Partial trisomy 1q and monosomy 18q due to a de novo t(1;18)(q25;q23).

A two-year-old girl trisomic for the segment 1q25 leads to qter and partially monosomic for band 18q23 as a consequence of a de novo t(1;18)(q25;q23) is reported. Most of the proposita's clinical findings have been described in the 1qter trisomy and some others in the 18q monosomy. This observation is interpreted as additional evidence of epi-, iso-, and hypostatic interactions at the chromosomal level.