rs137852641 — NOTCH3

NOTCH3 Arg332Cys — The Most Common Inherited Cause of Stroke

NOTCH3 encodes a cell-surface signalling receptor expressed almost exclusively in vascular smooth muscle cells. When NOTCH3 functions normally, it helps small arteries maintain their structure and tone throughout life. The Arg332Cys variant disrupts a cysteine in the sixth [epidermal growth factor-like (EGF-like) repeat | NOTCH3's extracellular domain is made of 34 EGF-like repeats, each stabilised by three disulfide bonds formed by six precisely-spaced cysteine residues. Odd-numbered cysteines in each repeat pair with even-numbered ones; adding or removing a cysteine breaks that pairing and causes the domain to misfold] of NOTCH3's extracellular domain — a change that, over decades, silently destroys the small arteries that supply deep brain structures. The resulting disease, [CADASIL | Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy — the name describes the anatomy: arteries (arteriopathy) supplying deep gray/white matter (subcortical) produce both small strokes (infarcts) and white matter damage (leukoencephalopathy)], is the most common inherited cause of stroke and vascular dementia in adults.

The Mechanism

NOTCH3's 34 EGF-like repeats depend on correctly paired disulfide bonds for structural integrity. Each repeat contains six cysteines that form three obligate pairs (C1-C2, C3-C4, C5-C6). The Arg332Cys substitution introduces an unpaired cysteine in repeat 6, breaking the rigid pairing rule. The [misfolded extracellular domain | The monomeric NOTCH3 ECD cannot be cleared by normal proteostasis and accumulates at the vessel wall surface. This aggregate forms the pathological hallmark of CADASIL: GOM (granular osmiophilic material) deposits visible on electron microscopy of skin or brain vessel biopsies] cannot fold correctly, and the protein accumulates on the surface of smooth muscle cells rather than participating in normal signalling.

Over years of accumulation, the [smooth muscle cells | The principal cellular target in CADASIL — smooth muscle cells in small penetrating arteries degenerate and are replaced by fibrosis, thickening the vessel wall and reducing the lumen. The result is chronic hypoperfusion and vulnerability to small infarcts in territory the arteries supply: deep white matter, basal ganglia, thalamus, brainstem] progressively degenerate and are replaced by fibrosis. The small penetrating arteries supplying deep brain structures — the lenticulostriate arteries, thalamic perforators, brainstem perforators — narrow and stiffen, eventually causing lacunar infarcts and the characteristic white matter hyperintensities visible on FLAIR MRI. Because NOTCH3 is expressed almost exclusively in smooth muscle cells (not endothelium or neurons), the pathology is pure vasculopathy: neurons die not from a primary genetic defect but from the vascular failure upstream.

The Arg332Cys variant is located in exon 6 — a [less common mutation site for CADASIL | The majority of CADASIL mutations cluster in exons 3-4 (EGF-like repeats 1-5). Exon 6 mutations are rarer and may carry slightly different phenotypic features, including a lower rate of anterior temporal lobe involvement and possible lower penetrance in some families], contrasting with the more common exon 3-4 hotspot. Regardless of the exact exon location, any cysteine-altering NOTCH3 mutation is classified as pathogenic by the diagnostic criterion [defined by Rutten et al. | 2014, Expert Rev Mol Diagn, PMID 24844136]: gain or loss of a cysteine residue in any of the 34 EGF-like repeats.

The Evidence

A landmark UK Biobank analysis of 200,632 participants by Cho et al.¹¹ landmark UK Biobank analysis of 200,632 participants by Cho et al.
J Neurol Neurosurg Psychiatry 2021 found cysteine-altering NOTCH3 variants in approximately 1 in 450 individuals in the general population — far more than the 1 in 15,000 estimated from classic CADASIL clinical case series, suggesting profound underdiagnosis. Carriers had a 2.33-fold increased stroke risk (p=0.0004), a 5-fold increased vascular dementia risk (p=0.007), significantly greater white matter hyperintensity volume, elevated lacune burden (5.97-fold increase), and increased cerebral microbleeds (4.38-fold increase) — the full neuroimaging signature of CADASIL, present in individuals who had never received a clinical diagnosis.

Phenotypic data specific to Arg332Cys comes from case series. Li et al. 2020²² Li et al. 2020
Annals of Translational Medicine characterized 12 published Arg332Cys cases with a mean symptom onset age of 37.8 ± 9.4 years, earlier than the 47-year average across all CADASIL mutations per GeneReviews. Stroke or TIA was the presenting event in 83.3%, cognitive decline in 58.3%, and psychiatric disturbance in 50%. Sano et al. 2011³³ Sano et al. 2011
Internal Medicine documented phenotypic heterogeneity even within families carrying identical Arg332Cys mutations: one proband presented with syncope only, another with recurrent ischemic events followed by intracranial hemorrhage — illustrating that clinical course is not precisely predictable from the genotype alone.

No proven disease-modifying therapy exists for CADASIL. Thrombolytic therapy and oral anticoagulants [probably increase intracerebral hemorrhage risk | GeneReviews CADASIL: cerebral microbleeds, present in 31-69% of CADASIL patients, represent fragile small vessels at high bleeding risk; anticoagulants that would normally benefit embolic stroke are counterproductive here] and are generally avoided. Antiplatelet therapy may reduce ischemic event risk and is widely used in practice, though randomized trial evidence is lacking. Blood pressure control is a clear priority: faster disease progression is documented in individuals with elevated systolic blood pressure.

Practical Actions

The central management goals for Arg332Cys carriers are: (1) secure a neurology referral and establish baseline MRI before symptoms appear, (2) control all modifiable vascular risk factors aggressively — especially blood pressure and smoking — because these accelerate an already progressive disease, (3) avoid iatrogenic hemorrhage from thrombolytics or anticoagulants in the acute stroke setting, and (4) enable cascade family testing so other carriers are identified before their first infarct.

Migraine with aura, present in 30-75% of CADASIL patients across mutations, is often the earliest symptom. Triptans have been used safely in CADASIL patients in published series without documented vascular complications, though the evidence base is observational. Standard migraine prophylaxis (beta-blockers, topiramate, valproate) follows general guidelines.

Pregnancy carries a modestly elevated risk of neurological events, particularly in the peripartum period. Maternal-fetal medicine consultation is recommended before conception. Antiplatelet therapy in pregnancy should be individualized with specialist input.

Interactions

No single-variant gene-gene compound action is specifically documented for rs137852641, but the broader CADASIL phenotype interacts strongly with modifiable vascular risk factors. Carriers who also have hypertension-amplifying variants (AGT, ACE), dyslipidaemia variants (APOE4, LDLR), or pro-inflammatory variants (IL-6, CRP) may have accelerated white matter lesion progression — though the interaction evidence is observational rather than established from controlled genetic studies.