Myasthenia gravis causes, after physical exertion, fatigability of the striated muscles, sometimes only of the eye (ptosis and diplopia). The results found, in the majority of patients, autoantibodies directed against the neuromuscular junction, for example anti-RACh and anti-MuSK, which are the most commonly found. Their absence (double seronegative myasthenia gravis) complicates the diagnosis.
An indicator of strong presumption
In search of a reliable and easy-to-access biomarker, an Israeli team measured the serum concentration of the free light chains (FLC) kappa (κ) and lambda (λ) in 73 people with auto-myasthenia gravis. immune and 49 healthy control subjects. Of the 73 patients, 20 were negative for anti-RACh and anti-MuSK (double seronegative), 53 positive for anti-RACh, 24 had an ocular form and 45 a generalized form of the disease.
According to the results of this study:
- there is a significant increase in the serum level of FLC κ, but not of FLC λ, in the group with myasthenia gravis in comparison with the control group, independent of the age of onset of the disease, of its manifestations (ocular or generalized form ) and the treatments received;
- the increase in the rate of FLC κ is found in double seronegative patients;
- the specificity of a FLC level κ ≥25 mg / L reaches 98% and its sensitivity 45% in double seronegative patients and those with an ocular form of myasthenia gravis.
The rate of FLC κ could therefore serve as a biomarker of the disease, in particular in cases of seronegativity and ocular form, alongside other arguments (history, clinical data, etc.). On the other hand, it cannot constitute a diagnostic test since other pathologies, in particular autoimmune, are also accompanied by an increase in the serum level of κ FLC.