A case of insertional translocation involving chromosomes 2 and 4.

We report on a 6-year-old Caucasian boy with direct insertion of genetic material from the short arm of chromosome 4 to the short arm of chromosome 2. He was referred for evaluation because of global developmental delay and seizure disorder. A karyotype performed at 4 1/2 months of age, by a laboratory elsewhere, reportedly showed a deletion of chromosome 4(p12). When we saw him, he had macrocephaly, hypotonia, psychomotor retardation, multiple minor congenital anomalies, and EEG abnormalities. Repeat chromosomes performed by our laboratory revealed that his karyotype was 46,XY,dir ins(2;4)(p24;p15.3p13). Fluorescence in situ hybridization (FISH) analysis, using chromosomes 2 and 4 painting probes confirmed that material from 4p has been translocated to 2p. Also, FISH analysis using the Wolf-Hirschhorn critical region probe revealed that both loci are intact. Parental chromosomes were normal. This complex rearrangement, though it appears balanced, probably might have resulted in either a structural loss of genetic material or functional loss of a gene action. Thus, his phenotype could be explained by this de novo insertion of chromosome 4 material into chromosome 2. There is no reported case of this specific chromosome rearrangement.