Down Syndrome Abstract
of the Month:
July 1998
Anomalies in Down syndrome individuals in a large population-based registry
Torfs CP, Christianson RE
Am J Med Genet 1998 Jun 5;77(5):431-438
California Birth Defects Monitoring Program, Emeryville, CA, USA
Abstract:
In a population of close to 2.5 million infants born from 1983 to 1993 registered in the California Birth Defects Monitoring Program, we compared the prevalence of structural birth defects among 2,894 infants with Down syndrome (DS) with that of infants without DS. Among 61 defects uniformly ascertained in affected and unaffected infants, 45 were significantly more common in DS, with atrioventricular canal (risk ratio = 1,009), duodenal atresia (risk ratio = 265), and annular pancreas (risk ratio = 430) being the most common. Most defects of blastogenesis and most midline defects were either nonsignificantly associated or not observed in infants with DS. Theories on the pathogenesis of defects in trisomies must account for the lack of and for the presence of specific defects.
My comments:
Representing an amazing amount of work, this paper investigates births over the range of 1983 to 1993 in California as reported to the state's Birth Defect Monitoring Program. Not all counties in California are represented, but the state compiled records of 2,493,331 births in this period. 2,894 live births of babies with DS were recorded, making a ratio of 1 baby with DS in 861 total births. Still births were not counted for this study as it's hard to determine associated anomalies in babies that are stillborn. The paper gives a detailed report of how the statistics are gathered.The paper specifically did not count facial features associated with DS, nor were features counted that aren't usually reported to the Monitoring Program such as umbilical hernias.
The most common group of all anomalies were cardiac defects, at a rate of 108 times more common in DS than non-DS. The most common defect of all was the ventricular septal defect, at 1000 times more common in DS than non-DS. The paper gives the incidence of all cardiac defects found in these children.
Of the non-cardiac anomalies, the most common occurring in DS were duodenal atresia (blockage of a part of the small intestine) at 265-fold, Hirschsprung disease at 101-fold, and annular pancreas (shows up as chronic vomiting and/or pancreatitis) at 430-fold. The paper lists 17 other anomalies more common with DS than non-DS.
What was also interesting was what was _not_ associated with DS: specifically, "blastogenic defects." These are defects that occur due to abnormal development of the embryo at the time of closure of the neural tube. These defects include spina bifida, anencephaly, cojoined twins, intestinal duplication and a whole host of other mid-line body defects. The only such defects that did show up as associated with DS were holoprosencephaly, anal atresia, Tetrology of Fallot and tracheoesophageal fistula. One possible reason for this lack of association is that the combination of such a defect and trisomy 21 increases the risk of spontaneous miscarriage.
So why, besides getting some very nice statistics, is this data important? Because if the geneticists and molecular biologists are going to establish a connection between the overexpression of genes and the features of DS, the hypotheses of gene imbalance or additive gene effects will have to take into account the presence of absence of these anomalies.