Can Huntington disease ever be sporadic or is it always familial?

It depends. The classic Huntington disease causing genetic mutation is ALWAYS familial, BUT paternity is NOT always known or a parent may have died before the disease is manifest, so it may appear sporadic. There is a rare HD-like mutation that behaves just like classic HD, but represent a different abnormal area on the genome. This one is also not thought to arise sporadically and the same caveats apply.