Abstract 3814: Exome sequencing for identification of causative genes for mosaic variegated aneuploidy.
Authors: Peddibhotla Sirisha , Powell Bradford , Patel Meha P. , Rao Pulivarthi H. , Wheeler David A. , Gibbs Richard A. , Plon Sharon E. 
Published: August 2014

Mosaic Variegated Aneuploidy (MVA: OMIM 257300) is a rare autosomal recessive syndrome associated with growth deficiency of prenatal onset, microcephaly, intellectual disability, anomalies of the central nervous system, mild physical dysmorphic features and predisposition to cancer. Of the 37 reported cases of MVA, the cancers reported include Wilms tumor, rhabdomyosarcoma and leukemia. The cells from MVA patients demonstrate variable whole chromosome loss and gains suggesting an underlying chromosome segregation dysfunction. Previous studies have demonstrated biallelic loss-of-function mutations in mitotic spindle-assembly checkpoint gene BUB1B or a centrosomal microtubule stabilizing gene CEP57 in some MVA patients. Therefore, the goal of this project is to identify novel causative genes that contribute to the development of MVA.

We have identified one patient diagnosed with clinical features of MVA associated with myelodysplasia and acute myeloid leukemia. Cytogenetic analysis of peripheral blood karyotype demonstrated low-level mosaicism with multiple clones of various chromosomal gains such as trisomy 1, 5, 6, 8 and 18. Molecular sequence analysis confirmed normal BUB1B and CEP57 in this patient. Therefore, whole-exome sequencing is being used as an approach to identify disease-causing genes in our patient. Exome data analysis assuming an autosomal recessive model and Sanger sequencing confirmed four putative genes with biallelic mutations in AIM1 (absent in melanoma 1), EPS15 (epidermal growth factor receptor substrate 15), MICALL2 (molecule interacting with CasL-like protein 2) and ZSCAN12 (zinc finger and SCAN domain containing 12). Review of literature reveals potential roles of these genes on cytoskeleton, mitotic spindle formation and cytokinesis.

To further investigate these potential loci in our MVA patient, we designed cellular and functional assays using patient skin fibroblasts. Using interphase-FISH analysis, we have recapitulated the aneuploidy phenotype with abnormal chromosome numbers involving trisomy 8 in the patient skin fibroblasts. Moreover, immunocytochemistry with cytoskeletal and mitotic markers display aberrant anaphase with dysfunctional spindle mid-zone and cytokinesis failure. In addition, the patient fibroblasts also exhibited increased percentage of binucleated and micronucleated progeny due to abnormal chromosome segregation and cytokinesis. In summary, exome sequencing revealed a small number of potential causative genes as the etiology of MVA in our patient. Our early results demonstrate biomarkers for chromosome instability and aneuploidy such as non-disjunction, cytokinesis failure, micronuclei and binucleation in patient fibroblasts. Further work will determine whether dysregulation of these candidate genes can recapitulate this instability phenotype leading to mosaic aneuploidy in our patient.

Citation Format: Sirisha Peddibhotla, Bradford Powell, Meha P. Patel, Pulivarthi H. Rao, David A. Wheeler, Richard A. Gibbs, Sharon E. Plon. Exome sequencing for identification of causative genes for mosaic variegated aneuploidy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3814. doi:10.1158/1538-7445.AM2013-3814