[1] Univ Groningen, Dept Med Genet, NL-9713 AW Groningen, Netherlands
[2] Univ Toronto, Hosp Sick Children, Toronto, ON M5G 1X8, Canada
[3] Osaka Univ, Sch Med, Biomed Res Ctr, Suita, Osaka 565, Japan
[4] Childrens Hosp Philadelphia, Philadelphia, PA 19104 USA
[5] Univ Penn, Philadelphia, PA 19104 USA
[6] Univ Toronto, Princess Margaret Hosp, Toronto, ON, Canada