The inspiration for this post is from a cat I met while shadowing at a Veterinary Hospital. I believe she was a Maine Coon and the poor thing came in with an extra digit on each of her front paws. The bad part wasn’t the digits, but the ingrown nails between them. Oddly enough, the nails had no pad associated with them so they were just growing from the webbing. The right paw was the worst with the actual ingrown nail (and a possible infection) and the left paw’s randomly sprouted nail had grown to spiral like a ram horn. However, the nails are beside the point. I’ve always been intrigued by diseases, especially ones that can result in something sprouting an extra limb, so I figure why not dive into the matter of polydactyly, also known as supernumerary digits.
As you might have guessed, polydactyly is a condition where an animal has extra fingers or toes. The extra digit may be fleshy, contain bones, or even be fully functioning. The postaxial manifestation (on the side of the little finger) is most common, followed by preaxial (by the thumb) and then central (the middle three fingers). The new digit may jut from an existing, normal digit, or (when associated with the hand) from the wrist as do the other digits. The condition is a congenital anomaly, meaning it exists at or before birth.
- Asphyxiating thoracic dystrophy
- Carpenter syndrome
- Ellis-van Creveld syndrome (chondroectodermal dysplasia)
- Familial polydactyly
- Laurence-Moon-Biedl syndrome
- Rubinstein-Taybi syndrome
- Smith-Lemli-Opitz syndrome
- Trisomy 13
While supernumerary digits may be associated with one of the preceding syndromes, or perhaps some even unlisted, it can also occur on its own. According to NIH, African-Americans, such as myself, are more prone to inheriting a 6th digit than other ethnic groups, which in most cases is not associated with a genetic disease. When occurring by itself, polydactyly might be due to an autosomal dominant mutation in a single gene.
Here’s a very short video. Very briefly, you can see the supernumerary digit.