What do you suggest if my grandchild is a week old and doctors have noticed he only has 1 crease on each hand what could it be?

Depends: What have the doctors told you? Are there any other physical findings they have mentioned ? Sometimes single hand creases can indicate a congenital disorder like Down's syndrome, sometimes it means nothing. I personally have single hand creases myself. I think I'm pretty normal.

It happens: This occurs at least on one side in roughly 7% of the population.It's origin is thought to reflect how baby holds its hand in the womb.There is an association with low muscle tone and as such it appears in some conditions where this is common like Down syndrome.I'd follow the doctors lead on this.If they express no particular concern I would look on it as nothing to lose sleep over.