Early-Onset Cataracts Are a Signal to Consider a CTX Diagnosis
Robert Steiner, MD, clinical professor at the University of Wisconsin School of Medicine and Public Health, talks about the importance of implementing newborn screening to assess for CTX, as well as the ocular complications that are a hallmark of the condition.
Question:
Can you talk about genetic testing to detect cerebrotendinous xanthomatosis (CTX)?
Robert Steiner, MD:
CTX or cerebrotendinous xanthomatosis is a relatively rare genetic condition. It can be diagnosed either biochemically or by genetic testing. There are only a few labs in the country that can diagnose CTX biochemically, but it’s not a terribly difficult thing to do. But in some cases, the biochemical results either may not be available or may be borderline. In that case, it’s always a good idea to confirm the diagnosis with genetic testing. Genetic testing for CTX is now widely available. It’s essentially sequencing the gene that’s abnormal in the condition, and that gene sequencing is now readily available in a number of laboratories throughout the country.
Question:
What are the treatments available for CTX?
Robert Steiner, MD:
There is an excellent treatment for CTX currently available. It’s called chenodeoxycholic acid or CDCA. CDCA is an FDA-approved medication. Now it’s not FDA-approved for the purposes of treating CTX. It was originally approved for treating gallstones. It’s essentially never used anymore for treating gallstones; it’s really only used for treating CTX. But when prescribed for CTX, we are really using it off-label, again, because it’s not marketed for use in CTX. But it was developed in the late 1970s and early 1980s, and has been used ever since then very successfully. It’s a very safe medication to use in CTX. Very safe, very effective. One day we hope it will be actually approved for the specific purpose of treating CTX. Another medication that can be used, it may be especially useful in young infants with CTX, is cholic acid. Cholic acid is a different bile acid that has been studied a little bit in CTX, and it really is marketed for use in bile acid synthesis disorders, which CTX falls into. It really is marketed for CTX, but first-line therapy would be CDCA in most cases.
Question:
Early-onset cataracts are a common feature in patients presenting with CTX. Can you talk about the importance of educating physicians on this? How can physicians connect these cataracts with a potential CTX diagnosis?
Robert Steiner, MD:
There are many different causes of early-onset cataracts, and I’m talking about cataracts that occur in children, adolescents, and young adults, not senile cataracts as they’re called, that occur very commonly in older people related to aging. When cataracts occur in young people, especially when they’re bilateral and both eyes are affected, it’s very important for clinicians to look for CTX, because in CTX, cataracts are just one of the many complications. Individuals with CTX can develop difficulties walking and talking. They can develop early-onset dementia, and yet it’s a very treatable disorder. We can prevent those complications with proper treatment. There have been studies done looking at groups of individuals who have early-onset cataracts, and a significant percentage of those people have CTX. It’s one of the few disorders that affects more than just the eyes, causes more than just cataracts, but is also very treatable and serious if not treated.
Our recommendation is that ophthalmologists, when they see early-onset cataracts, especially bilateral, should think of CTX and test for it. If they aren’t able to test for it themselves, work with a clinician such as a genetic counselor or a clinical geneticist to provide that testing. Because CTX is treatable, and it’s so hard to diagnose because the complications are so varied and overlap with other more common disorders, we are advocating very strongly for introduction of newborn screening for CTX. There already is a way to screen all newborns for CTX. The methods have been developed, they’ve been tested; they work well. I and others in the field really feel very strongly that we should be implementing newborn screening in the United States and around the world to prevent the serious complications of CTX, which, again, can affect our ability to walk and talk and grow normally, and lead a normal life.
