Involvement of human muscle acetylcholine receptor alpha-subunit gene (CHRNA) in susceptibility to myasthenia gravis.

The muscle acetylcholine receptor is the major target of the autoimmune response in generalized myasthenia gravis. To investigate the role of the gene encoding the alpha subunit of the receptor (CHRNA), two stable polymorphic d[(GT).(CA)]dinucleotide repeats, designated HB and BB, were characterized within the first intron of CHRNA. The HB14 allele conferred a relative risk for myasthenia gravis of 2.5 in 81 unrelated patients compared with 100 control subjects. Very significantly, family analysis based on haplotype segregation data indicated that parental haplotypes associated with HB14 always segregated to the child with myasthenia gravis (P < 0.0002 for the comparison with the transmission of haplotypes not bearing HB*14), whereas their transmission to unaffected siblings was equilibrated. Myasthenia gravis patients also showed a high frequency of microsatellite variants unseen in controls. These findings implicate the CHRNA in susceptibility to myasthenia gravis.