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the disease, risk factors characterize a certain group of individuals (e.g., siblings of
children with ASD who are at genetically higher risk to develop ASD), some of
whom will develop the prodrome and/or the disease and some who will not.
Vulnerability characterizes the affected individuals within the group at risk (i.e., only
those siblings who indeed develop ASD). Although we would like to be able to
identify all affected individuals with a certain vulnerability and delineate the
emergence of the prodrome of the disease/disorder, typically it is easier to identify the
general risk factor/s rather than the specific vulnerability. This results in the
identification of a larger group of at-risk individuals of whom later on, at some time in
the future, a smaller subgroup will, or will not, reveal the prodrome and/or the
disease/disorder. Early markers which define risk might not be precursors or part of
the prodrome or the disease; yet the prodrome of any given disorder, in its most
narrow interpretation, implies identification of the early symptoms of the disease. Yet
in the field of ASDs, as with other disorders and diseases as well, we are more
advanced in defining risks factors as possible precursors rather than a specific clinical
picture of a prodrome which most often than not leads to the disease.
As Rutter (1993), Werner and Smith (1982), and others have shown risk
factors may be genetic or due to biological, family and/or social environmental factors
and processes that affect the course of development. Risk factors may operate
independently or interactively in that genetic susceptibility may interact with certain
environmental factors and thus increase the risk for a certain disease. Furthermore, a
prodrome for a certain disease needs to be as specific and universal as possible for it
to be of clinical utility (for example; to initiate a preventative intervention).
Specificity requires that it is only present in the specific class of diseases/disorders,
ASDs in our case. Universality requires that all, or almost all, individuals who