FISH studies identify the i(20q-) anomaly as a der(20)del(20)(q11q13)idic(20)(p11).

Fluorescence in situ hybridization (FISH) analyses were performed on six of seven patients who had been reported in 2004 to have an i(20q-) anomaly expressed as ider(20)(q10)del(20)(q11q13). The i(20q-) was investigated with a series of probes: a centromere-specific probe for chromosome 20, two paint probes for 20p and 20q, and a panel of locus-specific probes prepared from BAC/PAC clones mapped to 20p. The results showed that: (1) i(20q-) was a dicentric chromosome; (2) both of its arms comprised a deleted 20q and a small part of 20p near the centromere of chromosome 20; and (3) the breakpoints and reunion sites of i(20q-) differed, residing in the region 20p11.21-20p11.22 delineated by BAC/PAC clones RP11-96L6 and RP13-401N8. Thus, i(20q-) could be more precisely described as a der(20)del(20)(q11q13)idic(20)(p11).