title: Maternal Germinal Trisomy 21 in Down Syndrome.
abstract: It has now been over 50 years since it was discovered that Down syndrome is caused by an extra chromosome 21, i.e., trisomy 21. In the interim, it has become clear that in the majority of cases, the extra chromosome is inherited from the mother, and there is, in this respect, a strong maternal age effect. Numerous investigations have been devoted to clarifying the underlying mechanism, most recently suggesting that this situation is exceedingly complex, involving both biological and environmental factors. On the other hand, it has also been proposed that germinal trisomy 21 mosaicism, arising during the very early stages of maternal oogenesis with accumulation of trisomy 21 germ cells during subsequent development, may be the main predisposing factor. We present data here on the incidence of trisomy 21 mosaicism in a cohort of normal fetal ovarian samples, indicating that an accumulation of trisomy 21 germ cells does indeed take place during fetal oogenesis, i.e., from the first to the second trimester of pregnancy. We presume that this accumulation of trisomy 21 (T21) cells is caused by their delay in maturation and lagging behind the normal cells. We further presume that this trend continues during the third trimester of pregnancy and postnatally, up until ovulation, thereby explaining the maternal age effect in Down syndrome.
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm S-171 76, Sweden. hultenmaj@gmail.com.
authors.forename: Maj A
authors.initials: MA
authors.lastname: Hultén
authors.affiliation: Department of Neurobiology, Care Sciences and Society, KI Alzheimer Disease Research Center, Karolinska University Hospital, Huddinge, Stockholm S-141 86, Sweden. linnstedt@gmail.com.
authors.forename: Linn
authors.initials: L
authors.lastname: Öijerstedt
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm S-171 76, Sweden. erik.iwarsson@ki.se.|Department of Clinical Genetics, Karolinska University Hospital, Stockholm S-171 76, Sweden. erik.iwarsson@ki.se.
authors.forename: Erik
authors.initials: E
authors.lastname: Iwarsson
authors.affiliation: Department of Clinical and Experimental Medicine, Linköping University, LMC, University Hospital, Linköping S-581 85, Sweden. jon.jonasson@lio.se.
authors.forename: Jon
authors.initials: J
authors.lastname: Jonasson
keywords: Down syndrome; aneuploidy; germinal mosaicism; maternal origin; trisomy 21