Partial tetrasomy 9 in a liveborn infant.

An unusual rearrangement of chromosome 9 was identified in a male infant with multiple congenital malformations. The rearrangement appeared as a fusion of two number 9 chromosomes with similar long-arm breakpoints. Since the infant also possessed two normal 9's, the presence of the additional chromosome resulted in partial tetrasomy; 47,XY, + tdic(9;9)(q22;q22). Clinical and autopsy examinations revealed many features reminiscent of trisomy 13. The tdic was functionally monocentric, although some evidence of activity at the second centromere was observed. Both parents had normal karyotypes, and C-banding demonstrated that at least one of the 9h regions on the tdic was likely to be of maternal origin.