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Open Access Highly Accessed Case report

The utility of exome sequencing for genetic diagnosis in a familial microcephaly epilepsy syndrome

Laura M McDonell1, Jodi Warman Chardon2, Jeremy Schwartzentruber3, Denise Foster4, Chandree L Beaulieu1, FORGE Canada Consortium1, Jacek Majewski5, Dennis E Bulman16 and Kym M Boycott126*

Author Affiliations

1 Children’s Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada

2 Department of Genetics, Children’s Hospital of Eastern Ontario, Ottawa, Ontario, Canada

3 McGill University and Genome Quebec Innovation Centre, Montréal, Quebec, Canada

4 Algoma Public Health, Sault Ste Marie, Ontario, Canada

5 Department of Human Genetics, McGill University, Montréal, Quebec, Canada

6 Department of Pediatrics, University of Ottawa, Ottawa, Ontario, Canada

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BMC Neurology 2014, 14:22  doi:10.1186/1471-2377-14-22

Published: 31 January 2014

Abstract

Background

Despite remarkable advances in genetic testing, many adults with syndromic epilepsy remain without a molecular diagnosis. The challenge in providing genetic testing for this patient population lies in the extensive genetic heterogeneity associated with epilepsy. Even for the subset of epilepsy patients that present with a defining feature, such as microcephaly, the number of possible genes that would require interrogation by Sanger sequencing is extensive and often prohibitively expensive.

Case presentation

We report a family of French Canadian descent with four adult children affected with severe intellectual disability, epilepsy and microcephaly born to consanguineous parents and evaluated by the Genetics Service to provide informed genetic counseling to unaffected family members regarding possible recurrence risks. We used whole-exome sequencing (WES) of DNA from one affected sibling as a first-line diagnostic tool and compared the prioritization of variants using two strategies: 1) focusing on genes with homozygous variants; and, 2) focusing on genes associated with microcephaly. Both approaches prioritized the same homozygous novel frameshift mutation (p.Arg608Serfs*26) in WDR62, a gene known to cause autosomal recessive primary microcephaly. Sanger sequencing confirmed the presence of the homozygous mutation in the other three affected siblings.

Conclusions

WES and subsequent filtering of the rare variants in a single affected family member led to the rapid and cost-effective identification of a novel homozygous frameshift mutation in WDR62, thereby explaining the severe neurodevelopmental disorder in this family and facilitating genetic counseling. Our findings support WES as an effective first-line diagnostic tool in families presenting with rare genetically heterogeneous neurological disorders.

Keywords:
Primary microcephaly; Epilepsy; Whole-exome sequencing; WDR62