Chromosome Redundancy and Gene Expression: an Explanation for Trisomy Abnormalities

Congenital cardiovascular malformations associated with chromosome abnormalities: an epidemiologic study

The Baltimore-Washington Infant Study is a population-based case-control study that seeks to identify risk factors for cardiovascular malformations. Between 1981 and 1986, a total of 2102 infants with cardiovascular malformations were ascertained, among whom 271 (12.9%) also had a chromosome abnormality. Among 2328 random control subjects, only two had a chromosome abnormality. Down syndrome with cardiovascular malformations had a maternal age-adjusted regional prevalence of 4.33/10,000 for the white population and 3.70/10,000 for the nonwhite population. Endocardial cushion defect, the predominant cardiac abnormality in Down syndrome (60.1%), rarely occurred as an isolated cardiac lesion (2.8%). The absence of transpositions and the rarity of heterotaxias and of right- and left-sided obstructive lesions in trisomies indicate that there may be a genetic influence on specific embryologic mechanisms. Alimentary tract lesions were more common in Down syndrome than among euploid patients with heart disease and more severe than in control subjects. Urinary tract lesions also occurred in excess of the rate in control subjects. The coexistence of these major malformations with heart disease raises the possibility of incomplete expression of the VA(C)TER (vertebral, anal, cardiac, tracheal, esophageal renal) association. The selective association of chromosome abnormalities with certain cardiovascular defects is now beginning to be explained by reported embryologic studies on cellular characteristics. An explanation of the negative association with transposition and obstructive lesions requires further multidisciplinary studies on genetic and epigenetic factors.

Regulation of enzyme activities in Drosophila. I. The detection of regulatory loci by gene dosage responses

In order to detect regulatory genetic sites in the autosomes ofDrosophila melanogaster, the levels of X-linked glucose-6-phosphate dehydro-genase and autosomally linked α-glycerophosphate and isocitrate dehydrogenases have been monitored in extracts of flies aneuploid for regions of chromosomes II and III. In addition to expected structural gene dosage responses of α-GPDH and IDH, flies hyperploid for several autosome regions were found to display altered levels of one or more of the enzymes studied. While IDH activity was increased in flies hyperploid for segments of both chromosomes II and III, α-GPDH activity was decreased in specific hyperploids for chromosome II regions only. The latter group of segmental aneuploids were normal with respect to levels of chromosome II-linked alcohol dehydrogenase. To test if the observed responses were due to dosage changes of discrete genes lying within the larger effective segments, flies aneuploid for subdivisions of the chromosome segments 21A-25CD, 35A–40, and 70CD–71B were assayed. For two of these large segments so analysed, the apparent effects were attributable to specific small subdivisions, suggesting the presence of discrete regulatory sites within the latter. For the 35A–40 region the α-GPDH effect observed for subdivisions was not sufficient to account for the large α-GPDH decrease seen in flies hyperploid for the large, inclusive region. These observations are discussed with respect to the possible bases of effect of regulatory elements on enzyme activity.

GENETICS OF A PRIMARY TRISOMIC SERIES IN BARLEY: IDENTIFICATION BY PROTEIN ELECTROPHORESIS

Disc electrophoresis of seed proteins identified the extra chromosome involved in primary trisomics of barley. Each of the seven primary trisomics could be distinguished from diploids and from each other. Electrophoresis provided a precise biochemical criterion for identification of trisomics.