Colloquium with Marcy MacDonald, PhD, Massachusetts General Hospital, Harvard Medical School

Huntington’s disease, a dominantly inherited neurodegenerative disorder, is characterized by progressively worsening motor disturbances, cognitive decline and behavioral signs and loss of neuronal cells, initially in the deep brain structures (caudate and putamen). The singular genetic cause of the disorder is an expanded, unstable CAG triplet repeat located in the HD gene (HTT), that encodes a stretch of polyglutamine in a large HEAT-repeat protein (huntingtin). Deep Huntington’s disease natural history studies, such as PHAROS, COHORT, PREDICT-HD, TRACK-HD, and ENROLL-HD, have fueled genetic searches for the DNA sequence variants that influence the ratelimiting steps in the decades-long disease process. Huntington’s disease modifier genes now provide insights into the driver of the timing of onset of clinical signs and begin to dissect the relationships between phenotypes that can be measured before and after the onset of overt clinical signs. The genetic paradigm provides a guide for studies in other brain disorders and the specific findings in Huntington’s disease have implications for the pathogenesis of other triplet repeat disorders, including the notion that these should be considered to be ‘polyglutamine diseases’.

Dr. MacDonald obtained her Ph.D. in Medical Biophysics at the University of Toronto in 1980 and did Post-doctoral training at the Medical Research Council (Mill Hill, U.K.) and the University of Amsterdam (The Netherlands). Dr. MacDonald currently is a Professor of Neurology at the Harvard Medical School and Geneticist (Neurology Service) in the Molecular Neurogenetics Unit (Center for Genomic Medicine) at the Massachusetts General Hospital. Dr. MacDonald is also a faculty member of the Basic Biological Sciences Program at the Harvard Medical School and is an Associate Member of the Eli and Edythe L. Broad Institute of MIT and Harvard.

Dr. MacDonald’s research on inherited human brain disorders follows a collaborative human genetic research cycle paradigm that is anchored by data-driven approaches. Genetic studies with human patients identify the root cause of the disorder; the initial biological consequences of the mutation are identified in experimental systems created to precisely replicate the human mutations; and, returning to genetic studies with human patients, the genes that modify features of the disease caused by the primary mutation are identified, thereby providing data-driven information to improve diagnosis and disease management as well as gene- and biological pathway-based targets for the development of therapeutics. Over the past thirty years, Dr. MacDonald has been involved in the discovery of the genetic variants that cause autism, Neurofibromatosis 2, Hereditary Spastic Paraparesis, and several neurodegenerative disorders, including Huntington's disease, Neuronal Ceroid Lipofuscinosis, and Parkinson disease, though over this time the sustained focus has been on Huntington’s disease, with its unstable CAG triplet repeat expansion mutation in the HD gene on chromosome 4.

Dr. MacDonald’s research is reported in more than 250 publications and has been supported by grants from the National Institutes of Health (National Institute of Neurological Disease and Stroke, National Institute of Child Health and Human Development, National Institute of General Medical Sciences), the Huntington Society of Canada, the Huntington’s Disease Society of America and the CHDI Foundation, Inc.

Host

Myriam Heiman

Organizer

Brittany Greenough