Cluster of interconnected symptoms<\/p>\n
ME affects many body systems and produces a wide range of symptoms, including muscle pain and weakness, cognitive difficulties (often described as \u201cbrain fog\u201d), autonomic disorders such as digestive problems, postural hypotension and sleep disturbances.<\/p>\n
But the defining symptom of ME is post-exertional malaise, a state in which minor exertion\u2014physical, mental or emotional\u2014precipitates a significant worsening of symptoms that can last for hours, days or even weeks.<\/p>\n
One of the greatest challenges in studying ME is the heterogeneity of triggers, symptom clusters and disease progression.\u00a0<\/p>\n
\u201cME is not a single disease but rather a spectrum comprising several subgroups,\u201d said Moreau.<\/p>\n
\u201cAccurate diagnosis is difficult because ME and fibromyalgia present with very similar symptoms that can fluctuate over time. Our molecular analyses have shown that up to 40 per cent of individuals diagnosed with ME are in fact suffering from fibromyalgia\u2014and it\u2019s possible to have both conditions at the same time.\u201d<\/p>\n
Long COVID and epigenetics<\/p>\n
In about 75 per cent of cases, ME develops after a viral infection. Common triggers include the Epstein-Barr virus (mononucleosis), the influenza virus (the flu), West Nile virus, chikungunya, Zika and, more recently, SARS-CoV-2 (COVID-19).<\/p>\n
\u201cLong COVID is a good example,\u201d said Moreau. \u201cIt isn\u2019t an entirely new disease but more an intersection of various post-infectious pathways. Among those with the most persistent and severe symptoms, a significant proportion eventually meet the criteria for ME.<\/p>\n
“In other words, with COVID-19, medicine is rediscovering a condition already known to follow other infections, such as mononucleosis or the flu. It\u2019s surprising that so many people think long Covid is a new disease. Actually, it\u2019s just another post-infectious syndrome similar to conditions such as Lyme disease.\u201d<\/p>\n
Despite considerable effort, genetic research has yet to identify a clear cause of ME. Genetic variations explain only a small fraction of \u201csporadic\u201d cases, although some families are clearly more genetically predisposed than others.\u00a0<\/p>\n