The main research interests are in molecular genetics of dyslipidemias, atherosclerosis, and other causes of sudden death, genetic epidemiology of arteriosclerotic cardiovascular disease and drugs affecting lipid metabolism.
Molecular Genetics of Familial Hypercholesterolemia (FH)
Our studies have shown that in Israel, FH is associated with at least fourteen different LDL receptor gene mutations. Four unique mutations are responsible for a large number of the known cases. The proliferation of these four different LDL receptor mutations is related to founder mechanisms. DNA samples from hundreds of FH families are currently available in our DNA bank. We have also developed specific assays in order to directly detect these mutations in DNA samples obtained from FH patients.
Molecular Genetics of Cerebro-Tendinous Xanthomatosis (CTX)
CTX is an autosomal recessive lipid storage disease caused by mutations in the sterol 27-hydroxylase (CYP27) gene. The clinical hallmarks of the disease include tendon xanthomas, premature atherosclerosis, juvenile cataracts and progressive neurological dysfunction. CYP27 was cloned in our laboratory. Following the characterization of CYP27, three distinct mutations have been identified in Jews of North African origin. The phenotypic expression of mutations in CYP27 vary between families and even within families. Collaborative studies with other research teams from England, France, South Africa, the USA, Australia and Hong Kong has revealed the extensive molecular heterogeneity of CTX in the world. So far 20 novel CYP27 mutations were identified in our laboratory.
Establishment of a CYP27 Knockout Mouse Model
We have cloned the mouse CYP27 gene and designed a targeting plasmid. The construct was designed to disrupt CYP27 by inserting a selectable marker into one of its exons via homologous recombination. Our targeting plasmid was introduced into mouse embryonic stem cells (ES cells). ES cells with a modified CYP27 gene were reintroduced into host blastocysts and germline transmission of the mutant gene. The phenotypes of the animals harboring the mutant gene were studied through the analysis of the resulting metabolic abnormalities and pathological changes. These animals are currently used in several international collaborative projects with our laboratory.
Identification of a Cholesterol Lowering Gene (CLG)
We have recently studied a family with familial hypercholesterolemia (FH) whose members has lower-than-expected LDL-C levels. The existence of CLG was proven by linkage analysis, which identified a locus at 13q. We found strong evidence for linkage at this locus with LDL, HDL, total cholesterol, and body mass index. The data provided support for the existence of a novel gene influencing lipid concentrations in man. Currently, CLG is mapped to a region of approximately 10 centimorgan. Further mapping is underway.
We used three main strategies:
Identification of additional haplotypes associated with low LDL-C levels through the study of other populations.
Use of Single nucleotide polymorphism (SNP) analysis in order to identify gene or point mutations associated with low LDL level phenotype.
Identification of specific tissues with highest expression of CLG by< using metabolic turnover studies in order to confirm the identified gene expression product activity with the particular members of the family carrying the particular phenotype.
MED PED (Make Early Diagnosis Prevent Early Death) FH (familial hypercholesterolemia) Program
FH is an autosomal dominant disease manifested by extremely high plasma cholesterol levels leading to premature morbidity and mortality from cardiovascular diseases. The main purpose of the MED PED program is to identify and study patients and families with FH. These families are registered in a specific database, maintained at our center. Clinical diagnosis of FH is supported by the analysis of the specific LDL receptor gene mutations. We provide therapy through the outpatient lipid clinic. The patients are also involved in clinical trials testing new drugs for hypercholesterolemia.
Treatment of FH with HMG CoA Reductase Inhibitors
The efficiency, tolerability and safety of lipid lowering drugs either alone or in combination with other lipid lowering drugs is tested in our center on high risk patients with FH. We have conducted several consecutive studies using HMG CoA reductase inhibitors in patients with FH. These studies, phase II-IV, include a dose finding pharmacogenetic single-blind study, several high dose, double blind studies and drug combinations. We were the first to use molecular genetic characterization of FH patients on a drug trial and document that constitutional, genetic and familial determinants, control the response of plasma lipids and lipoproteins to statins.
Establishment of a Shared Database for Patients and Families with Cardiomyopathies Affiliated with The European Working Group on Myocardial Diseases
These primary heart muscle diseases represent an important cause of cardiac morbidity and mortality in developed countries. Specific mutations responsible for the disease had been so far identified only in hypertrophic cardiomyopathy (HCM). Genetic typing is expected to solve major preclinical diagnostic, prognostic, preventive, behavioral and family counseling questions which can not be solved by clinical research. Israeli researchers from all major medical centers are members of this concerted action, which coordinates Israeli clinical and molecular research of the epidemiological, clinical and genetic aspects of CM. The research includes creation of a standardized database of patients with CM (Dilated, Hypertrophic, Restrictive, Right Ventricular Arrhythmogenic and Unclassified) and a DNA bank for patients with the familial form of CM as well as analysis of gene markers (microsatellites) as well as known mutations in four candidate genes.