[1] Wayne State Univ, Sch Med, Detroit, MI USA
[2] Univ Med Ctr, Utrecht, Netherlands
[3] Johns Hopkins Univ, Baltimore, MD USA
[4] Hop La Pitie Salpetriere, Ctr Reference Malad Neuromusculaires Rares Paris, Paris, France
[5] Univ Milan, Milan, Italy
[6] Natl Hosp Neurol & Neurosurg, London WC1N 3BG, England