Shifting the CARASIL Paradigm

HeterozygousHTRA1Mutations Cause Cerebral Small Vessel Diseases

Background and Objectives

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is a rare hereditary cerebrovascular disease caused by homozygous or compound heterozygous variations in the high-temperature requirement A serine peptidase 1 (HTRA1) gene. However, several studies in recent years have found that some heterozygousHTRA1mutations also cause cerebral small vessel disease (CSVD). The current study aims to report the novel genotypes, phenotypes, and histopathologic results of 3 pedigrees of CSVD with heterozygousHTRA1mutation.

Methods

Three pedigrees of familiar CSVD, including 11 symptomatic patients and 3 asymptomatic carriers, were enrolled. Whole-exome sequencing was conducted in the probands for identifying rare variants, which were then evaluated for pathogenicity according to the American College of Medical Genetics and Genomics guidelines. Sanger sequencing was performed for validation of mutations in the probands and other family members. The protease activity was assayed for the novel mutations. All the participants received detailed clinical and imaging examinations and the corresponding results were concluded. Hematoma evacuation was performed for an intracerebral hemorrhage patient with the p.Q318H mutation, and the postoperative pathology including hematoma and cerebral small vessels were examined.

Results

Three novel heterozygousHTRA1mutations (p.Q318H, p.V279M, and p.R274W) were detected in the 3 pedigrees. The protease activity was largely lost for all the mutations, confirming that they were loss-of-function mutations. The patients in each pedigree presented with typical clinical and imaging features of CVSD, and some of them displayed several new phenotypes including color blindness, hydrocephalus, and multiple arachnoid cysts. In addition, family 1 is the largest pedigree with heterozygousHTRA1mutation so far and includes homozygous twins, displaying some variation in clinical phenotypes. More importantly, pathologic study of a patient with p.Q318H mutation showed hyalinization, luminal stenosis, loss of smooth muscle cells, splitting of the internal elastic lamina, and intramural hemorrhage/dissection-like structures.

Discussion

These findings broaden the mutational and clinical spectrum of heterozygousHTRA1-related CSVD. Pathologic features were similar with the previous heterozygous and homozygous cases. Moreover, clinical heterogeneity was revealed within the largest single family, and the mechanisms of the phenotypic heterogenetic remain unclear. Overall, heterozygous HTRA1-related CSVD should not be simply taken as a mild type of CARASIL as previously considered.

Report of two pedigrees with heterozygous HTRA1 variants-related cerebral small vessel disease and literature review

BACKGROUND

Biallelic HTRA1 pathogenic variants are associated with autosomal recessive cerebral arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). Recent studies have indicated that heterozygous HTRA1 variants are related to autosomal dominant hereditary cerebral small vessel disease (CSVD). However, few studies have assessed heterozygous HTRA1 carriers or the genotype-phenotype correlation.

METHODS

The clinical data of two unrelated Chinese Han families with CSVD were collected. Panel sequencing was used to search for pathogenic genes, Sanger sequencing was used for verification, three-dimensional protein models were constructed, and pathogenicity was analyzed. Published HTRA1-related phenotypes included in PubMed up to September 2021 were extensively reviewed, and the patients' genetic and clinical characteristics were summarized.

RESULTS

We report a novel heterozygous variant c.920T>C p.L307P in the HTRA1, whose main clinical and neuroimaging phenotypes are stroke and gait disturbance. We report another patient with the previously reported pathogenic variant HTRA1 c.589C>T p.R197X characterized by early cognitive decline. A literature review indicated that compared with CARASIL, HTRA1-related autosomal dominant hereditary CSVD has a later onset age, milder clinical symptoms, fewer extraneurological symptoms, and slower progression, indicating a milder CARASIL phenotype. In addition, HTRA1 heterozygous variants were related to a higher proportion of vascular risk factors (p < .001) and male sex (p = .022).

CONCLUSION

These findings broaden the known mutational spectrum and possible clinical phenotype of HTRA1. Considering the semidominant characteristics of HTRA1-related phenotypes, we recommend that all members of HTRA1 variant families undergo genetic screening and clinical follow-up if carrying pathogenic variants.

Case Report: Diffuse Cerebral Microbleeds in Cerebral Autosomal Recessive Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is a hereditary cerebral small vascular disease caused by a homozygous mutation in the high-temperature requirement A serine peptidase 1 (HTRA1) gene. Cerebral microbleeds (CMBs) are increasingly being recognized as neuroimaging findings occurring with cerebrovascular disease and have different etiologies. Mild to moderate CMBs are not unusual in CARASIL, and they are observed to affect cortical and subcortical structures; in contrast, diffuse CMBs, especially in the cerebellum, are rare. In this case, we report a novel mutation of HTRA1 in a 43-year-old woman whose imaging indicated multiple CMBs in all lobes, brain stem, and cerebellum. The amount and location of CMBs vary in CARASIL cases, and the potential cause is not fully understood. This study revealed that specific imaging findings of this patient may be related to a new genetic mutation.

Relationships of Ischemic Stroke Occurrence and Outcome with Gene Variants Encoding Enzymes of Tryptophan Metabolism

Ischemic stroke is among the leading causes of mortality and long-term disability worldwide. Among stroke risk factors the importance of genetic background is gaining interest. There is a growing body of evidence of changes of metabolite levels and enzyme activities involved in the conversion of Trp during the course of cerebral ischemia. We compared the frequencies of ten SNPs of five genes related to Trp metabolism between groups of 122 ischemic stroke patients and 120 control individuals. Furthermore, we examined the mRNA levels of TPH1, IDO1 and KYAT1 genes in peripheral venous blood with the aim of assessing (i) whether there are changes in their expression during the course of stroke and (ii) does any of their investigated SNPs have an impact on gene expression. In seven cases out of ten studied polymorphisms we detected significant differences in frequencies in relation to ischemic stroke occurrence, etiology, and clinical parameters. We also detected changes in the expression of TPH1 and IDO1 genes during the course of the disease. We found that those IDO1 variants which show a trend towards elevated mRNA level are more frequent in stroke patients than in controls. Our results are important novel observations which suggest a causal relationship between elevated IDO1 expression and stroke etiology.

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL)

A 44-year-old Caucasian man presented with seizures and cognitive impairment. He had marked retinal drusen, and MR brain scan showed features of cerebral small vessel disease; he was diagnosed with a leukoencephalopathy of uncertain cause. He died at the age of 46 years and postmortem brain examination showed widespread small vessel changes described as a vasculopathy of unknown cause. Seven years postmortem, whole-genome sequencing identified a homozygous nonsense HTRA1 mutation (p.Arg302Ter), giving a retrospective diagnosis of cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy.

Genetically Confirmed CARASIL: Case Report with Novel HTRA1 Mutation and Literature Review

BACKGROUND

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is an extremely rare monogenic autosomal disease associated with the HtrA serine protease 1 (HTRA 1) gene mutation. Recently, a few genetically confirmed CARASIL cases with novel HTRA1 mutations have been reported in countries other than Japan.

CASE DESCRIPTION

Here, we report a case of a patient presenting with worsening right hemiplegia and hemiparesthesia. Physical examination revealed that the patient had typical clinical features of CARASIL including thinning hair, cognitive impairment, emotional changes, lumbago, and gait disorder. Brain magnetic resonance imaging showed abnormal diffuse symmetric changes in white matter and hypertensive diffusion-weighted imaging signals in the left centrum ovale and right splenium of the corpus callosum, and susceptibility-weighted imaging showed multiple cerebral microbleeds. Lumbar magnetic resonance imaging showed herniated disks with degenerative changes. A genetic test showed a novel homozygous nucleotide variation of c.847G>T in the HTRA1 gene, thereby resulting in p.Gly283Ter. Thus the patient met the diagnostic criteria for CARASIL. We provide a literature review of genetically confirmed CARASIL cases reported to date.

CONCLUSIONS

CARASIL is a rare autosomal recessive disease with an HTRA1 mutation. Familiarity with the early clinical and imaging features of CARASIL combined with a genetic test is key for its early diagnosis.

HTRA1-related autosomal dominant cerebral small vessel disease

BACKGROUND

Homozygous or compound heterozygous mutations in high temperature requirement serine peptidase A1 (HTRA1) gene are responsible for cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). Recently, increasing evidence has shown that heterozygous HTRA1 mutations are also associated with cerebral small vessel disease (CSVD) with an autosomal dominant pattern of inheritance. This study was aimed to analyze the genetic and clinical characteristics of HTRA1-related autosomal dominant CSVD.

METHODS

We presented three new Chinese cases of familial CSVD with heterozygous HTRA1 mutations and reviewed all clinical case reports and articles on HTRA1-related autosomal dominant CSVD included in PUBMED by the end of March 1, 2020. CARASIL probands with genetic diagnosis reported to date were also reviewed. The genetic and clinical characteristics of HTRA1-related autosomal dominant CSVD were summarized and analyzed by comparing with CARASIL.

RESULTS

Forty-four HTRA1-related autosomal dominant CSVD probands and 22 CARASIL probands were included. Compared with typical CARASIL, HTRA1-related autosomal dominant probands has a higher proportion of vascular risk factors (P < 0.001), a later onset age (P < 0.001), and a relatively slower clinical progression. Alopecia and spondylosis can be observed, but less than those in the typical CARASIL. Thirty-five heterozygous mutations in HTRA1 were reported, most of which were missense mutations. Amino acids located close to amino acids 250-300 were most frequently affected, followed by these located near 150∼200. While amino acids 250∼300 were also the most frequently affected region in CARASIL patients, fewer mutations precede the 200th amino acids were detected, especially in the Kazal-type serine protease domain.

CONCLUSIONS

HTRA1-related autosomal dominant CSVD is present as a mild phenotype of CARASIL. The trend of regional concentration of mutation sites may be related to the concentration of key sites in these regions which are responsible for pathogenesis of HTRA1-related autosomal dominant CSVD.

HTRA1-Related Cerebral Small Vessel Disease: A Review of the Literature

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is clinically characterized by early-onset dementia, stroke, spondylosis deformans, and alopecia. In CARASIL cases, brain magnetic resonance imaging reveals severe white matter hyperintensities (WMHs), lacunar infarctions, and microbleeds. CARASIL is caused by a homozygous mutation in high-temperature requirement A serine peptidase 1 (HTRA1). Recently, it was reported that several heterozygous mutations in HTRA1 also cause cerebral small vessel disease (CSVD). Although patients with heterozygous HTRA1-related CSVD (symptomatic carriers) are reported to have a milder form of CARASIL, little is known about the clinical and genetic differences between the two diseases. Given this gap in the literature, we collected clinical information on HTRA1-related CSVD from a review of the literature to help clarify the differences between symptomatic carriers and CARASIL and the features of both diseases. Forty-six symptomatic carriers and 28 patients with CARASIL were investigated. Twenty-eight mutations in symptomatic carriers and 22 mutations in CARASIL were identified. Missense mutations in symptomatic carriers are more frequently identified in the linker or loop 3 (L3)/loop D (LD) domains, which are critical sites in activating protease activity. The ages at onset of neurological symptoms/signs were significantly higher in symptomatic carriers than in CARASIL, and the frequency of characteristic extraneurological findings and confluent WMHs were significantly higher in CARASIL than in symptomatic carriers. As previously reported, heterozygous HTRA1-related CSVD has a milder clinical presentation of CARASIL. It seems that haploinsufficiency can cause CSVD among symptomatic carriers according to the several patients with heterozygous nonsense/frameshift mutations. However, the differing locations of mutations found in the two diseases indicate that distinct molecular mechanisms influence the development of CSVD in patients with HTRA1-related CSVD. These findings further support continued careful examination of the pathogenicity of mutations located outside the linker or LD/L3 domain in symptomatic carriers.

CARASIL with coronary artery disease and distinct cerebral microhemorrhage: A case report and literature review

Cerebral Autosomal Recessive Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CARASIL, Maeda syndrome) is an extremely rare autosomal-recessive genetic disorder with a serious arteriopathy causing subcortical infarcts and leukoencephalopathy. In less than 20 cases, a genetic mutation was proven. Patients suffer from alopecia, disc herniations, and spondylosis. Between the age of 30 and 40, the patients typically develop severe cerebral infarcts. Clinical symptoms, genetic study, magnetic resonance imaging (MRI), and coronary angiography of a patient with proven CARASIL are presented. The patient showed the typical phenotype with cerebral small-vessel disease, cerebral infarcts, spondylosis, and abnormal hair loss. Additionally, distinct cerebral microhemorrhage and a severe coronary artery disease (CAD) were found, which have not been reported before for CARASIL. Mutation screening revealed the presence of a homozygous c.1022G > T substitution in the HTRA1 gene. Evidence from other publications supports a pathogenetic link between the HTRA1 mutation and CAD as a new feature of CARASIL. This is the first report about CARASIL with a concomitant severe CAD. Thus, in patients with CARASIL, other vessel diseases should also be considered.

The association analysis between CYP24A1 genetic polymorphisms and the risk of ischemic stroke in Chinese Han population

AIMS

Stroke is a complicated neurological disease and the second leading cause of death in the world. We aimed to investigate the association between CYP24A1 genetic polymorphisms and ischemic stroke risk.

METHODS

In this case-control study, four single-nucleotide polymorphisms of CYP24A1 were selected and genotyped by MassARRAY platform in Chinese Han population. Odds ratios and 95% confidence intervals were calculated via logistic regression analysis with adjustment in genetic models.

RESULTS

Our results indicated that CYP24A1 variant (rs1570669) was associated with the decreased risk of ischemic stroke (OR = 0.60, p < .001). Stratification analysis showed that the rs6068816 could enhance the ischemic stroke risk by 1.64 times (OR = 1.64, p = .028), while rs1570669 played protective role (OR = 0.63, p = .044) in age >64 years. The rs2762934 had an increased ischemic stroke susceptibility (OR = 1.62, p = .033); however, rs1570669 might reduce stroke risk (OR = 0.61, p = .015) in age ≤64 years. The rs1570669 depressed ischemic stroke susceptibility both in female and male patients (OR = 0.46, p = .002; OR = 0.69, p = .033, respectively), and rs2296241 would weaken the risk in male (OR = 0.63, p = .012). The rs1570669 was associated with decreased risk of ischemic stroke with hypertension (OR = 0.56, p = .042).

CONCLUSION

Our study gave the evidences that CYP24A1 genetic polymorphisms were significantly associated with ischemic stroke patients, which would provide useful information of assessment or possible diagnostic markers for ischemic stroke.

Cerebral small vessel disease due to a unique heterozygous HTRA1 mutation in an African man

Objective

To describe the case of an African patient who was diagnosed with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL).

Methods

Case report and literature review.

Results

We present a 39-year-old Gabonese man who developed progressive gait difficulty at the age of 32, followed by insidious tetraparesis, urinary sphincter disturbance, spastic dysarthria, cognitive dysfunction, and seizures. Brain imaging was performed many years after disease onset and revealed diffuse confluent white matter lesions and lacunar infarcts. He tested negative for acquired white matter disease, but genetic screening detected a genetic variant of HTRA1 gene (G283R), which has not been previously reported.

Conclusions

CARASIL is a disease that usually affects Asian patients. This case report describes a unique case of an African patient diagnosed with CARASIL and a novel genetic mutation in HTRA1 that has not been previously described in the literature.

Genetic Factors of Cerebral Small Vessel Disease and Their Potential Clinical Outcome

Cerebral small vessel diseases (SVD) have been causally correlated with ischemic strokes, leading to cognitive decline and vascular dementia. Neuroimaging and molecular genetic tests could improve diagnostic accuracy in patients with potential SVD. Several types of monogenic, hereditary cerebral SVD have been identified: cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), cathepsin A-related arteriopathy with strokes and leukoencephalopathy (CARASAL), hereditary diffuse leukoencephalopathy with spheroids (HDLS), COL4A1/2-related disorders, and Fabry disease. These disorders can be distinguished based on their genetics, pathological and imaging findings, clinical manifestation, and diagnosis. Genetic studies of sporadic cerebral SVD have demonstrated a high degree of heritability, particularly among patients with young-onset stroke. Common genetic variants in monogenic disease may contribute to pathological progress in several cerebral SVD subtypes, revealing distinct genetic mechanisms in different subtype of SVD. Hence, genetic molecular analysis should be used as the final gold standard of diagnosis. The purpose of this review was to summarize the recent discoveries made surrounding the genetics of cerebral SVD and their clinical significance, to provide new insights into the pathogenesis of cerebral SVD, and to highlight the possible convergence of disease mechanisms in monogenic and sporadic cerebral SVD.

[Genetic characteristics of stroke]

In the recent years there is a growing interest in identification of additional genetic factors of stroke. A growing body of evidence supports the role of genetic factors in determining the risk of both hemorrhagic and ischemic stroke. The article considers the main genes associated with susceptibility to stroke and genetic polymorphisms associated with the disease. Genetic factors, modulating inflammation process, coagulation, lipid metabolism, NO formation, renin-angiotensin-aldosterone system and homeostasis play a significant role in stroke development. A comprehensive analysis of different genes associated with stroke may help to detect individuals with extremely high risk of stroke and implement timely preventive measures to decrease stroke burden.

Characterization of Heterozygous HTRA1 Mutations in Taiwanese Patients With Cerebral Small Vessel Disease

BACKGROUND AND PURPOSE

Homozygous and compound heterozygous mutations in the high temperature requirement serine peptidase A1 gene (HTRA1) cause cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy. However, heterozygous HTRA1 mutations were recently identified to be associated with autosomal dominant cerebral small vessel disease (SVD). The present study aims at investigating the clinical features, frequency, and spectrum of HTRA1 mutations in a Taiwanese cohort with SVD.

METHODS

Mutational analyses of HTRA1 were performed by Sanger sequencing in 222 subjects, selected from a cohort of 337 unrelated patients with SVD after excluding those harboring a NOTCH3 mutation. The influence of these mutations on HTRA1 protease activities was characterized.

RESULTS

Seven novel heterozygous mutations in HTRA1 were identified, including p.Gly120Asp, p.Ile179Asn, p.Ala182Profs*33, p.Ile256Thr, p.Gly276Ala, p.Gln289Ter, and p.Asn324Thr, and each was identified in 1 single index patient. All mutations significantly compromise the HTRA1 protease activities. For the 7 index cases and another 2 affected siblings carrying a heterozygous HTRA1 mutation, the common clinical presentations include lacunar infarction, intracerebral hemorrhage, cognitive decline, and spondylosis at the fifth to sixth decade of life. Among the 9 patients, 4 have psychiatric symptoms as delusion, depression, and compulsive behavior, 3 have leukoencephalopathy in anterior temporal poles, and 2 patients have alopecia.

CONCLUSIONS

Heterozygous HTRA1 mutations account for 2.08% (7 of 337) of SVD in Taiwan. The clinical and neuroradiological features of HTRA1-related SVD and sporadic SVD are similar. These findings broaden the mutational spectrum of HTRA1 and highlight the pathogenic role of heterozygous HTRA1 mutations in SVD.

The pathology and pathophysiology of vascular dementia

Vascular dementia (VaD) is widely recognised as the second most common type of dementia. Consensus and accurate diagnosis of clinically suspected VaD relies on wide-ranging clinical, neuropsychological and neuroimaging measures in life but more importantly pathological confirmation. Factors defining subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes as well as time after the initial vascular event. Atherosclerotic and cardioembolic diseases combined appear the most common subtypes of vascular brain injury. In recent years, cerebral small vessel disease (SVD) has gained prominence worldwide as an important substrate of cognitive impairment. SVD is characterised by arteriolosclerosis, lacunar infarcts and cortical and subcortical microinfarcts and diffuse white matter changes, which involve myelin loss and axonal abnormalities. Global brain atrophy and focal degeneration of the cerebrum including medial temporal lobe atrophy are also features of VaD similar to Alzheimer's disease. Hereditary arteriopathies have provided insights into the mechanisms of dementia particularly how arteriolosclerosis, a major contributor of SVD promotes cognitive impairment. Recently developed and validated neuropathology guidelines indicated that the best predictors of vascular cognitive impairment were small or lacunar infarcts, microinfarcts, perivascular space dilation, myelin loss, arteriolosclerosis and leptomeningeal cerebral amyloid angiopathy. While these substrates do not suggest high specificity, VaD is likely defined by key neuronal and dendro-synaptic changes resulting in executive dysfunction and related cognitive deficits. Greater understanding of the molecular pathology is needed to clearly define microvascular disease and vascular substrates of dementia. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

The first Greek case of heterozygous cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy: An atypical clinico-radiological presentation

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) was previously considered a rare, early-onset recessive form of small-vessel disease (SVD) caused by biallelic mutations in the serine protease gene HTRA1 with subsequent loss of its activity. However, very recently, there is growing interest of research showing heterozygous HTRA1 mutations as causes of SVD with a dominant inheritance pattern. This first Greek heterozygous CARASIL case with unusual clinico-radiological presentation extends our very recent knowledge on how heterozygous CARASIL mutations may be associated with cerebral SVD. Our findings highlight heterozygous HTRA1 mutations as an important cause of familial SVD, and that screening of HTRA1 should be considered in all patients with a hereditary SVD of unknown aetiology.

Genetics of vascular dementia - review from the ICVD working group

BACKGROUND

Vascular dementia is a common disorder resulting in considerable morbidity and mortality. Determining the extent to which genes play a role in disease susceptibility and their pathophysiological mechanisms could improve our understanding of vascular dementia, leading to a potential translation of this knowledge to clinical practice.

DISCUSSION

In this review, we discuss what is currently known about the genetics of vascular dementia. The identification of causal genes remains limited to monogenic forms of the disease, with findings for sporadic vascular dementia being less robust. However, progress in genetic research on associated phenotypes, such as cerebral small vessel disease, Alzheimer's disease, and stroke, have the potential to inform on the genetics of vascular dementia. We conclude by providing an overview of future developments in the field and how such work could impact patients and clinicians.

CONCLUSION

The genetic background of vascular dementia is well established for monogenic disorders, but remains relatively obscure for the sporadic form. More work is needed for providing robust findings that might eventually lead to clinical translation.

Hereditary cerebral small vessel disease and stroke

Cerebral small vessel disease is considered hereditary in about 5% of patients and is characterized by lacunar infarcts and white matter hyperintensities on MRI. Several monogenic hereditary diseases causing cerebral small vessel disease and stroke have been identified. The purpose of this systematic review is to provide a guide for determining when to consider molecular genetic testing in patients presenting with small vessel disease and stroke. CADASIL, CARASIL, collagen type IV mutations (including PADMAL), retinal vasculopathy with cerebral leukodystrophy, Fabry disease, hereditary cerebral hemorrhage with amyloidosis, and forkhead box C1 mutations are described in terms of genetics, pathology, clinical manifestation, imaging, and diagnosis. These monogenic disorders are often characterized by early-age stroke, but also by migraine, mood disturbances, vascular dementia and often gait disturbances. Some also present with extra-cerebral manifestations such as microangiopathy of the eyes and kidneys. Many present with clinically recognizable syndromes. Investigations include a thorough family medical history, medical history, neurological examination, neuroimaging, often supplemented by specific examinations e.g of the of vision, retinal changes, as well as kidney and heart function. However molecular genetic analysis is the final gold standard of diagnosis. There are increasing numbers of reports on new monogenic syndromes causing cerebral small vessel disease. Genetic counseling is important. Enzyme replacement therapy is possible in Fabry disease, but treatment options remain overall very limited.

Stroke Risk Factors, Genetics, and Prevention

Stroke is a heterogeneous syndrome, and determining risk factors and treatment depends on the specific pathogenesis of stroke. Risk factors for stroke can be categorized as modifiable and nonmodifiable. Age, sex, and race/ethnicity are nonmodifiable risk factors for both ischemic and hemorrhagic stroke, while hypertension, smoking, diet, and physical inactivity are among some of the more commonly reported modifiable risk factors. More recently described risk factors and triggers of stroke include inflammatory disorders, infection, pollution, and cardiac atrial disorders independent of atrial fibrillation. Single-gene disorders may cause rare, hereditary disorders for which stroke is a primary manifestation. Recent research also suggests that common and rare genetic polymorphisms can influence risk of more common causes of stroke, due to both other risk factors and specific stroke mechanisms, such as atrial fibrillation. Genetic factors, particularly those with environmental interactions, may be more modifiable than previously recognized. Stroke prevention has generally focused on modifiable risk factors. Lifestyle and behavioral modification, such as dietary changes or smoking cessation, not only reduces stroke risk, but also reduces the risk of other cardiovascular diseases. Other prevention strategies include identifying and treating medical conditions, such as hypertension and diabetes, that increase stroke risk. Recent research into risk factors and genetics of stroke has not only identified those at risk for stroke but also identified ways to target at-risk populations for stroke prevention.

Histopathologic Analysis of Cerebral Autosomal Recessive Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CARASIL): A Report of a New Genetically Confirmed Case and Comparison to 2 Previous Cases

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is a nonhypertensive hereditary cerebral small vessel disease that is caused by mutations in a single gene, HTRA1. The HTRA1 protein normally represses transforming growth factor-β (TGF-β) signaling and its mutations result in vascular changes. Ten homozygous, 1 compound heterozygous, and 1 homozygous frameshift mutation have been identified in the HTRA1 gene of patients with genetically confirmed CARASIL. However, few studies have compared neuropathologic findings in patients with the same or different mutations in HTRA1. We analyzed histopathologic alterations in 3 autopsied patients with genetically confirmed CARASIL: 2 of them had the HTRA1 p.R302X mutation and 1 had the HTRA1 p.A252T mutation. All 3 had similar cerebral arteriopathy showing myointimal proliferation, multi-layering and splitting of elastic laminae, and marked loss of medial smooth muscle cells. One CARASIL patient with the p.R302X mutation had atherosclerosis-like intimal thickening and arteriolosclerosis in the arteries of visceral organs, indicating that atherosclerotic changes are not confined to the intracranial vasculature but can occur throughout the body. CARASIL is a unique hereditary disease that shows similar neuropathology, systemic vascular pathology, and other TGF-β1-related pathology associated with HTRA1 mutation.

Distinct molecular mechanisms of HTRA1 mutants in manifesting heterozygotes with CARASIL

OBJECTIVE

To elucidate the molecular mechanism of mutant HTRA1-dependent cerebral small vessel disease in heterozygous individuals.

METHODS

We recruited 113 unrelated index patients with clinically diagnosed cerebral small vessel disease. The coding sequences of the HTRA1 gene were analyzed. We evaluated HTRA1 protease activities using casein assays and oligomeric HTRA1 formation using gel filtration chromatography.

RESULTS

We found 4 heterozygous missense mutations in the HTRA1 gene (p.G283E, p.P285L, p.R302Q, and p.T319I) in 6 patients from 113 unrelated index patients and in 2 siblings in 2 unrelated families with p.R302Q. The mean age at cognitive impairment onset was 51.1 years. Spondylosis deformans was observed in all cases, whereas alopecia was observed in 3 cases; an autopsied case with p.G283E showed arteriopathy in their cerebral small arteries. These mutant HTRA1s showed markedly decreased protease activities and inhibited wild-type HTRA1 activity, whereas 2 of 3 mutant HTRA1s reported in cerebral autosomal-recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) (A252T and V297M) did not inhibit wild-type HTRA1 activity. Wild-type HTRA1 forms trimers; however, G283E and T319I HTRA1, observed in manifesting heterozygotes, did not form trimers. P285L and R302Q HTRA1s formed trimers, but their mutations were located in domains that are important for trimer-associated HTRA1 activation; in contrast, A252T and V297M HTRA1s, which have been observed in CARASIL, also formed trimers but had mutations outside the domains important for trimer-associated HTRA1 activation.

CONCLUSIONS

The mutant HTRA1s observed in manifesting heterozygotes might result in an impaired HTRA1 activation cascade of HTRA1 or be unable to form stable trimers.