Dicentric chromosome 9 due to tandem duplication of the 9p11‐q13 region: Unusual chromosome 9 variant

We report on a 31‐year‐old mentally retarded woman with minor facial anomalies and a heteromorphic chromosome 9 with tandem duplication of the 9p11‐q13 pericentromeric region. To the best of our knowledge, this is the first report of tandem duplication of this region. An identical chromosome 9 morphology was found in the healthy and phenotypically normal sister of the proposita. The usefulness of double‐color FISH techniques and the presumed mechanism accounting for the origin of the chromosomal anomaly and for the phenotypic discordance observed between the two sisters are discussed. Am. J. Med. Genet. 93:192–197, 2000. © 2000 Wiley‐Liss, Inc.