New research reveals that race and ethnicity significantly influence how myasthenia gravis (MG) manifests in U.S. patients, with African American and Hispanic individuals developing the autoimmune condition at much younger ages and experiencing more severe initial symptoms.

The study, drawing from two large national databases, highlights a stark divide in disease onset. While white patients typically show symptoms in their 50s, African American patients often face the disease in their mid-30s.

The analysis found that MG patients who are African American or Hispanic are usually much younger at the time of disease onset compared with white and non-Hispanic patients. Data also indicated that MG patients who are African American or Indigenous tend to have more severe disease at onset than white or Asian patients. Rates of co-occurring cancer diagnoses also varied across racial and ethnic groups.

“Our analysis … concludes that age at onset, baseline [disease severity] scores, onset symptoms, and comorbid cancer frequency varied between racial and ethnic groups,” researchers wrote.

The study, “Variations in clinical features and disease burden of myasthenia gravis between racial and ethnic groups: A retrospective cohort study of two national databases,” was published in the Journal of the Neurological Sciences. 

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Disparities in onset and severity

MG is an autoimmune disease driven by self-reactive antibodies that disrupt the communication between nerve and muscle cells, resulting in symptoms of muscle weakness and fatigue.

The disease can affect people of any racial or ethnic background, but several studies have shown that, in the U.S., disease manifestations tend to vary across different racial/ethnic groups. However, most of these studies were relatively small in scale.

To address this issue with a larger sample size, scientists in the new study compiled data from two large U.S. databases: the MG Foundation of America Global MG Patient Registry (MGFAPR) and the National Inpatient Sample (NIS).

The primary analysis included data on more than 3,000 patients in MGFAPR. Specifically, there were 3,099 patients identified as white, 178 African American, 47 Asian, and 151 Indigenous. Ethnicity data were available from 188 patients who identified as Hispanic and 3,431 who identified as non-Hispanic.

The researchers noted that socioeconomic factors varied considerably across these groups. For example, patients who were white or Asian generally had higher household incomes than those who were Indigenous or African American.

The study also found that the average age at symptom onset varied substantially by race, with earlier onset in non-white groups. About 84% of African American patients had early-onset MG, defined as symptom onset before age 50. Rates of early-onset MG were also higher among Asian (79%) and Indigenous (52%) patients, compared with white patients (41%). A similar difference in rates of early-onset disease was also found comparing Hispanic and non-Hispanic patients (62% vs. 44%).

In addition to age, patterns of symptoms at onset also varied across racial groups. About two-thirds of patients who were African American or Indigenous reported limb weakness at onset, whereas less than half of white and Asian patients had limb weakness when the disease first manifested.

Scores on standardized measures of disease severity generally reflected more severe disease at onset in Indigenous and African American patients compared with white patients. Asian patients, meanwhile, tended to have lower scores than white patients.

Hospitalization and co-occurring conditions

Rates of co-occurring disease also differed by race. For example, more than 20% of white MG patients had a co-occurring diagnosis of cancer, compared with less than 5% of African American patients. This can at least partially be explained by the fact that white MG patients tended to be older at the time of MG onset, according to the researchers.

Analyses from the NIS database, which tracks hospitalization records, also showed differences by race and ethnicity. Compared with white patients, African American and Hispanic patients were more likely to require a ventilator while in the hospital and tended to have higher hospitalization-related costs. However, rates of in-hospital mortality were higher among white patients.

Again, the researchers noted that these differences are likely related to the fact that white patients tend to be older when they develop MG. However, this raises the question: why are white patients on average so much older than patients of other races at MG onset? The researchers aren’t entirely sure, highlighting a need for further study to better understand how race and ethnicity affect MG.