Polydactyly happens before a baby is born. When a baby's hands and feet are first forming, they're shaped like mittens. Then the fingers or toes form. If an extra finger or toe forms, this causes polydactyly.

Is polydactyly a birth defect?

Polydactyly is a condition in which a person has more than five fingers per hand or five toes per foot. It is the most common birth defect of the hand and foot. Polydactyly can occur as an isolated finding such that the person has no other physical anomalies or intellectual impairment.

Is polydactyly caused by inbreeding?

Inbreeding would increase the percentage of polydactyl offspring, but there will always be a few normal-toed kittens in the litter, because of that recessive gene.