Polydactyly

Polydactyly is a birth defect in which a person is born with extra fingers or toes, popularly called a sixth finger. The hands are affected more often than the feet. The extra digit can be painful, can cause clumsiness and can affect how a person feels about their appearance. It is linked to at least 39 genetic mutations and may occur by itself or together with other defects, and it often runs in families. The underlying mechanism is an error in the formation of the limb bud early in development. It can be seen before birth on ultrasound as early as nine weeks, and X-rays can help once a child is older than a year. Treatment ranges from removal by cautery to more involved surgery, commonly around the age of two. It affects roughly 4 to 12 of every 10,000 newborns and is the most common defect of the hands and feet. Its opposite is oligodactyly, fewer digits than usual.