A high frequency of structural chromosome abnormalities in a south central texas cytogenetics laboratory

Abnormalities of chromosome number, such as the autosomal trisomies and sex chromosome aneuploidies, are considered to be sporadic events with low and constant recurrence risk across populations. On the other hand, abnormalities of chromosome structure can be generated by environmental agents and also transmitted in families and therefore may accumulate in certain populations. Evidence from several geographically diverse newborn infant screening studies and from clinical cytogenetics laboratories (including our own) supports the hypothesis that the frequency of structural abnormalities varies among populations, whereas the frequency of numerical abnormalities remains relatively constant among populations. The data from our laboratory, based on 1,201 patients over a 6-year period, suggest a two- to nearly fourfold higher frequency of structural defects over that of other populations (8.8% vs 4.2% and 2.5% of samples tested). Some of the problems associated with making comparisons among the published data sets are discussed, along with alternative explanations for the variability in the frequency of structural defects reported in different populations.