Polydactyly is a condition in which a person has more than the normal number of fingers or toes. It can occur in association with other physical anomalies or intellectual impairment, or it may occur as an isolated birth defect. Polydactyly can either be inherited or it can arise sporadically in an individual.
Polydactyly. In my human genetics class in college, I mentioned to my lab partner that I had never met anyone with polydactyly, and he replied, “Yes, you have.” It turns out that he was born with an extra finger on each hand that had been surgically removed, which helps to explain why I wouldn't have noticed. His hands actually looked nothing like the different photographs of hands with polydactyly that we had studied in class which had illustrated a lot of different ways that it can manifest with the extra fingers in different locations.
NHGRI Bioethics Core