MOLECULAR CHARACTERIZATION OF 21P-VARIANT CHROMOSOME

Fortuitously, within a 1-month period, we were referred two individual s for routine cytogenetic amniocenteses involving one chromosome 21 fr om each patient, which had apparently lost the entire short arm and a major portion of the centromeric alphoid sequences in their amniocytes . Breakage may have occurred within alphoid sequences resulting in ext reme variants. Variations of a similar nature were originally referred to as Christchurch (Ch(1)) chromosomes and have been wrongly determin ed to be abnormal. The 21p-chromosome variants were similar in both ca ses, though they are from unrelated individuals. These rare variants, whose origins were both maternal and have no clinical consequences, we re characterized by the FISH-technique to provide a greater degree of certainty.