Neocentric Supernumerary Ring Chromosome 8 Balanced With Homolog Deletion Along With Presence of a 7.4 Mb Deletion of 2q24.3q31.1 in a Child With Seizures

We present a case of a 17 month-old girl with a seizure disorder. Chromosome analysis showed two cell lines. All cells had a small interstitial deletion of 2q24.3q31.1 along with an interstitial deletion in chromosome 8 at 8q21.1q24.23. A ring chromosome 8 with a presumed neocentromere was present in all cells with doubling of the ring in about half of metaphase cells examined. The karyotype for this study was described as: mos 47,XX,del(2)(q24.3q31.1),del(8)(q21.12q24.23),+r(8)(::q21.12- >q24.23::)[3]/ 47,XX,del(2)(q24.3q31.1),del(8)(q21.12q24.23),+r(8)dup(8)(::q21.12- >q24.23::q21.12- >q24.23::)[2]. Single nucleotide polymorphism chromosomal microarray (SNP CMA) studies defined the deletion of chromosome 2q as a 7.4 Mb loss at 166,750,943-174,149,401 which involves multiple Reference Sequence genes including 12 OMIM disease genes. However, SNP microarray revealed no gains or losses of genomic material on chromosome 8. In this case, the supernumerary ring appears to balance the corresponding homolog deletion, though, ring instability may result in low level mosaicism for monosomy or trisomy. While disruption of genes involved in the 8q cannot be excluded, our patient's phenotype can be attributed to the 7.4 Mb loss within 2q. Results of parental cytogenetic studies support de novo chromosomal anomalies in the child. These findings underscore the importance of a complete genomic laboratory testing to include cytogenetic analysis together with chromosomal microarray.