A child with multiple congenital anomalies was referred for cytogenetic evaluation. G-banded analysis showed a complex chromosome rearrangement involving 6 different chromosomes and 10 breakpoints. Fluorescence in situ hybridization (FISH) using whole chromosome painting probes and repetitive sequence probes was performed. In most cases the painting probes alone helped to clarify the G-banded results. However, in one instance, where the terminal band of the long arm of chromosome 1 was involved, the use of a telomeric probe was essential in defining the rearrangement.

A genetics evaluation was requested for a 6‐week‐old infant with multiple congenital malformations including mild craniofacial anomalies, truncal hypotonia, hypospadias, and a ventriculoseptal defect. Blood obtained for chromosome analysis revealed an abnormal chromosome 4. Paternal chromosome analysis showed a 46,XY, inv ins (3;4) (p21.32; q25q21.2), inv(4)(p15.3q21.2) karyotype. Therefore, the proband's chromosome 4 was the unbalanced product of this insertional translocation from the father resulting in partial monosomy 4q. Additionally, the derivative 4 had a pericentric inversion which was also seen in the father's chromosome 4. During genetic counseling, the proband's 2‐year‐old brother was evaluated. He was not felt to be abnormal in appearance, but was described as having impulsive behavior. Chromosome analysis on this child revealed 46,XY,der(3)inv ins(3;4)(p21.32;q25q21.2)pat. This karyotype results in partial trisomy 4q. FISH using two‐color “painting” probes for chromosomes 3 and 4 confirmed the G‐banded interpretation in this family. The segregation seen in this family resulted in both reciprocal products being observed in the two children, with partial 4q monosomy showing multiple congenital anomalies, and partial 4q trisomy showing very few phenotypic abnormalities. © 1995 Wiley‐Liss, Inc.