¹Department of Genetics, Institute of Child Health, Athens, Greece.

²Department of Medical Genetics, The John F Kennedy Institute, Glostrup, Denmark.

³Mitera Maternity Hospital, Athens.

⁴Department of Neurology, Eginition Hospital, Athens, Greece.

⁵Institut für Humangenetik, Universitätsklinikum Essen, Essen, Germany.

⁶Department of Clinical Genetics, Uppsala University Children's Hospital, Uppsala.

⁷Department of Clinical Genetics, Karolinska Hospital, Stockholm, Sweden.

⁸Department of Pediatrics, Aarhus University Hospital, Aarhus, Denmark.

⁹Genetics Unit, Second Department of Pediatrics, 'Aglaia Kyriakou' Children's Hospital, Athens, Greece.

¹⁰Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark.

¹¹Department of Medical Genetics, Haukeland University Hospital, Bergen, Norway.

¹²Department of Medical Genetics II, University Hospital Motol, Prague, Czech Republic.

¹³Clinique de Pédiatrie et Génétique Médicale, Groupe Hospitalier Pellegrin-Enfants, Bordeaux, France.

¹⁴Abteilung Humangenetik, Medizinische Hochschule Hannover, Hannover, Germany.

¹⁵Centre de Génétique Médicale, Hôpital d'Enfants de la Timone, Marseille, France.

¹⁶Sección Genética Clínica, Hospital 'La Paz', Madrid, Spain.

¹⁷Department of Cytogenetics, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus.

¹⁸Service d'Histo-Embryologie et de Cytogénétique, Hôpital Necker Enfants-Malades, Paris, France.

¹⁹Institut für Humangenetik, Zentrum für Hygiene und Humangenetik der Universität Göttingen, Göttingen, Germany.

^aCorrespondence: Dr Michael B Petersen, Department of Genetics, Institute of Child Health, 'Aghia Sophia' Children's Hospital, GR-11527 Athens, Greece. Tel: (30) 1 77 53 030; Fax: (30) 1 77 00 111.

Causes of chromosomal nondisjunction is one of the remaining unanswered questions in human genetics. In order to increase our understanding of the mechanisms underlying nondisjunction we have performed a molecular study on trisomy 8 and trisomy 8 mosaicism. We report the results on analyses of 26 probands (and parents) using 19 microsatellite DNA markers mapping along the length of chromosome 8. The 26 cases represented 20 live births, four spontaneous abortions, and two prenatal diagnoses (CVS). The results of the nondisjunction studies show that 20 cases (13 maternal, 7 paternal) were probably due to mitotic (postzygotic) duplication as reduction to homozygosity of all informative markers was observed and as no third allele was ever detected. Only two cases from spontaneous abortions were due to maternal meiotic nondisjunction. In four cases we were not able to detect the extra chromosome due to a low level of mosaicism. These results are in contrast to the common autosomal trisomies (including mosaics), where the majority of cases are due to errors in maternal meiosis.

trisomy 8; mosaicism; nondisjunction; Warkany syndrome; microsatellites; mitosis; meiosis