Neuromyelitis optica spectrum disorder (NMOSD or NMO) is a rare inflammatory disease of the central nervous system (eye nerves, spinal cord, and brain). There is no cure for NMO. Symptoms of NMO are debilitating and can include blindness, muscle weakness, and paralysis.1
We want to answer the questions you might have about who gets NMOSD – are some people more likely to develop NMO? What role do genes, gender, and age play in determining risk of disease?
AQP4 and MOG antibodies
Antibodies are chemicals the immune system makes to kill germs. In some diseases, antibodies can also be harmful. The antibody that targets the protein aquaporin-4 (AQP4) leads to inflammation in NMO. AQP4 is found in brain cells called astrocytes and helps control water balance in the brain. The brain, spinal cord, and eye nerve (optic nerve) have AQP4. By attacking AQP4, AQP4 antibodies (AQP4-IgG) damage the protective coating (myelin) of the brain cells and lead to more inflammation. This causes the cycle of inflammation, antibody damage, and brain cell damage to continue.1-3
While many people with NMO test positive for AQP4 antibodies (AQP4-IgG), about 1 in 4 do not. Some test positive for antibodies that target myelin oligodendrocyte glycoprotein (MOG). Others test negative for both antibodies. This makes it harder for doctors to understand how some people get NMO and others do not.3
MOG antibodies (MOG-IgG) are believed to cause optic nerve or spinal cord attacks in MOG antibody (MOG-IgG) NMO that are similar to those of AQP4 antibody (AQP4-IgG) NMO. However, symptoms of this condition develop differently and need to be treated differently from those of AQP4 antibody (AQP4-IgG) NMO. Men and women are equally likely to get MOG antibody (MOG-IgG) NMO. Children have this disease more often than they have AQP4 antibody (AQP4-IgG) NMO.2-4
It is possible that MOG antibody (MOG-IgG) NMO and AQP4 antibody (AQP4-IgG) NMO will eventually be considered separate diseases, though this is debated. For now, they are considered subtypes of NMO.2,4
Doctors found that about 1 in 4 people with NMO do not have the AQP4 antibody (AQP4-IgG). Some of these people test positive for the MOG antibody (MOG-IgG). Others may not have either antibody. This adds to the complex nature of diagnosing and treating the disease.2-4
Ethnicity and race
The disease affects about 1 to 10 people per 100,000 worldwide. Although NMO is found everywhere, some locations have higher rates of disease. This is due to higher numbers of some ethnic groups. Higher rates of NMO have been found in people of African or Asian descent.1
A 2018 study published by the American Academy of Neurology included 427 people with NMO. The average time from diagnosis to death was almost 7 years. Those of African descent made up only 40 percent of the testing group but were 90 percent of those who died. The reasons behind this difference by race are not known at this time.5
Gender
Nearly 80 percent of those with autoimmune disorders are women. Women are diagnosed with AQP4 antibody (AQP4-IgG) NMO 9 times more often than men. Doctors think women get NMO more than men do because of changes in women’s hormones over time. Pregnancy causes even more changes to hormone levels. It is still unclear if pregnancy-related hormone changes impact who gets NMO. More studies are needed to determine why women get NMO more often than men.6-8
Age
NMO can occur at any age, but the average age of onset is between 40 and 50. Fewer than 5 percent of those with NMO are under the age of 18. Children are more likely to have optic neuritis (inflammation of the nerve bundles in the eye) at the onset of the disease. They are also more likely than adults to have a single NMO attack.9,10
Genes
Fewer than 5 percent of those with NMO have a relative who has also been diagnosed with the disease. This means it is not considered to be passed down from family.2,4
Changes to the structure or job of some genes may be a reason why NMO develops. These changes may be there from birth or could develop over time. Doctors are looking at how genes factor into the development of NMO.4
Comorbidities
Doctors use the term comorbidity to describe a condition that occurs at the same time as another condition. Comorbid illnesses can interact in ways that make both worse. Morbidity should not be confused with mortality. Morbidity means disease or illness. Mortality means death.
High blood pressure (hypertension) occurs most often in those with NMO. High blood pressure is common among all adults, which may be why it occurs often with NMO. Disease involvement of the part of the brain that helps control the heart may also lead to problems with blood pressure in some people. More studies need to be performed since existing ones have been too limited in number to prove a causal relationship.11,12
More than 1 in 3 people with AQP4 antibody (AQP4-IgG) NMO also has another autoimmune disease, including:13
- Lupus
- Sjogren’s syndrome
- Thyroid disease
- Myasthenia gravis
