The Principles of Teratology: Are They Still True?
Jan M. Friedman*
Department of Medical Genetics, University of British Columbia, and Child & Family Research Institute, Vancouver, Canada
Received 23 March 2010; Revised 8 May 2010; Accepted 12 May 2010
James Wilson originally proposed a set of ‘‘Principles of Teratology’’ in 1959, the year before he helped to
found the Teratology Society. By 1977, when these Principles were presented in a more definitive form in
Wilson and Fraser’s Handbook of Teratology, they had become a standard formulation of the basic tenets of
the field. Wilson’s Principles have continued to guide scientific research in teratology, and they are widely
used in teaching. Recent advances in our knowledge of the molecular and cellular bases of embryogenesis
serve only to provide a deeper understanding of the fundamental developmental mechanisms that underlie
Wilson’s Principles of Teratology. Birth Defects Research (Part A) 88:766À768, 2010. Ó 2010 Wiley-Liss, Inc.
Key words: Principles of Teratology, James Wilson, history of teratology
A remarkable conference was held on April 5, 1959.
Because of the recent successful development of a vaccine
against polio virus, the National Foundation, which
up to that point had supported research only on poliomyelitis,
decided to broaden its focus. The organization,
the predecessor of today’s March of Dimes Foundation,
began working to understand and prevent congenital
anomalies. Consequently, a conference was held to
review the current state of knowledge in the field for the
Foundation’s medical advisory committees (Rivers, 1959).
This conference on ‘‘congenital malformations’’ (‘‘birth
defects’’ had not yet been adopted as the descriptor of
choice) brought together recognized leaders in the field.
Their talks, which were published in the Journal of
Chronic Diseases later that year (Table 1), provide insight
into the scientific thinking of the founders of the Teratology
Society at the time it was being organized. Moreover,
the paper presented by James Wilson includes the first
formulation of his Principles of Teratology (Table 2),
which he put forward very tentatively: ‘‘After careful
deliberation, and no little vacillation, as many as five
generalities emerge which seem to be applicable to most
teratologic situations. It is certainly premature to formulate
these as universal laws of teratology. They are presented
here only as points of reference for thinking and
planning and as hypotheses yet to be put to the final
test’’ (Wilson, 1959).
Like any good scientist, Wilson revised his
‘‘hypotheses’’ as more data became available, and the Principles
of Teratology matured as the field did. They were
discussed in a revised form in his 1973 monograph Environment
and Birth Defects (Wilson, 1973), but the definitive
version, which many of us have used in our teaching ever
since, appeared in 1977 in Wilson and Fraser’s magisterial
four-volume Handbook of Teratology (Table 3).
At a distance of more than 30 years, there are two
ways we could look at the Principles presented in Table
3: We could be very impressed at how well Wilson
understood teratology in 1977 (Wilson, 1977) and gratified
that almost all of the research done since then supports
the ideas he put forward at that time. Alternatively,
we could be disappointed that our understanding of teratology
has not changed very much over the last genera-
tion.
I prefer the former interpretation because the latter
overlooks a subtle but profound difference in our understanding
of Wilson’s third principle: Although we can
agree with Wilson that the chief manifestations of teratogenesis
observed at the level of the whole organism are
death, malformation, growth retardation, and functional
disorder, our knowledge regarding the mechanisms that
produce these abnormalities in response to a teratogenic
exposure has improved dramatically.
Wilson used the term ‘‘mechanisms’’ in a very specific
manner to mean the earliest, if not the first, event in the
pathogenic pathway between a cause (in this instance,
the teratogenic exposure) and its effect. He explained
that later events in the pathogenic process might be
expressed as one or more of a few higher-level effects.
He listed excessive or reduced cell death, abnormal cellular
interactions, reduced biosynthesis of important products,
aberrant morphogenic movement, and mechanical
disruption of tissues as examples, and suggested that
*Correspondence to: J. M. Friedman, Medical Genetics Research Unit, Box
153, Children’s & Women’s Hospital, 4500 Oak Street, Vancouver, British Columbia
V6H 3N1, Canada. E-mail: frid@interchange.ubc.ca
Published online 12 Augsut 2010 in Wiley Online Library (wileyonlinelibrary.
com).
DOI: 10.1002/bdra.20697
Birth Defects Research (Part A): Clinical and Molecular Teratology 88:766–768 (2010)
Ó 2010 Wiley-Liss, Inc. Birth Defects Research (Part A) 88:766À768 (2010)
these higher-level effects might, in turn, result in a few
final common pathways of abnormal development.
Wilson explicitly recognized that little was then known
about the earliest teratogenic mechanisms, and he
pointed out that, because they operated at the molecular
level, they were difficult or impossible to study experimentally
with the techniques available at that time
(Wilson, 1977). Nevertheless, he stressed the fundamental
importance of these primary developmental mechanisms
and devoted extended discussions to them in his later
presentations of the Principles of Teratology (Wilson,
1973, 1977).
Table 4 lists nine early mechanisms of teratogenesis
that Wilson discussed in the Handbook of Teratology. One
is immediately struck by the absence from this list of several
mechanisms that have been intensively studied over
the past few years and are now known to be important
in embryonic development. These include the following:
 Epigenetic control of gene expression (Corry et al.,
2009; Hemberger et al., 2009; Shi and Wu, 2009; Geiman
and Muegge, 2010)
 The effects of small regulatory RNAs (Lee et al.,
2006; Amaral and Mattick, 2008; Stefani and Slack, 2008)
 The imbalance of gene products resulting from submicroscopic
alterations of genomic structure such as copy
number changes (Zhang et al., 2009; Carvalho et al. 2010)
 Alterations of the cytoskeleton (Li and Gundersen,
2008; Johnson, 2009)
 Perturbations of the extracellular matrix (Holmbeck
and Szabova, 2006; Daley et al., 2008)
 Effects of mechanical forces on embryogenesis (Patwari
and Lee, 2008; Davidson et al., 2009; Nelson, 2009)
 Disturbances of intracellular or intercellular signaling
(Kovacic and Pozos, 2006; Arnold and Robertson, 2009;
Zeller et al., 2009)
 Dysfunction of molecular chaperones (Akerfelt et al.,
2007; Ni and Lee, 2007)
 Effects on the distribution of molecules into subcellular
compartments (Olkkonen and Ikonen, 2006; Gissen
and Maher, 2007) and
 Alterations of the integrity of intracellular organelles
(Steinberg et al., 2006; Zeviani and Carelli, 2007; Thoms et al.,
2009).
Table 1
The National Foundation Conference on Congenital Malformations as reported in the Journal of Chronic Diseases
10(2):83À151, 1959
Thomas M. Rivers:a
Introduction to the National Foundation Conference on Congenital Malformations
Josef Warkany: Congenital Malformations in the Past
F. Clarke Fraser: Causes of Congenital Malformations in Human Beings
James G. Wilson: Experimental Studies on Congenital Malformations
Donald D. Matson: Surgical Treatment of Birth Defects Involving the Central Nervous System
Rustin McIntosh:b
The Problem of Congenital Malformations: General Consideration
a
Dr. Thomas Rivers was a distinguished microbiologist who, as chairman of the National Foundation’s Committee on Research, oversaw
clinical trials of the Salk vaccine.
b
Dr. Rustin McIntosh was the Carpentier Professor of Pediatrics at Columbia University and Director of the Pediatrics Service at
Babies Hospital in New York City from 1931 to 1960.
Table 2
The Original (1959) Formulation of Wilson’s Principles
of Teratology (Wilson, 1959)
1. The susceptibility of an embryo depends
upon the developmental stage at which
an agent is applied.
2. Each teratogenic agent acts in a specific way
on a particular aspect of cellular metabolism.
3. The genotype influences to a greater or lesser
degree an animal’s reaction to a teratogenic agent.
4. An agent capable of causing malformations
also causes an increase in embryonic mortality.
5. A teratogenic agent need not be deleterious to
the maternal organism.
Table 3
Wilson’s Six Principles of Teratology as Presented in
the Wilson and Fraser Handbook of Teratology
(Wilson, 1977)
1. Susceptibility to teratogenesis depends on the
genotype of the conceptus and the manner in which
this interacts with environmental factors.
2. Susceptibility to teratogenic agents varies with the
developmental stage at the time of exposure.
3. Teratogenic agents act in specific ways (mechanisms)
on developing cells and tissues to initiate abnormal
embryogenesis (pathogenesis).
4. The final manifestations of abnormal development are
death, malformation, growth retardation, and
functional disorder.
5. The access of adverse environmental influences to
developing tissues depends on the nature of the
influences (agent).
6. Manifestations of deviant development increase in degree
as dosage increases from the no-effect to the totally
lethal level.
Table 4
Mechanisms of Teratogenesis as Presented in the
Wilson and Fraser Handbook of Teratology
(Wilson, 1977)
 Mutation
 Chromosomal nondisjunction and breaks
 Mitotic interference
 Altered nucleic acid integrity or function
 Lack of precursors and substrates needed for biosynthesis
 Altered energy sources
 Enzyme inhibitions
 Osmolar imbalance
 Altered membrane characteristics
767THE PRINCIPLES OF TERATOLOGY
Birth Defects Research (Part A) 88:766–768 (2010)
This list is not exhaustive, but it illustrates the breadth
of the advances that have been made in our molecular
understanding of teratogenic mechanisms since Wilson
emphasized the fundamental importance of these primary
developmental events. It also demonstrates the validity
of another concept that was implicit in the way
that Wilson, as an experimental teratologist, thought: the
idea that basic developmental mechanisms are shared
among species. The insight that teratology studies in one
species, such as mice, can inform our understanding of
developmental processes that occur in another species,
such as humans, has been critical to our progress
(National Research Council Committee on Developmental
Toxicology, 2000).
Wilson would have been pleased to learn that the
knowledge we have gained over the last 33 years has
strengthened the scientific basis for his Principles of Teratology
and that they remain central in our teaching of the
field that he helped to establish.
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