Background Collagen type IV alpha 1 (COL4A1) and alpha 2 (COL4A2) form heterotrimers critical for vascular basement membrane stability and function. Patients with COL4A1 or COL4A2 mutations suffer from diverse cerebrovascular diseases including cerebral microbleeds, porencephaly and fatal intracerebral hemorrhage (ICH). However, the pathogenic mechanisms remain unknown and there is a lack of effective treatment. Methods and Results Using Col4a1 and Col4a2 mutant mouse models, we investigated the genetic complexity and cellular mechanisms underlying the disease. We found that Col4a1 mutations cause abnormal vascular development, which triggers small vessel disease, recurrent hemorrhagic strokes and age-related macro-angiopathy. We showed that allelic heterogeneity, genetic context and environmental factors, such as acute exercise or anticoagulant medication, modulated disease severity and contributed to phenotypic heterogeneity. We found that intracellular accumulation of mutant collagen in vascular endothelial cells and pericytes was a key triggering factor of ICH. Finally, we showed that treatment of mutant mice with a FDA-approved chemical chaperone resulted in a decreased collagen intracellular accumulation and a significant reduction of ICH severity. Conclusions Our data are the first to show therapeutic prevention in vivo of ICH due to Col4a1 mutation, and imply that a mechanism-based therapy promoting protein folding might also prevent ICH in patients with COL4A1 and COL4A2 mutations.

Collagen, type IV, alpha 1 (COL4A1) and alpha 2 (COL4A2) form heterotrimers and are abundant components of basement membranes, including those of the cerebral vasculature. COL4A1 mutations are an increasingly recognized cause of multisystem disorders, including highly penetrant cerebrovascular disease and intracerebral hemorrhage (ICH). Because COL4A1 and COL4A2 are structurally and functionally associated, we hypothesized that variants in COL4A2 would also cause ICH. We sequence COL4A2 in 96 patients with ICH and identify three rare, nonsynonymous coding variants in four patients that are not present in a cohort of 144 ICH-free individuals. All three variants change evolutionarily conserved amino acids. Using a cellular assay, we show that these putative mutations cause intracellular accumulation of COL4A1 and COL4A2 at the expense of their secretion, which supports their pathogenecity. Furthermore, we show that Col4a2 mutant mice also have completely penetrant ICH and that mutations in mouse and human lead to retention of COL4A1 and COL4A2 within the endoplasmic reticulum (ER). Importantly, two of the three putative mutations found in patients trigger ER stress and activate the unfolded protein response. The identification of putative COL4A2 mutations that might contribute to ICH in human patients provides insight into the pathogenic mechanisms of this disease. Our data suggest that COL4A2 mutations impair COL4A1 and COL4A2 secretion and can also result in cytotoxicity. Finally, our findings suggest that, collectively, mutations in COL4A1 and COL4A2 contribute to sporadic cases of ICH.

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Achieving undetectable MRD (U-MRD) status after chemoimmunotherapy predicts longer progression-free and overall survival. The predictive factors and timing of relapse in patients with U-MRD and value of interim MRD analysis are ill-defined. This was a prospective study of 289 patients with CLL treated first-line with FCR. MRD analysis was performed after course 3 (C3) and at end-of-therapy (EOT) in bone marrow using 4-color flow cytometry (sensitivity 10−4). Eighteen percent of patients had U-MRD after C3 and 48% at EOT. U-MRD status at EOT was associated with longer PFS (median NR vs 38mo, p<0.001). MRD level (≤1% vs. >1%) after C3 predicted greater likelihood of U-MRD status at EOT (64% vs. 9%, p<0.001). PFS was significantly longer for patients with MRD ≤1% vs. >1% after C3 (median 73mo vs 41mo, p<0.001), but similar for <0.01% vs. 0.01–1%. Interim MRD status may therefore be used for risk stratification and to individualize therapy. Eighty-five patients with U-MRD status at EOT had yearly blood MRD monitoring; MRD re-emerged in 38/85, a median of 48mo after EOT and preceded clinical progression by a median of 24 months, which may allow development of early intervention strategies.

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