P-1. Juvenile myasthenia gravis: genetic aspects.

We report a 13-year-old boy developed diplopia and ptosis; diagnostic tests confirmed ocular myasthenia. Myasthenia gravis (MG) is a rare autoimmune disease characterized by production of antibodies to acetylcholine receptor at the motor end-plate responsible for impairment of neuromuscular transmission. The most important elements of diagnosis are clinical history and examination findings of fluctuating and fatigable weakness, particularly involving extraocular and bulbar muscles. Pediatric MG is very rare. MG results from the loss of tolerance to self-antigens. Thymic hyperplasia is observed in about 65% of MG patients, and thymomas are present in about 10%. MG can be classified according to the age of onset, presence or absence of anti-AchR antibodies. MG is a multifactorial disease, markedly influenced by genetic factors. The clinically typical form of autoimmune MG with thymus hyperplasia shows the most reproducible genetic associations, especially with the A1-B8-DR3 haplotype of the Major Histocompatibility Complex. The currently predominant working hypothesis assumes that they are mostly common single nucleotide polymorphisms. Among the genetic factors investigated in MG, the MHC holds a unique place. Apart from the MHC, a number of MHC-unlinked loci have been also investigated. One of them, the CHRNA1 locus, is of special interest, as it encodes the alpha subunit of the AChR. As with other autoimmune diseases, genetic predisposition to MG probably involves multiple genes. The precise contribution of the gene to human autoimmunity is not completely resolved. Which is the causative variant and how the expression of the gene is altered remain open questions.