McCredie, Janet

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Janet McCredie devised the theory of Neural Crest Injury as being the pathogenesis of congenital malformations of the thalidomide type. She was also one of the instigators of NSW Breast Screen which enabled her to help bring to fruition her mother’s initial ideas for mammography as a screening technique for early diagnosis of breast cancer.

Janet grew up knowing about radiology. Her father was an obstetrician and her mother, Marjorie Dalgarno (also profiled in this section) was one of the early pioneers of radiology in Sydney.

Janet graduated from Medicine in 1959 and began working as a Resident Medical Officer at Rachel Forster Hospital that year. She completed her postgraduate studies in Radiology in UK, and was made a Fellow of both the UK College and the Australasian College of Radiologists. From 1965 to 1972 Janet was Staff Radiologist at the Royal Prince Alfred Hospital, Sydney, becoming a Senior Staff Radiologist in 1973, then VMO until 2000. Throughout this time, Janet also continued to work on her days off in her mother’s private practice in Campsie.

Investigating radiographs of thalidomide children, she worked out how thalidomide acts to cause malformations in the newborn, and uncovered a previously unrecognised mechanism of embryogenesis:

Briefly, around 1970, I was asked to look at the X-rays of thalidomide children. They had the most grotesque deformities of bone and joints I had ever seen. When I started reading the literature, I found that nobody had ever really worked out what the target organ was for the drug, what tissue it damaged within the embryo. I interpreted the X-rays as being subtractions of segmental areas of nerve supply.
Thalidomide was a sensory neurotoxin, and what I was looking at was a disease with a sensory nerve distribution. It seemed logical that the sensory neurone could be the cell in the embryo that the drug was targeting. The cell belongs to the neural crest group. So I devised the theory of Neural Crest Injury as being the pathogenesis of congenital malformations of the thalidomide type. The theory not only applies to limb deformities but also to congenital heart abnormalities, deformities of the gastro-intestinal system and all other systems – except the central nervous system.[1]

Janet’s findings were published in The Lancet in 1973, and in the Medical Journal Australia in 1974. Shortly after, she presented her theory during one of the ‘Grand Rounds’[1] at Royal Prince Alfred Hospital. Janet says she remembers it creating “quite a buzz” in the hospital. She was later awarded an MD by the University of Sydney for the thesis “Neural Crest Defects”, and in recognition of the importance of this discovery.

From 1975, she reduced the hours she spent as a practitioner of radiology to enable her to take up a Senior Lectureship in Surgery (Diagnostic Radiology) at the University of Sydney, but remained a Visiting Radiologist at both the Royal Prince Alfred Hospital and the Royal Alexandra Hospital for Children. In 1980 she became Associate Professor of Radiology within the Department of Surgery at the University.

Unlike her mother, she was not “interested in machinery” but did “attend the first CT scan conference in Australia because [she] thought it was such a fantastic tool”. She was also interested in the development of ultrasound. As is noted in her mother’s profile, the technology of mammography in the 1960s initially delivered too high a dose of radiation to warrant the use of multiple exposures for screening purposes within the general population.

However, by the 1980s the technology had improved. In 1986 the results of a study by Professor Sir Patrick Forrest (on whether or not to implement a population screening programme in the UK) were published[1], and screening for breast cancer using mammography became a real possibility in Australia. Continuing her mother’s legacy, Janet was one of the five doctors from Royal Prince Alfred Hospital who convinced the NSW Minister for Health of the value of population screening for breast cancer and secured a Ministerial grant to fund a pilot study. Janet reflects:

Having seen mobile vans in Japan with fluoroscopy units to detect early gastric cancer in rice paddy farmers, and mobile vans with CT units driving through the rural hamlets of Wisconsin, USA, I believed that the Australian community would be best examined by mobile mammography vans, like the anti-TB chest units of old. I helped a young doctor from the NSW Department of Health to design the first mobile van and to determine the essential radiological processes to be set up both in the vans and at the base.[1]

When the question of appointment of a director for the breast screening project came up, Janet suggested that Dr Mary Rickard, whom she knew as a friend, scientist and radiologist apply. According to Janet, Rickard “has become a national teacher and world expert in the field”.

It was wonderful for Janet to see her mother’s idea come to fruition, but by this stage, her own research and academic interests had begun to drive the direction of her work. During her time as an academic Janet strove to increase the importance given to radiology as a diagnostic tool within the curriculum. She says:

I never wanted to create mini radiologists, but I did want to ensure that future clinicians understood the indications, contra-indications, preparations, costs, and complications of the tests they order. This was applied physiology, not pictures… I was able to introduce students to the physics of the X-ray beam, radiation safety, and the principles of black, white and grey scale and the complete range of imaging tests and their principles… There are two important junctions for learning to visualise in organ imaging. The first is to learn normal anatomy and imaging together. The second is to couple macroscopic pathology with organ imaging of that disease. But Pathology lecture time on campus was reduced in the five year curriculum so I obtained permission to put miniaturised X-ray films beside the bottles in the Pathology Museum. I brought some miniature view boxes back from Chicago. My radiographer made 100mm copies of films which I had selected to match the conditions illustrated in the bottles. We set this up with the assistance of the pathologists and their technicians, so that any interested student could absorb the pathology and its image at the same time.[1]

Concurrently with her appointment within the Faculty, Janet was appointed Senior Education Officer in the NSW Branch of the Royal Australasian College of Radiologists, a role which encompassed the planning of postgraduate courses for radiologists.

Throughout her career, Janet has maintained an interest in fostering the teaching of radiology and was responsible for the purchase of a $20,000 Film Library which was housed within the College of Radiologists.

In the Neurological Laboratory at Sydney University, her research team identified quantitative changes in peripheral nerves of newborn rabbits, thus establishing the site of thalidomide’s action as the neural crest. Kathryn North and Gillian Dunlop were leading researchers doing BSc Med degrees on this project. Professors J G McLeod, J Pollard, P Armati, Sue Dorsch, and P McGrath gave critical advice and support throughout these investigations. Dr John Cameron showed nerve axons in embryonic limb buds by electron microscopy for his PhD. Rose Shoobridge proved that neural crest injury in chick embryo results in longitudinal limb deformities for her MSc. Drs Jane Elliott, Jill Forrest and Anne Kricker did a case control study of children born with limb reduction defects in a decade in New South Wales.

As a result of her research, she was elected to Membership of the International Skeletal Society, which has enabled collaborative and ongoing research into thalidomide embryopathy, especially with Professor Hans Willert in Germany. With the Marcus Singer Symposium she is a member of a small group of international biologists who work on regeneration of limbs, mainly in amphibia. This association with biologists has enabled her to further develop her theories of birth defects.

In 1994, Janet was made a Member of the Order of Australia for services to diagnostic radiology and medical research.Janet remained Associate Professor until her retirement from the University of Sydney in 1990, and was made an Adjunct Associate Professor thereafter. She retired from private practice in 1996, and from Royal Prince Alfred Hospital four years later.

Janet has been a staunch supporter of women’s education and has maintained a long association with the Women’s College, University of Sydney since her own residency there as a student. She has been a Member of Council since 1965, serving as Honorary Secretary, Deputy Chairman (to Marie Bashir) and Chairman for eight years. She then served another five years as Deputy Chairman and has now taken on the Chair again – “despite my protestations that my shelf life had expired” – as the previous Principal, has been appointed Governor of Queensland. She hopes to ‘bow out’ when her successor has been settled in.

Since 2001, Janet has been writing a book on Neural Crest Defects.

Citation: Mellor, Lise (2008) McCredie, Janet. Faculty of Medicine Online Museum and Archive, University of Sydney.

An alternate version appears in: Mellor, L. 150 Years, 150 Firsts: The People of the Faculty of Medicine (2006) Sydney, Sydney University Press.