Clinical, MRI Features And Genetic Studies Of Suspected CADASILs From Mainland China

Background and purposeCerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary, adult-onset, cerebral vascular disease caused by a mutation in the NOTCH3gene, characterized by a non-arteriolosclerotic, non-amyloid diffuse microangiopathy. Its clinical features include recurrent lacunar strokes, migraine with aura, mood disorders, epilepsy and cognitive impairment progressing to dementia. The magnetic resonance imaging (MRI) features of CADASIL are diffuse, severe white-matter changes that frequent extend to the anterior pole of the temporal lobe and lacunar infarcts. The hallmark of CADASIL is the presence of deposits of granular osmiophilic material (GOM) in the small vessels. However, the sensitivity of electron microscopic evaluation of the skin arterioles for GOM is low (up to50%false negatives) and varies greatly from report to report. Furthermore, none of the known clinical or neuroimaging features is pathognomonic for CADASIL, and thus, genetic testing remains the gold standard for diagnosis.To date, more than190NOTCH3mutations have been characterized in more than500CADASIL families.The mutational spectrum of CADASIL includes missense point mutations, splice site mutations, and small in-frame deletions. The majority of mutations are missense point mutations (about95%). Clustering of mutations around exon2-6(almost90%) and especially exon4was reported and it was subsequently suggested that scanning should be limited to these exons for quick identification of suspected cases. However, studies have shown that the incidence and spectrum of the mutations that cause CADASIL vary among different populations. Even among Chinese patients of the same race, the spectrum of NOTCH3gene mutations is diverse. Hence, it is important to establish screening criteria that can reliably identify patients who require genetic testing. At present, the NOTCH3mutations located in exon2,3,4,6,10,11,18and20have been reported from China, while no obvious aggregation of NOTCH3mutational sites has been observed. The information about the incidence and spectrum of the mutations from mainland China is still limited.There are33exons in the NOTCH3gene and majority mutations demonstrated to date in CADASIL occur in exons2to23encoding the EGF-like repeats. The genetic analysis is costly and time-consuming because the NOTCH3gene is long and mutations can be found in any of the22exons codifying for the epidermal growth factors-like repeats, and it is therefore unsuitable for routine diagnosis. Hence, it would be important to have clinical and neuroimaging screening criteria to select with sufficient reliability the patients for genetic testing.The first aim of the present study was to make the definitive diagnosis by applying the NOTCH3gene screen among the patients with clinically suspected CADASIL from35Chinese families. The another aim of the present study was to compare the characteristics of patients diagnosed with CADASIL with those of patients who underwent NOTCH3gene exons2-23analysis and were found without pathogenic mutations. The study includes the following two parts: Part1NOTCH3gene mutation analysisObjective:To investigate the spectrum and incidence of NOTCH3mutations in mainland China patients with suspected CADASIL clinically.Methods:We performed NOTCH3gene analysis (exons2-23) in the probands from35families who were clinically suspected CADASILs.The corresponding exons were also analyzed in17family members from8independent families according to the result of the corresponding probands. The mutational rate and spectrum was analysis according to the test results and the reviewed literatures.Results:An initial screening of exons3and4in the35families identified7known mutations in11families and1novel mutation (p.C155W) in one family. Further screening of exons2,5-23in23families, another novel mutation (p.C43Y) was detected in one family. No causative mutation was detected in22families and100healthy controls. We also identified the p.R1175W variant which is of unknown significance and other two variants. The incidence of NOTCH3mutations in our group is37.1%(13/35). All the detected mutations in our series were located in exon2, exon 3and exon4.Conclusions:1. The p.C43Y in exon2and p.C155W in exon4both are novel mutations which have never been reported in other regions.2. The exon4and exon3of the NOTCH3gene were the mutational hotspot area in our series. The spectrum of NOTCH3mutations in our group was consistent with that reported in Caucasian, but different from that in Tanwai and Korea.3. The incidence of NOTCH3mutations in our group is37.1%.4. The p.R1175W variant detected in one family may be associated with the CADASIL in this family. Part2Clinical and MRI features of CADASIL patientsObjective:To report the characteristics of patients suspected to have cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) in whom NOTCH3gene pathogenic mutation was found. Methods:Comparison of clinical, familial, and neuroimaging features of patients with and without pathogenic mutations was performed. The clinical and neuroimaging features of CADASIL patients were demonstrated and the relationship between the cognition and MRI features was analyzed in the mutation group.Results:1. Clinical features:The onset age and the admit age were both earlier in CADASIL than in NOTCH3-negative patients:onset age (38.36±7.98vs49.05±8.41, p<0.001), admit age (45.52±9.61vs51.91±8.71, P=0.022); Some features were significantly more frequent in CADASIL than in NOTCH3-negative patients:positive family history (78.6%vs33.3%, p=0.015), hypertension prevalence rate (8.0%vs40.9%, p=0.014), and antihypertensive drug use (8.0%vs40.9%, p=0.014).2. MRI features:Some features were significantly more severe or frequent in CADASIL than in NOTCH3-nogative patients:severe leukoencephalopathy (70.81±44.90vs42.24±22.24, p=0.025), white matter changes extended to the anteriortemporal lobes (72.0%vs27.3%, p=0.003), external capsule involvement (84.0%vs27.3%, p<0.001), and numbers of lacunar infarcts (5.33±3.96vs2.00±2.45, p=0.007). The other features were balanced between the two groups. No feature was peculiar to either group. In CADASIL group, the MMSE scores have the negative correlation with leukoencephalopathy and numbers of lacunar infarcts, but no correlation with the micro bleeding.3. In CADASIL patients with abnormal MRA, the prevalence of hypercholesterolemia (62.5%vs17.6%, p=0.061) and hypertension prevalence rate (40.0%vs0.0%, p= 0.065) had a tendency to increase than CADASIL patients with normal MRA. But there was no difference in clincal and MRI features between the normal and abnormal MRA group.Conclusions:1. Severe leukoencephalopathy, white matter changes extended to the anteriortemporal lobes, external capsule involvement, numbers of lacunar infarcts, positive family history can be used as a clinical diagnosis of CADASIL specific indicator. The onset age less than45years may be advantage to CADASIL diagnosis. No other feature was peculiar to either group.2. Cerebrovascular disease risk factors and intracranial artery stenosis cannot be used as exclusive criteria of CADASIL.3. In CADASIL group, the MMSE scores have the negative correlation with leukoencephalopathy and numbers of lacunar infarcts, but no correlation with the micro bleeding.