What Role Does Heredity Play?

SAVANNAH, GEORGIA — One patient with autoimmune myasthenia gravis (MG) has a niece with the same diagnosis, and at least one of his other close relatives may have it too. Another patient with MG lost his father and brother to complications from the disease, while a surviving brother also has it. These two cases, reported at a meeting of nerve/muscle specialists, spotlight one of the mysteries of MG: What role does heredity play in this disorder?

“Clinical familial associations — when transmission appears to be vertical, from parent to offspring — suggest that there is much yet to learn about genetic bases for autoimmunity and how certain mutations could favor selection for specific immune disorders,” said Elena Shanina, MD, PhD, a neurology professor at The University of Texas Medical Branch, Galveston, Texas, in an interview. She and colleagues presented the two case reports at the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) 2024.

As Shanina noted, MG is usually sporadic without a link to heredity. However, she said, research suggests that up to 7% of patients have MG in their family history.

“There are well-described genetic causes for congenital myasthenic syndromes, in which mutations occur in genes for neuromuscular junction (NMJ) proteins affecting NMJ function. However, much less is known about genetic associations to autoimmune MG,” she said.

“More than a decade ago, differences in HLA DQ haplotype-associated presentation of AChR alpha-chain peptides were suggested to suffice in producing MG, and specific HLA DQ susceptibility links were found predisposing to MG. More recent studies have tried to identify specific genes such as CTLA4 mutations that enhance autoimmunity and neuroinflammation.”

In one of the case reports, a 75-year-old White man with hereditary coagulopathy presented with myasthenic crisis in the setting of acute pulmonary embolism. Chronic symptoms included diplopia, ptosis, and proximal muscle weakness.

A niece of the patient has been diagnosed with MG and suffers from ocular symptoms. Meanwhile, an uncle has ptosis but no diagnosis yet, and a daughter has dermatomyositis. Like MG, dermatomyositis is an autoimmune disease that causes muscle weakness.

The patient, who’s CTLA4 negative, is faring well on eculizumab after failing standard therapies, Shanina said.

In the other case, a 67-year-old Hispanic man presented with diplopia, generalized fatigue, and weakness. Like the other patient, he was seropositive for acetylcholine receptor antibodies.

This patient lost his father and brother to complications from MG. Another brother, who’s still living, also has MG.

“The patient has minimal manifestation status with disease and is currently controlled using oral immunomodulatory therapies,” Shanina said. “He is also CTLA4 negative.”

Shanina called for research exploring mutations and inheritance patterns in families with MG.

“If there are genetic causes that increase autoimmunity with specific propensity for certain immune diseases, correcting those mutations could fundamentally change how we treat — and prevent — at least some autoimmune diseases,” she said. “For example, if HLA linkage is directly involved in determining susceptibility to MG, and if the presence of a specific HLA locus allele is sufficient to produce disease, HLA gene editing could be a future therapy to prevent such diseases. Likewise, monoclonal antibodies that target products of genes that increase risk for autoimmunity might be able to reduce such risks without modifying the patient’s genome.”

Henry J. Kaminski, MD, professor of neurology at The George Washington University, Washington, DC, is familiar with the report’s findings. In an interview, he noted that while genetic profiles can make MG more likely, “the situation is not like Huntington’s or Alzheimer’s where there is a strong genetic risk.” 

Instead, he said, there’s “a genetic risk coupled to some environmental stimulus that leads to the development of MG, which is true for many complex autoimmune conditions.” 

While he doesn’t think the two new case reports are especially noteworthy, Kaminski said “the ability to assess genetic risk factors across patients will elucidate understanding of MG. Personalized medicine choices will likely require understanding of genetic risks.”

While understanding MG in families is “always good to know from a research perspective,” there’s no reason to launch surveillance of relatives to see if they also have the disease, he said.

Also, Kaminski cautioned that it’s important to differentiate autoimmune MG from congenital myasthenia, an even more rare genetic disorder of neuromuscular transmission. “Congenital myasthenias will not improve with immune therapy, and patients will suffer complications for no reason,” he said. “A patient who is seronegative should be assessed for congenital myasthenia with the right clinical presentation. The condition would be more likely in patients with a family history of symptoms similar to MG. It may be symptomatic at birth, but patients may present in adulthood.”

Kaminski noted that his team is collecting saliva samples from patients with MuSK-MG, a rare MG subtype linked to more severe cases, for genetic testing and genome-wide association studies.

There was no study funding, and the authors have no disclosures. Kaminski is principal investigator of arare disease network dedicated to MG.