In the wake of the 2017 American Society of Hematology Meeting and Exposition, many medical professionals are keeping a sharp eye on two companies looking to change how diseases such as hemophilia are treated.

During the meeting, Spark Therapeutics released data on its experimental gene therapy treatments meant to help patients better manage hemophilia. Beyond this disease, gene therapy has become a hot topic of conversation for its potential to treat diseases that otherwise require constant therapy over the course of a lifetime.

The two primary challenges for creating viable gene therapy practices are finding a suitable vector and type of cells for genetic material. The general idea behind it is to replace mutated genes with healthy versions—for instance, tackling the genes that make diabetics unable to produce insulin. However, technical concerns such as targeting the proper cells and ensuring that the body can properly regulate the new genes have preventing these treatments from becoming widespread.

Spark’s hemophilia treatment has proven to consistently reduce bleeding among patients. However, results showed that levels of factor VIII, a protein essential for blood clotting, were still fairly low. This has lead to backlash against Spark from investors and the company admitting that “further optimization” is needed. Spark expressed concern over factor VIII levels, mentioning its desire to better regulate the protein and ensure that patients receive the proper dose of therapy. Excessive levels of factor VIII can lead to blood clots and potentially present new problems for patients.

Perhaps more promising were results released by BioMarin, another biotechnology firm with an interest in gene therapy. The company studied nine patients, finding that their therapy treatments increased factor VIII levels to at least 50% of normal, a drastic improvement for those suffering from hemophilia.

However, Spark is not deterred, and is working to test new doses on patients in the coming months while BioMarin works to gain approval for distributing its treatments more widely. Both are focused on hemophilia A, the most common form of disease, but are developing treatments for other forms as well.

Other firms are working to address other diseases that stem from a single genetic defect. Immunodeficiency treatments are being examined as a possible cure for what is sometimes known as “bubble baby” disease. This debilitating condition, caused by severe immune system issues, drastically affects the lives of those affected by it, forcing them to live in isolation. While researchers don’t want to be optimistic just yet, they feel that they have made steps toward bringing victims back into society, with 6 of 7 infants now leading healthy lives.

In the future, it may be possible for gene therapy to help cure more complex genetic defects. For now, the biggest issue will be finding universal measures of treating these diseases—often, variations in a condition can render gene therapy useless. Still, the potential to permanently help patients who would otherwise require constant treatment is enough for biotech companies to try to stake their claim in this new market.