Michael Yeaman, PhD: Let’s take a bigger picture of NMOSD [neuromyelitis optica spectrum disorder] for a moment. There has been a lot of evolution in this area over the past decade. Let’s talk a little about the global prevalence and incidence of NMOSD. There has been some interesting scientific and clinical research that begins to provide possible clues as to what may be the determinants that result in varying prevalence and incidence of NMOSD around the world. Michael, maybe I can start with you about the genetic, environmental, and cultural factors that may play a role in the varying prevalence and incidence around the world.
Michael Levy, MD, PhD: One of the interesting things we’ve noticed with the worldwide availability of the aquaporin-4 antibody is that the prevalence in all populations is remarkably similar. In Asia, North America and South America it is about 1 to 5 per 100,000 people. However, as a percentage of demyelinating disease, there is much more NMO [neuromyelitis optica] in non-Caucasian populations, such as in China, other eastern countries, and South America.
There is much more to multiple sclerosis [MS] in Caucasian countries, so the percentage of NMO in Caucasian countries is much lower, but the actual number per 100,000 is about the same, except for small pockets. For example, in Martinique, a far eastern Caribbean island, the prevalence is much higher – 10 per 100,000 – and 90% of the population is of African descent, and the entire island is on the national health care system, so the numbers they are very good. There is clearly a genetic component that we need to understand better. When you look at all predominantly Caucasian populations, such as in the United States and Europe, many of the patients in those countries who have NMO are non-Caucasian. In the United States, where African Americans make up about 13% of the total population, in the NMO population, they make up more than 40%, that is, they are 3 times represented in the United States.
Michael Yeaman, PhD: Thank you, Michael. This raises several important points. Perhaps we could ask Mitzi to comment a little further on the African American population in the United States. What are your thoughts on factors that may lead to a greater or disproportionate prevalence and incidence of NMOSD among African American or Black individuals?
Mitzi Williams, MD: It’s an excellent question. Of course, that being said, I believe genetics likely play a role. It is very interesting that now that we have better tools to identify NMOSD, it is causing us to re-examine many of our thoughts about MS phenotypes in the black population. Because traditionally, we thought of it as an opticospinal disease that affects the optic nerves and the spinal cord. But now many of us question whether we were really including people who had NMOSD in those early studies. Was this driving some of our descriptions of the MS phenotype in these populations?
It’s very interesting that it seems to disproportionately affect non-Caucasians. We are learning more about it in Africa in black populations. Most of the research that has come from those areas, which are very small, have described phenotypes that are much more typical of NMOSD than traditional MS. While it’s very interesting, it’s certainly raised more questions about re-examining how we’re looking at these populations in terms of MS and getting us back, not necessarily to the drawing board, but close to the drawing board, to ensured we are properly characterizing people with MS and not including some of those NMOSD populations that are likely to be misdiagnosed.
Michael Yeaman, PhD: Excellent points. Mirla, we know that Hispanic and Latino individuals may also be disproportionately affected not only in prevalence and incidence, but also in disease severity. Can you comment on this please?
Mirla Avila, MD: Yes, we lack studies to know exactly the numbers in the population of Latin America. I may be biased because I practice in Texas, but about 70% of my NMOSD patients are Hispanic. If you look at Central America and Mexico, we have a fairly high number of patients with NMOSD. That being said, throughout Latin America, there is a different set of genes from Europe and Africa, so it would be interesting to see from the Hispanic population who has more Caucasian or African genetics and if we still see that difference. That would be an interesting thing that has yet to be answered.
Michael Yeaman, PhD: Well said. And we know there’s a lot of unknowns in South America, and there’s a lot of work going on there, so all those points are well taken.
The transcript has been edited for clarity
