SATELLITED 4Q IDENTIFIED IN AMNIOTIC-FLUID CELLS

Extra material was identified on the distal long arm of a chromosome 4 in an amniotic fluid specimen sampled at 16.6 weeks of gestational ag e. There was no visible loss of material from chromosome 4, and no evi dence for a balanced rearrangement. The primary counseling issue in th is case was advanced maternal age. Ultrasound findings were normal, an d family history was unremarkable. The identical. 4qs chromosome was o bserved in cells from a paternal peripheral blood specimen and appeare d to be an unbalanced rearrangement. This extra material was NOR posit ive in lymphocytes from the father, but was negative in the fetal amni ocytes. Father's relatives were studied to verify the familial origin of this anomaly. In situ hybridization with both exon and intron seque nces of ribosomal DNA demonstrated that ribosomal DNA is present at th e terminus of the 4qs chromosome in the fetus, father, and paternal gr andmother This satellited 4q might have been derived from a translocat ion event that resulted in very little or no loss from the 4q and no s pecific phenotype. This derivative chromosome 4 has been inherited thr ough at least 3 generations of phenotypically normal individuals. (C) 1995 Wiley-Liss, Inc.