Research Projects

Our lab has several ongoing research projects.

Genetic factors in ischemic stroke

Smoking or being the first-degree relative — such as a parent, an aunt, a grandparent or a cousin — of someone who has had a stroke is reported to independently almost double the risk of ischemic stroke. These findings support our hypothesis that stroke is a result of an intricate interplay between genes and the environment.

Our study on genetic factors in ischemic stroke is investigating this relationship between environmental and genetic factors. We have collected DNA samples from nearly 2,000 people who had an ischemic stroke and were part of a study of vitamin intervention for stroke prevention. Our study also has 2,000 ethnically matched control participants without stroke. Our study marks the first time a study of this magnitude has been undertaken.

We have detailed phenotypic information about our participants who have had strokes. These samples are being examined for genetic determinants, taking into account the confounding factors of obesity, diabetes, hypertension, smoking, age and sex.

Genetic associations with ischemic stroke remain contentious. With our large sample collection, though, we're confident that we can assess the influence of these genetic variants on risk in the U.S. population. Establishing the joint effects of smoking and genetics will help identify subsets of at-risk individuals and help with preventive diagnosis and treatment. This information also will be the driving force behind the generation of both in vitro and in vivo model systems that will allow safety and efficacy profiling in the development of targeted therapeutics.

Familial stroke

The most successful approach to mapping stroke-related genes has been the identification of rare Mendelian forms. The classical linkage method using large familial aggregates that display patterns of stroke inheritance — dominant or recessive — has identified genes involved in monogenic forms of disease. Cerebral autosomal dominant arteriopathy with subcortical infarctions and leukoencephalopathy (CADASIL) is a rare form of small vessel occlusive disease.

Pathogenic mutations in the NOTCH3 gene (OMIM*600276) were observed to result in CADASIL. Three genes have been identified as producing hemorrhagic stroke because of cerebral cavernous malformation. Cerebral cavernous malformation causes vascular capillary abnormalities that easily rupture. Microtubule-associated protein krev interaction trapped 1 (KRIT1; OMIM*604214) was found to harbor rare familial mutations. Subsequently, a novel gene (MGC4607 [OMIM*607929]) similar to ICAP1α, a KRIT1 binding partner, was identified as causing cerebral cavernous malformation. The third gene is the programmed cell death gene 10 (OMIM*609118).

Our lab is working to develop a molecular genetics familial stroke database at Mayo Clinic in Jacksonville, Florida. Our hypothesis is that the identification of groups of related people, called kindreds, who have a family history of stroke will, through classical linkage studies, lead to identification of new genes that when mutated effect a stroke phenotype.

Through ongoing clinical stroke research by Mayo Clinic neurologist James F. Meschia, M.D., our lab has identified 275 initial family members, called probands, who report a family history of stroke and have already donated DNA in a case-control study. We are screening these family members for known variants associated with stroke. Other affected and unaffected family members also are being included.

Familial CADASIL gene NOTCH3 in ischemic stroke

One approach to mapping stroke-related genes has been the identification of rare Mendelian forms. The classical linkage method using large familial aggregates that display patterns of stroke inheritance — dominant or recessive — has identified genes involved in monogenic forms of disease. Pathogenic mutations in the NOTCH3 gene (OMIM*600276) are observed to result in cerebral autosomal dominant arteriopathy with subcortical infarctions and leukoencephalopathy (CADASIL; OMIM*125310), a form of small vessel occlusive disease.

Lessons from other disorders, such as Alzheimer's disease and Parkinson's disease, have demonstrated that often the sporadic forms of disease may be influenced by less penetrant pathogenic genetic variation in the familial genes. Interestingly, NOTCH3 mutations have been observed in a patient with vascular dementia and in an older patient mildly affected by sporadic stroke. The oldest identified patient with CADASIL was 94 years old. The pathomechanism behind NOTCH3 mutations causing ischemic stroke in CADASIL still isn't clearly defined.

Our project on the familial CADASIL gene NOTCH3 in ischemic stroke is exploring the relationship among NOTCH3 genetic variants that we hypothesize to increase susceptibility to ischemic stroke.

Establishing the effects of NOTCH3 variability and exploring this with environmental factors such as smoking may help identify subsets of at-risk individuals and promote preventive diagnosis and treatment. The genetic variants influencing stroke susceptibility also may be the driving force behind the generation of both in vitro and in vivo model systems, which will allow safety and efficacy profiling in the development of targeted therapeutics.

Individualizing the ischemic stroke genome

Genomewide association studies have proved effective in the identification of common genetic determinants in disease. Nevertheless, this research doesn't account for influence of the approximately 16.5 kb of closed circular mitochondrial genome (mtDNA). The mitochondrial organelle is composed of both nuclear-encoded proteins and mtDNA-encoded proteins. Its dysfunction is hypothesized to play a prominent role in age-associated neurologic degeneration.

Our lab is conducting sequence and copy number analysis of the entire 16.5-kb mtDNA genome to complement our existing genomewide association study in ischemic stroke. We're using Affymetrix mtDNA resequencing arrays and lymphocyte-derived DNA from our North American Caucasian concordant sibling pairs with ischemic stroke. We're performing association analysis of mtDNA genetic variability contributing to ischemic stroke. Identified genetic mtDNA variability is validated in larger series of people with ischemic stroke and with unaffected control participants.

The scientific aim of our proposal is to identify variation within the mtDNA genome that associates with ischemic stroke. Associated variants may inform the development of functional cellular or animal models, act as preclinical biomarkers, define high-responder populations in clinical trials, and direct future first-in-class pharmacotherapeutic intervention strategies.

Genetic factors in vascular dementia

Data from population-based studies using neuroimaging estimate that each year more than 11 million people in the United States have a stroke that doesn't cause any apparent symptoms, a so-called silent stroke. The extent of the impact of this silent disease on public health remains unclear, but it's likely that this condition contributes to cognitive dysfunction.

Vascular dementia is the second most common form of dementia after Alzheimer's disease. The cognitive symptoms of vascular dementia are heterogeneous and most likely reflect the interaction of both environmental and genetic factors. Our research team is examining brain tissue for gene expression and genetic variants that increase the risk of vascular dementia.