• Question: how do people grow extra finger or limbs while they forming?

    Asked by gabby1996 to Carol, Ellie, John, Philip, Rebecca on 26 Jun 2012.
    • Photo: Rebecca Lacey

      Rebecca Lacey answered on 26 Jun 2012:

      The medical name for being born with extra fingers or toes is “polydactyly”.

      During development in the womb a chemical is released by an area of the hand or foot close to where the largest digit will form – ie the big toe or thumb. There is a gradient of this chemical across the limb. In the area with the highest concentration of the chemical the thumb or big toe forms. In the area with the lowest concentration of this chemical the smallest finger or toe forms. This chemical is called Sonic Hedgehog (SHH) – no, really!!

      In some people this gradient is changed causing loss or gain of digits. This might be caused by a physical block preventing SHH from distributing across the limb or an increase/decrease of SHH being released.

      Research has been done with species where limbs can be grown in adulthood, e.g. a salamander (if you cut off a limb of an adult salamander it will grow back again!) The potential for growth of limbs in humans is obvious and a potential goal for the future.

    • Photo: Carol White

      Carol White answered on 2 Jul 2012:

      Wow, I think that’s really cool that one day we might be able to use the Sonic Hedgehog chemical to grow new limbs! Gabby1996 & Rebecca, between you, you’ve taught me something new there!

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