Partial trisomy 18q in a newborn with typical 18 trisomy phenotype.

This paper describes a case of partial trisomy of almost the entire long arm of chromosome 18 in a newborn with classic trisomy-18 phenotype, resulting from a de novo unbalanced 181/21p translocation: karyotype: 46,XX,-21,t(18;21)(18qter leads to 18q11 ::21p12 leads to 21qter). A review of the other reported cases of partial trisomy 18 suggests that a critical segment in chromosome 18, corresponding to bands q11-q12, might be responsible for most of the signs of trisomy 18, including failure to thrive and early death.