Trisomy 18 phenotype in a patient with an isopseudodicentric 18 chromosome.

We report a female patient with a typical trisomy 18 phenotype who has a 46,XX, -18, +isopseudodic(18)(p11) karotype. The lack of features of the 18p- syndrome suggests that a significant amount of short arm material is present and that the Turner-like features associated with 18p- may be determined by monosomy for 18p11. The phenotype-genotype correlations in abnormalities affecting chromosome 18 are reviewed.