This paper presents a sociological examination of the role of genetic counselors as advocates, not only for patients and their families, but also for genetic conditions themselves. In becoming activists for new disorders, genetic counselors are helping to create new categories that will shape expectations and treatment regimens for both existing patients and those who are yet to be diagnosed. By virtue of their expertise and their position at the intersection of several key professions and constituencies, genetic counselors are likely to play a central role in the way the genetic testing technologies, and especially 'genotype-first' diagnosis, impacts the way we understand and categorize developmental difference. I outline some of the promises and dangers that this kind of activism holds for people with developmental disabilities, and particularly the challenge presented by systemic ascertainment bias in the face of genotype-phenotype uncertainty. I argue that new testing techniques like microarray analysis that do not need to be targeted on the basis of clinical presentation throw these challenges into sharp relief, and that the genetic counseling community should consider how to marry advocacy for new genetic conditions with an emphasis on the indeterminate developmental potential of every child.