Researchers in Taiwan have found that first-degree relatives of individuals with myasthenia gravis have a higher risk of developing the disease. The risk is greater for patients’ siblings, the study found.
The study, “Familial aggregation of myasthenia gravis in affected families: a population-based study,” appeared in the journal Clinical Epidemiology.
While myasthenia gravis is thought to occur due to a combination of genetic and environmental factors, few studies have measured the contribution of genetic factors alone to disease susceptibility.
In this study, authors evaluated the familial aggregation and heritability of myasthenia gravis and the relative risks of other autoimmune diseases in the relatives of patients. They performed a population-based family study using the Taiwan National Health Insurance (NHI) Research Database.
From a population pool of 23.4 million people registered in the database, 15,066 had at least one first-degree relative with myasthenia gravis.
“We identified 8,638 parent–child relationships, 3,279 with an affected offspring, 3,134 with affected siblings, and 26 with affected twins,” the authors wrote.
The researchers measured the prevalence of myasthenia gravis and the relative risks of other autoimmune diseases in the relatives of affected patients. They also evaluated the contribution of heritability and environmental factors to disease susceptibility.
Their analysis showed that the prevalence of myasthenia gravis in the relatives of patients is 7.78-fold higher than in the general population. Among relatives, patients’ siblings had the highest prevalence, at 17.85.
Gender didn’t affect the relative risk of developing the disease: Male- and female-affected relatives had higher relative risks of 7.50 and 8.01, respectively.
Also, the risk for other autoimmune diseases in individuals with affected first-degree relatives is increased in individuals with affected first-degree relatives: 2.18 for systemic lupus erythematosus, 1.73 for primary Sjögren’s syndrome, 1.90 for autoimmune thyroid disease, and 1.68 for rheumatoid arthritis.
The authors estimate that the clinical heterogeneity associated with myasthenia gravis is mostly linked to familial transmission (82.1%) and, to a lesser extent, to nonshared environmental factors (17.9%).
Overall, “this nationwide family study confirms that an MG [myasthenia gravis] family history is associated with a high risk for the disease. Differential risk associated with different kinships suggests a strong genetic component in MG susceptibility. An MG family history also confers an elevated risk of other autoimmune diseases,” the authors wrote.
“Our findings may help improve the design of future familial and genetic MG risk studies and may also be useful in counselling families of patients with MG,” the study concluded.
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