[Tetrasomy 9p]

A newborn male with multiple malformations and an extrachromosome is presented. The cytogenetic study of peripheral blood lymphocytes revealed tetrasomy 9p: 47,XY, + t(9;9)(pter----q13::p11----pter). The C-banding pattern provided evidence for maternal origin of the extrachromosome. Tetrasomy for the short arm of chromosome 9 is a very rare condition; reports about only ten further patients have been found in the literature. The phenotypic expression resembles trisomy 9p, but tetrasomy 9p has more severe additional malformations.