Atypical 18p- syndrome associated with partial trisomy 16p in a chromosomally unbalanced child of consanguineous parents with an identical balanced translocation.

A 2 month old male infant was found to have mild growth retardation, prominent forehead, low set ears, low nasal bridge, rounded facies, cleft palate, webbed neck, shawl scrotum, and absent right kidney. The propositus, a product of a consanguineous marriage, had extremely rare abnormal cytogenetic findings. His karyotype contained three derivative chromosomes that originated from a familial translocation, t(16;18)(p13.3;p11.2) carried by both parents. Based on parental studies, the infant's unbalanced karyotype was defined as: [46,XY,t(16;18)(p13.3;p11.2), der(18)t(16;18).ish t(16;18)(16ptel-,16qtel+,18ptel+,wcp16+,wcp18+;16ptel+,18ptel-,wcp16+,wcp18+), der(18)t(16;18)(16ptel+,18ptel-,wcp16+,wcp18+)]. We describe this child at 2 months of age with a follow up at 4 1/2 years, exhibiting a mixed clinical picture with features of both 18p- and partial trisomy 16p13.3.