In some GENEVA subjects, anomalies appear to have occurred early enough in development to be mosaic in both the soma and germline. In 35 parent-offspring pairs in which a mosaic anomaly was detected in the parent, there are three cases in which the offspring appears to be non-mosaic for the same anomaly (one deletion and two duplications), while there is no corresponding anomaly (mosaic or otherwise) in the remaining 32 offspring. Although this result suggests that a fairly large fraction of cases have mosaicism shared by the germline and soma, it may not be representative of the more frequent mosaics that occur in older subjects because parents in the family studies were sampled in their 20s and 30s (Table 1). The mosaics that appear in subjects less than 50 years of age may have different origins than those that appear later, when the frequency increases rapidly.
