Fluorescence microsatellite analysis to study the parental origin of the supernumerary chromosome in Down's syndrome

Objective: Down's syndrome (DS) is an important cause of mental retardation. This study investigated the parental origin of the extra chromosome 21 in DS patients. Methods: Fourteen families each with a DS patient were recruited for analysis of nine microsatellite markers on chromosome 21. We collected DNA from both parents and the patient and used polymerase chain reaction to amplify nine segments on chromosome 21: D21S1435, D21S1436, D21S1437, D21S1446, D21S156, D21S258, D21S263, D21S265 and D21S270. One of each pair of DNA primers was labeled with a fluorescence dye. The amplified products were subjected to electrophoresis in a semi-automated DNA sequencer and then analyzed with Genescan software to determine the origin of the extra chromosome 21. Results: The extra chromosome 21 originated from the mother in 13 (93%) patients and from the father in one (7%) patient. Conclusions: Our findings were compatible with those from Caucasian patients. A great majority of Down's syndrome cases resulted from meiotic errors in the eggs.