Ever since scientists first used CRISPR-Cas9 to edit living human cells in 2013, they’ve been saying that the possibilities for using it to treat disease are virtually endless.

In just the past few years, advances in CRISPR have been happening at a breakneck speed—and companies have sprung up to commercialize the technology. Now, patients in Europe and the U.S. could be treated with CRISPR-based therapies as soon as 2018.

The hope is that CRISPR could be used in a one-time procedure to cure some of the most devastating inherited disorders and cancers, some of which have no or few current treatment options. Scientists want to deploy the technology to fix genetic errors in a person’s DNA, getting at the root of disease.

That might be the dream, but the reality is far different. Already, investigators have delayed the start dates of clinical trials. And the studies slated to start in the next year or two will treat a small number of patients with a few rare diseases. It will probably be years before the technology can be used for more common diseases in more patients.

CRISPR Therapeutics, based in Cambridge, Massachusetts, became the first company to ask permission from European regulators to begin a trial next year. The company will use the gene-editing technology to fix a genetic defect in patients with beta thalassemia, an inherited blood disorder.

Samarth Kulkarni, CEO of CRISPR Therapeutics, says the company is also planning to request approval from the U.S. Food and Drug Administration in the first half of 2018 to begin a CRISPR trial for sickle-cell disease.

About 15,000 people in Europe have beta thalassemia, and around 100,000 in the U.S. have sickle-cell. Both are genetic disorders caused by mutations in the genes that make hemoglobin, an important protein in red blood cells that carries oxygen throughout the body. Typically, both parents must pass on an abnormal gene in order for a child to develop the disease.