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About Sickkids
About SickKids

Walter Kahr, MD, PhD, FRCPC

The Hospital for Sick Children
Staff Physician

Research Institute
Senior Scientist
Cell Biology

University of Toronto
Departments of Paediatrics and Biochemistry

Phone: 416-813-7977
Fax: 416-813-5327
Email: walter.kahr@sickkids.ca

For more information, visit:

The Kahr lab

Brief Biography

Dr. Kahr received his MD and PhD (Biochemistry) from the University of Toronto in 1994. Following post-graduate training in Internal Medicine at the University of Toronto (1994-1997), Dr. Kahr completed a haematology fellowship in the Department of Medicine (1997-1999) and a post-doctoral fellowship in the Department of Pathology and Molecular Medicine (1999-2002) at McMaster University in Hamilton. During his post-doctoral fellowship, Dr. Kahr discovered that the underlying inherited bleeding defect in the Québec platelet disorder was the abnormal expression of urokinase in patient platelets.

Dr. Kahr joined the Division of Haematology/Oncology at The Hospital for Sick Children (SickKids) in 2003 as a Clinician-Scientist. He has set up a research laboratory in the Cell Biology Program and is the recipient of a Phase II Clinician Scientist Award from the Heart and Stroke Foundation of Ontario. Dr. Kahr's clinical interests are in the field of haemostasis and thrombosis and his research focus is on the development and function of platelets in health and disease.

Clinical Activities

  • Staff physician in the Division of Haematology/ Oncology at SickKids
  • Staff consultant to the Department of Paediatric Laboratory Medicine at SickKids
  • Co-Director of the of the Clinical Haemostasis Research Laboratory at SickKids
  • Coagulation consultant for paediatric patients implanted with a Berlin Heart Ventricular Assist Device
  • Care of paediatric patients with abnormal bleeding and clotting disorders
  • Utilization of global haemostatic assays in paediatric patients with bleeding and clotting disorders
  • Clinical Director of the Association of Hemophilia Clinical Directors of Canada (AHCDC)
  • Member of the Rare Inherited Bleeding Disorder Subcommittee of the AHCDC
  • Member of the Canadian Pediatric Thrombosis and Hemostasis Network (CPTHN)

Research Interests

  • Inherited platelet function defects
  • Mechanisms of megakaryocyte and platelet granule formation and secretion
  • Role of VPS33B in megakaryocyte amd platelet alpha granule biogenesis
  • Role of platelets and the complement system in atypical hemolytic uremic syndrome (collaboration with Dr. Christoph Licht)
  • Role of defective myosin IIA in patients with MYH9-related disorders
  • Biosynthetic ability of platelets in health and disease

Research in my laboratory is aimed at understanding the development and function of platelets in health and disease. Platelets are small blood cells that initiate and coordinate blood clotting at wound sites, where they adhere, aggregate and secrete an assortment of molecules in the process of blood clotting. Platelets are also involved in the formation of arterial plaques and pathological clots, such as the arterial thrombi that cause acute coronary syndromes and ischemic stroke, which are both major causes of mortality in the modern world.

To gain insights into the mechanisms of platelet development and function we are studying patients with inherited platelet disorders. A recent investigation into a severe multisystem disorder (ARC syndrome) led to the identification of the protein VPS33B, which is required for the formation of platelet and megakaryocyte alpha granules. Understanding the mechanisms of VPS33B-mediated platelet alpha granule formation is a current focus in my laboratory.

VPS33B is a member of the Sec1/Munc18 protein family, predicted to interact with SNARE proteins to facilitate docking and fusion of intracellular vesicles. This protein is expressed in numerous tissues and is associated with late endosomes/lysosomes in mammalian cells. Efforts are underway to identify potential VPS33B binding proteins. Candidate proteins are currently being evaluated using a combination of molecular, cellular and biochemical approaches. RNAi techniques are being utilized to evaluate the loss of VPS33B function in human megakaryocytes. Candidate VPS33B binding proteins are also being knocked down using RNAi to assess their role during alpha granule biogenesis.

There are a number of collaborative studies ongoing in my laboratory. In collaboration with SickKids nephrologist Dr. Christoph Licht, we are investigating the role of the complement system and platelets in the pathogenesis of atypical hemolytic uremic syndrome (HUS). We are also investigating the role of myosin IIA function in platelets and megakaryocytes by examining a cohort of children with MYH9-related macrothrombocytopenia. Another area of research is investigating the recently discovered biosynthetic ability of platelets in health and disease.

External Funding

  • Canadian Institutes of Health Research (CIHR), Operating Grant
  • Heart and Stroke Foundation of Canada (HSFC), Grant-in-Aid, Co-Investigator
  • Heart and Stroke Foundation of Ontario (HSFO), Phase II Clinician Scientist Award
  • CIHR Training Program in Protein Folding and Interaction Dynamics: Principles and Diseases, Training Grant, Co-Investigator
  • Bayer Inc., Investigator Sponsored Study Grant


  • The American Society of Hematology Travel Award, 1998, 2000
  • Canadian Institutes of Health Research/Heart and Stroke Foundation of Canada Post Doctoral Fellowship, 1999
  • Canadian Hematology Society Royal College of Physicians and Surgeons of Canada - Amgen Research Award, 1999
  • University of Toronto Dean's Fund New Staff Grant Competition Award, 2005
  • Heart and Stroke Foundation of Ontario (HSFO), Phase II Clinician Scientist Award, 2006


For a complete listing of Dr. Kahr's papers visit Pub Med.