Identifying the cause of mosaic variegated aneuploidy in a child through exome sequencing

Mosaic variegated aneuploidy (MVA) is a genetic condition in which abnormal mitoses lead to abnormal numbers of chromosomes in subpopulations of cells within the body. This condition is associated with a variety of medical problems, developmental delay and predisposition to certain forms of cancer. MVA is an autosomal recessive condition where prior studies have reported biallelic mutations in either the BUB1B and CEP57 genes, both of which function in the mitotic spindle checkpoint. We are studying a patient who presented with myelodysplasia and microcephaly and was found to have peripheral blood cells of varying chromosome numbers consistent with a diagnosis of MVA. Molecular testing for BUB1B was negative. We hypothesized that exome sequencing of the DNA of the patient and both parents would identify the molecular cause of MVA in this patient.  Exome sequencing did not reveal potential disease-causing mutations in BUB1B or CEP57.  We identified six genes containing rare biallelic mutations in the patient.  Sanger sequencing was performed on the DNA of the patient and both parents in order to validate the mutations identified through next generation sequencing and confirm the parental phase of these mutations. We are using western blot analysis to measure the expression of the encoded protein products in cell lines from the patient, parents, and control cell lines. We will then characterize the mitotic properties of cells in response to knockdown of expression of these genes by siRNA methods to functionally test which gene is likely the cause of MVA in this patient.