterised by spasticity, childhood-onset stroke, and periatrial white matter volume loss resembling periventricular leukomalacia. Conversely, patients with biallelic cysteine-involving missense variants (24 patients) fall within CADASIL spectrum phenotype with early adulthood onset stroke, dementia, and deep white matter lesions without significant volume loss. White matter lesion volume is comparable between patients with biallelic cysteine-involving missense variants and individuals with CADASIL. Notably, monoallelic carriers of loss-of-function variants are predominantly asymptomatic, with only a few cases reporting nonspecific headaches.

Interpretation: We propose a NOTCH3-SVD classification depending on dosage and variant type. This study not only expands our knowledge of biallelic NOTCH3 variants but also provides valuable insight into the underlying mechanisms of the disease, contributing to a more comprehensive understanding of NOTCH3-related SVD.

Funding: The Wellcome Trust, the MRC.

Keywords: CADASIL; Leukoencephalopathy; NOTCH3; Neurodevelopmental disorders; Stroke.

Fig. 1

Pedigrees of the families in the current study.

Fig. 2

Variants described in this study mapped to NOTCH3 exons and domains. The table provides details on identified variants, their effects, protein domains, and associated phenotypes. Prepared using cBioPortal (https://www.cbioportal.org/mutation_mapper). Green: EGFR domains. Yellow: LNR (Lin12 repeats), Purple and Orange: transmembrane domain, Pink: ANK domain, Red: PEST (proline, glutamic acid, serine, threonine rich) domain.

Fig. 3

Clinical characteristics of patients with biallelicloss-of-functionand cysteine-involving missense variants. Graph illustrating the differential frequency of clinical and neuroimaging features among patients with biallelic loss-of-function (blue), biallelic p. Arg1231Cys (grey), and other cysteine-involving missense mutations (orange).

Fig. 4

Neuroimaging features in biallelic NOTCH3-SVD. Axial FLAIR and T2-weighted imaging in patients with cysteine-involving missense (a-d, e-h) and loss-of-function (i-l, m-p) variants. Patient 39 exhibits extensive deep white matter involvement (b), affecting external capsules (open arrows, a), thalamus, and brainstem (c, d). Patient 38 shows fewer lesions, more prominent on the left hemisphere (f), involving temporal poles (open arrowheads, g), with mild basal ganglia, brainstem, and thalamic involvement (e, g, h). Patients 2 and 13 display pronounced white matter volume loss in posterior peritrigonal regions (squared-shape; arrowheads, i, m) with FLAIR signal intensity saturation (arrowhead, m), resembling periventricular leukomalacia. White matter lesions in both patients are predominantly periventricular, with linear perivascular extension (arrows, l, p). Brainstems are relatively spared in both patients (k, o).

Fig. 5

White matter hyperintensities volume comparison between patients with biallelic cysteine-involving missense variants (n = 5) and monoallelic CADASIL controls (n = 251). Graph shows that patients with biallelic variants (blue) did not exhibit larger white matter lesion volumes than patients with monoallelic CADASIL (red).

Fig. 6

Summary of NOTCH3-related disorders. Both monoallelic and biallelic missense mutations causing gain or loss of cysteine lead to CADASIL. Few cysteine-sparing missense variants have also been reported and linked to CADASIL. Biallelic loss-of-function variants are associated with severe phenotypes, including neurodevelopmental disorders, early leukoencephalopathy, and white matter volume loss. Monoallelic carriers of these variants remain asymptomatic. However, monoallelic truncating variants in the last exon, 33, downstream of the ANK domain, are thought to produce a truncated protein lacking the PEST domain and to cause increased NOTCH3 signalling; these variants are linked to lateral meningocele syndrome. Created using BioRender (https://app.biorender.com/). GOM: granular osmiophilic material.