TRISOMY 7P RESULTING FROM ISOCHROMOSOME FORMATION AND WHOLE-ARM TRANSLOCATION

A newborn boy with a large anterior fontanel, minor facial anomalies, postaxial polydactyly, patent ductus arteriosus, and developmental del ay had trisomy of 7p due to an i(7p) and a concomitant t(2;7) (q37.3; q11.1), Significant enlargement of the fontanel is the most characteri stic finding in most patients with duplications involving 7p15-pter, A synchrony in fore- and hindbrain and hemisphere formation leading to b rain asymmetry and various defects in the posterior fossa are typical of infants with duplications of 7p11-p12, A variety of heart defects h as also been found in more than 50% of patients with duplication of 7p segments. Isochromosome formation accompanied by whole-arm translocat ion, resulting in uniparental isodisomy for the involved segment, is a n extremely rare cause leading to partial trisomies, Although it is no t clear whether isochromosome formation precedes the whole-arm translo cation or follows it, the secondary rearrangement may have adaptive si gnificance. (C) 1995 Wiley-Liss, Inc.