There are chromosomal aberrations, to be sure. XXY, XYY, XXX (yes, for real), and others. Together they comprise between 0.5 and 1 percent of live births. Most fetuses with chromosomal abnormalities don’t survive gestation.
There is also a very rare possibility of an XY identical twin split that results in one child missing the Y chromosome and having only one X. That girl will have Turner’s syndrome. I also remember reading about a similar situation where a boy will have only a Y chromosome and no X, but I can’t remember what causes it. In either case, the children can develop more or less normally, but usually need hormone supplements to reach full maturity.