Background. Several cases have been reported of patients with a ring chromosome 18 replacing one of the normal chromosomes 18. Less common are patients with a supernumerary ring chromosomes 18. High resolution whole genome examination in patients with multiple congenital abnormalities might reveal cytogenetic abnormalities of an unexpected complexity. Results. We report a 24 years old male patient with lower spinal anomalies, hypospadia, bifid scrotum, cryptorchism, anal atresia, kidney stones, urethra anomalies, radial dysplasia, and a hypoplastic thumb. Some of the anomalies overlap with the VACTERL association. Chromosome analysis of cultured peripheral blood lymphocytes revealed an additional ring chromosome in 13% of the metaphases. Both parents had a normal karyotype, demonstrating the de novo origin of this ring chromosome. FISH analysis using whole chromosome paints showed that the additional chromosomal material was derived from chromosome 18. Chromosome analysis of cultured fibroblasts revealed only one cell with the supernumerary ring chromosome in the 400 analyzed. To characterize the ring chromosome in more detail peripheral blood derived DNA was analyzed using SNP-arrays. The array results indicated a 5 Mb gain of the pericentromeric region of chromosome 18q10-q11.2. FISH analysis using BAC-probes located in the region indicated the presence of 6 signals on the r(18) chromosome. In addition, microsatellite analysis demonstrated that the unique supernumerary ring chromosome was paternally derived and both normal copies showed biparental disomy. Conclusions. We report on an adult patient with multiple congenital abnormalities who had in 13% of his cells a unique supernumerary ring chromosome 18 that was composed of 6 copies of the 5 Mb gene rich region of 18q11.

adult, anus atresia, article, bone dysplasia, case report, chromosome 18q, chromosome analysis, congenital malformation, cryptorchism, female, fluorescence in situ hybridization, human, hypospadias, karyotype, male, metaphase, nephrolithiasis, peripheral lymphocyte, priority journal, ring chromosome, single nucleotide polymorphism, spine malformation, urethra malformation,
Molecular Cytogenetics
Erasmus MC: University Medical Center Rotterdam

van der Veken, L.T, Dieleman, M.M.J, Douben, H, van de Brug, J.C, van de Graaf, R, Hoogeboom, A.J.M, … de Klein, J.E.M.M. (2010). Low grade mosaic for a complex supernumerary ring chromosome 18 in an adult patient with multiple congenital anomalies. Molecular Cytogenetics, 3(1), 1–10. doi:10.1186/1755-8166-3-13