1. Prenatal Diagnosis Service, Women's Centre, Level 2, Oxford Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
2. WANDA, Wessex Genetics Service, Southampton, UK
3. Department of Human Genetics, University of Groningen, Ant. Deuslinglaan 4, NL-9713 AW Groningen, the Netherlands
4. Genetica Clinica & Epidemiologica, Dip Pediatra, Via Giustiani 3, I-35128 Padova, Italy
5. RACAV, Clinica Materno-Infantil, Hospital de Cruces, E-48903 Baracaldo (Vizcaya), Spain
6. GGD Rotterdam, Postbus 70032, 3000 LP Rotterdam, the Netherlands
7. Service de Genetique Medicale, Hopital de Hautepierre, Ave Moliere, 67098 Strasbourg Cedex, France