Our 20 month old son was born with half of his index finger nail grown in and the other half is just a little dot. When he was born I asked our midwife what it could be and she said that the nail will grow together by his first birthday. His birthday passed and his nail doesn't seem to be fusing together at all. Each piece is still just growing on its own. We have had a few pediatricians so far and I have asked every one of them and they all said that it's nothing to worry about and the nail will eventually grow together.
We recently saw a naturopathic doctor and I asked her about the nail and she said that it looks like a mineral deficiency and once we give him a mineral supplement it should all grow together. Has anyone heard of this or know what it could be? We are going to try the minerals, but I am curious to see if anyone else has seen this before.
I have no idea what it is called but I was born with half a thumbnail and the other side just a piece like you are describing. Both of my thumbs are like that. Mine have never grown together and I'm middle-aged by now. I actually found your post because I'm looking for answers myself as to what caused this.