INHERITED STRUCTURAL CYTOGENETIC ABNORMALITIES DETECTED INCIDENTALLY IN FETUSES DIAGNOSED PRENATALLY - FREQUENCY, PARENTAL-AGE ASSOCIATIONS, SEX-RATIO TRENDS, AND COMPARISONS WITH RATES OF MUTANTS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 36  (2) , 422-443
Abstract
Rates of structural chromosome abnormalities were analyzed in 24,951 fetuses studied prenatally in which there were no grounds to suspect an inherited abnormality. In about 1 of 200 prenatal cytogenetic diagnoses, an unexpected structural abnormality was found. The observed rate was 5.3/1000, of which 1.7/1000 were unbalanced and 3.6/1000 balanced. The rate of inherited abnormalities was 3.1-3.7 per 1000 (0.4-0.9 per 1000 for unbalanced abnormalities and 2.6-2.8/1000 for balanced abnormalities). The rate of mutants in this series was, by contrast, 1.6-2.2/1000 (0.8-1.2/1000 for unbalanced abnormalities and 0.8-1.0/1000 for balanced abnormalities). The rate of balanced Robertsonian translocation carriers was 0.6/1000 (about 0.25/1000 for mutants and 0.35/1000 for inherited abnormalities), and for other balanced abnormalities, 3.0/1000 (about 0.6/1000 for mutants and 2.4/1000 for inherited abnormalities). The rates of unbalanced Robertsonian translocations was about 0.1/1000, almost all of which were mutants. For supernumerary rearrangements, the rate was 0.9/1000 (about 0.4/1000 inherited and 0.5/1000 mutant). The rates of all unbalanced (nonmosaic) inherited abnormalities (4.0-5.2/10,000) were intermediate between higher rates estimated in all conceptuses (9.1-15.8/10,000) and rates observed in newborns (1.5-2.5/10,000). This trend is probably attributable to fetal mortality associated with unbalanced rearrangements. The rates of balanced (nonmosaic) inherited abnormalities (26.0-28.0/10,000), however, were considerably higher than the rates in all conceptuses (13-16.7/10,000) or in all live births (12.2-16.0/10,000). The major difference was in the rate of inversions. The use of banding methods in the studies of amniocentesis but not in most of the live births or abortus studies probably contributes to at least some of these differences. One trend in parental age among the inherited abnormalities was noteworthy. Paternal age was elevated for inherited balanced reciprocal structural abnormalities of paternal origin but not of maternal origin. With regard to sex ratio, there was a greater proportion of females than males among the unbalanced rearrangements both inherited and mutant. There was no obvious sex difference among the balanced rearrangements.