1. Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, TX 77030 and Texas Birth Defects Research Center, Texas Birth Defects Monitoring Division, Texas Department of Health, Austin, TX 78756
2. March of Dimes Birth Defects Foundation, California Birth Defects Monitoring Program, Oakland, CA 94608
3. Division of Medical Genetics, Children's Hospital, Oakland, CA 94609