What was the first genetic disorder identified?

Mmmmm. I'm going to differ from previous answers. In 1906 Sir Archibald Garrod delivered his treatise, Inborn Errors of Metabolism, to the Royal Society of Physicians as part of the Croonian Lectures. The first disorder he discovered (1902 and earlier) was alcaptonuria. He later expanded his work to include cystinuria, albinism, and pentosuria. He proposed the "one gene, one enzyme hypothesis."

Prior to that certain diseases like hemophilia were known to be hereditary, but mendelian inheritance had yet to be re-discovered.

Maybe it was something obvious like blindness or deafness. Since people have been giving birth since the beginning of time, I'm sure the first time someone noticed a genetic disorder they did not document it.

It depends on the disorder. There are 2 distinct reasons I would consider an abortion for that reason. If the unborn child would definitely die an extremely early death or if the child would definitely live in unbearable pain. Ethical is my number one reason. There is no acceptable religious reason. Forget social stigmas.

Sickle Cell Disease 1956.

red blood cells shaped like sickles instead of round flat disks. cant carry oxygen around the body efficiently, if at all

Sickle-Cell Disease in 1956