Dennis E. Bulman, PhD
(613)737-8993 (T)
(613) 737-8803 (F)
dbulman@ohri.ca
My laboratory is focused on identifying the cause and understanding the pathophysiology of genetic disorders. Using Linkage analysis and positional cloning strategies, we are attempting to identify the genes for various disorders. Parkinson's Disease
Parkinson's disease (PD) is a complex disorder in which the genetic aspects are only just being realized. Mutations in the synuclein gene have been found to cause PD in a minority of patients, and at least one additional locus on chromosome 2p has been implicated, indicating that PD is a genetically heterogeneous disorder. As with other disorders such as Alzheimer's disease, a number of rare families may be able to provide insight into the genetic and pathophysiological aspects of this disorder.
Dr. David Grimes and I are collaborating on a number of genetics projects involving patients with Parkinson's disease. We are also part of a larger group, The Parkinson Research Centre (PRC) at the University of Ottawa. The PRC brings together a number of basic scientists who provide a multidisciplinary approach to Parkinson's research.
Our projects include association studies involving DNA samples collected from more than 250 Parkinson's patients as well as a linkage study involving a large French Canadian kindred with Parkinson's disease.
Brachydactyly A-1: What we have done.
The cost of tissue damage due to degenerative disease such as arthritis is enormous in terms of health care costs, lost economic productivity, diminished quality of life. Advances in cell, developmental and molecular biology, and the discovery of early mediators of bone development, have given impetus to systematic investigations that will lead us to viable treatment options and potentially to the regeneration of these tissues by cell transplantation or the pharmaceutical induction. A significant avenue of research towards this goal is the identification and characterization of genes and their products which are involved in the early stages of bone development. The brachydactylies are a group of congenital malformations that affect normal bone development resulting in shortened digits. They are categorized into a number of different types based on the bones and digits involved. Brachydactyly type A1 (BDA1) is characterized by bilateral shortness of the middle phalanges in digits two through five. BDA1 has the distinction of being the first human trait described in terms of autosomal dominant Mendelian inheritance. Despite this, little was known about the genes involved until a group from China identified mutations in the Indian Hedgehog gene. We followed their report with the identification of a second locus responsible for BDA1. A synopsis of our work on this project is listed below.
(1) That BDA1 is linked to an 11 cM critical region on chromosome 5p13.2-13.3 in a four-generation family affected with BDA1. A maximum lod score of 6.91 at D5S477 was attained at a recombination fraction of 0.00. Haplotype analysis provided evidence for an 11 cM critical region that cosegregates with the disease. The distal end of this critical region occurred between markers D5S819 and D5S1986. The proximal boundary occurred between markers D5S1506 and D5S663. The location of the disease locus within the region between D5S819 and D5S1506 was further supported by multipoint linkage analysis (Armour, et al., 2002). OMIM has designated this locus BDA1B (607004). Since our publication, the pedigree has expanded appreciably and as a result the region has now been reduced to 7 cM through the addition of more than 20 family members.
(2) Early in the 1900s Dr. Harry Drinkwater described a number of British families with BDA1 (Drinkwater, 1908; Drinkwater, 1915). We obtained DNA from the descendents of two of these families. Although they were not known to be related, both share a common mutation within the Indian hedgehog gene (IHH). This novel mutation is a guanine to adenine transition at nucleotide 298, resulting in an p.Asn100Asp amino acid substitution. Both families demonstrate significant intrafamilial phenotypic heterogeneity among the affected individuals. Examination of single nucleotide polymorphisms (SNP) has shown that the affected individuals in both families share SNPs within IHH consistent with that of a common founder. The identification of the same mutation in these families has answered a question that is nearly a century old about the genetic cause of their disease and supports the hypothesis that IHH plays a pivotal role in normal human skeletogenesis (McCready, et al., 2002).
(3) In collaboration with Hope Northrup's laboratory (University Texas Southwestern), we identified a novel mutation in the IHH gene in one family and excluded IHH and the 5p locus in another family, thereby implicating a potential third locus for BDA1 (Kirkpatrick, et al., 2003). Unfortunately, the latter family is too small to support a genome screening approach to identify this third locus.
(4) One hundred years ago William C. Farabee, as a Harvard graduate student, described the inheritance pattern of BDA1 in terms on Mendel's newly rediscovered laws. This made BDA1 the first human disorder described in terms of autosomal dominant Mendelian inheritance (Farabee, 1903). We obtained DNA samples from descendants of this historically relevant family and went on to demonstrate that this family not only had the same mutation as Drinkwater's families, but that Farabee's family was also related to the families described by Drinkwater (McCready et al., 2005).
A number of collaborators are involved in this project. Clinical collaborators include Dr. Sarah Nikkel from the Children's Hospital of Eastern Ontario and Dr. Jennifer MacKenzie, Queen's University. Dr. Rashmi Kothary is helping us generate a transgenic model of BDA1. In addition, Dr. Valerie Wallace from the OHRI is a co-applicant on our funded project. Dr. Wallace provides us with the needed expertise in hedgehog signaling and biochemical analysis of mutated hedgehog molecules.
Funding for our work on Brachydactyly is being provided to Dr. Bulman (P.I.) by a research grant from CIHR.
Myoclonus Dystonia: What we have done.
Inherited myoclonus dystonia (IMD) is an autosomal dominant form of myoclonus and dystonia and is characterized by rapid muscle contractions (myoclonus) affecting predominantly the neck, shoulders and arms, and sustained twisting and repetitive movements resulting in abnormal postures (dystonia). Symptoms normally begin in the first or second decade of life and classically have no other associated features with the possible exception of subtle psychiatric symptoms (obsessive-compulsive disorder).
Our initial work involved excluding possible candidate genes for IMD in a large 5 generation Canadian kindred (Grimes et al. 2001). Subsequently we mapped a locus for IMD to 18p11 based on a complete genome scan of this family. These results were published (Grimes et al., 2002) in the journal Neurology and the article was accompanied by an editorial. This locus has been designated DYT15 and has the MIM #607488. Currently we have refined the IMD locus to a 2.1 Mb interval on 18p11, a region which contains only 10 known and predicted genes.
As mutations in the coding region of the -sarcolglycan (SGCE) genes were also shown to cause IMD, we implemented routine screening of SGCE for mutations in all probands. In one family we identified a novel 5 base pair deletion in exon 7. We have also identified a p.R102X mutation in two other families (Han et al. 2003). Both of these mutations disrupt the extracellular domain of SGCE. PCR direct sequencing of eight other families did not reveal any mutations in the exons nor flanking introns of SGCE. In total, we have collected blood and isolated DNA from thirteen families who meet diagnostic criteria for IMD and we are in the process of collecting blood samples from another 4 families and 8 sporadic cases.
The mechanisms causing most types of hyperkinetic movements are poorly understood and this lack of knowledge is reflected in the poor efficacy of most currently available treatments. Studying the genetic forms of such diseases has resulted in a marked improvement in understanding the basic pathophysiological processes of these conditions. The identification of a novel gene for myoclonus dystonia will not only improve our understanding of abnormal involuntary movements but will also improve our understanding of basal ganglion function and neuromuscular disease.
IMD is a genetically heterogeneous disorder with only two loci responsible for the disorder. The one known disease gene, -sarcoglycan (SGCE) maps to 7q21 and has the designation DYT11. Approximately 40% of IMD patients demonstrate a mutation in SGCE. The second locus, DYT15 was identified in our laboratory and maps to 18p11.
To date, six sarcoglycan genes have been cloned in human and mouse. Mutations in sarcoglycan are responsible for autosomal recessive limb-girdle muscular dystrophy. All six sarcoglycans are expressed in striated muscle, while - is not expressed in smooth muscle. Of the sarcoglycans, only - is found in the brain. SGCE shares 44% amino acid identity with -sarcoglycan. SGCE is expressed, within heart, lung, intestine, spleen and peripheral nerve and has also been shown to be widely expressed in rat brain throughout development into adulthood and is thought to contribute to neuronal structure in the adult central nervous system.
This work is being performed in collaboration with Dr. David A. Grimes (co-applicant of our funded research). Dr. Grimes is a Neurologist with a specialty in movement disorders. The generation of animal models is being performed in collaboration with Drs. Rashmi Kothary and Michael Rudnicki.
Funding for our work on myoclonus dystonia is being provided to Dr. Bulman (P.I.) by a research grant from CIHR.
The Centre for Applied Genomics
I am the Scientific Director of the Genotyping Core facility for The Centre for Applied Genomics. The Director of TCAG is Dr. Stephen Scherer (Hospital for Sick Children). http://tcag.bioinfo.sickkids.on.ca/ This is a Genome Canada funded endeavor, where my laboratory performs microsatellite genome screening and training on a cost recovery basis.
In addition, I am funded by the Ontario Research Development Challenge Fund. Our project entitled "A provincial program in disease gene discovery" for which I am the P.I. and the co-applicants include Drs. R. Hegele, K. Siminovitch, P. Ray and S. Scherer, provides much of the infrastructure for the various laboratories.
Members of the Lab
Graduate Students
Fabin Han
Alison Grimsey
Lita McDonald
Ashley Byrnes
Post Doctoral Fellows
Fengxia Xiao
Research Technicians
Lemuel Racacho
Heather MacDonald
Roubing Zou
Kelly Westaff
Collaborators:
Dr. David Grimes
