Case report of de novo dup(18p)/del(18q) and r(18) mosaicism

This is a report of a 27-year-old woman with an unusual de novo chromosomal abnormality. Mosaicism was identified in peripheral blood cells examined by standard G-bands by trypsin using Giemsa (GTG) analysis and fluorescence in situ hybridization (FISH) analysis with chromosome-18 region-specific probes, 46,XX,del(18)(pter → q21.33:)[41], 46,XX,r(18)(::p11.21 → q21.33::)[8], and 46,XX,der(18)(pter → q21.33::p11.21 → pter)[1]. On the other hand, the karyotype of periodontal ligament fibroblasts was nonmosaic, 46,XX, der(18)(pter → q21.33::p11.21 → pter)[50]. All cell lines appeared to be missing a portion of 18q (q21.33 → qter). The pattern of the dup(18p)/del(18q) in the rod configuration raises the possibility of an inversion in chromosome 18 in one of the parents. However, no chromosomal anomaly was detected in either parent. The most probable explanation is that de novo rod and ring configurations arose simultaneously from an intrachromosomal exchange. The unique phenotype of this patient, which included primary hypothyroidism and primary hypogonadism, is discussed in relation to her karyotype.