Next‐generation DNA sequencing of HEXA: a step in the right direction for carrier screening

Jodi D Hoffman,Gregory J Porreca,Caleb Kennedy,Jaclyn Schienda,Stephanie Hallam,Charles Towne,Mark A Umbarger,Miriam G Blitzer,Jocelyn Davie,Valerie Greger,Brian Bishop,Patrick Saunders,Erin T Strovel

doi:10.1002/mgg3.37

Abstract

Tay-Sachs disease (TSD) is the prototype for ethnic-based carrier screening, with a carrier rate of ∼1/27 in Ashkenazi Jews and French Canadians. HexA enzyme analysis is the current gold standard for TSD carrier screening (detection rate ∼98%), but has technical limitations. We compared DNA analysis by next-generation DNA sequencing (NGS) plus an assay for the 7.6 kb deletion to enzyme analysis for TSD carrier screening using 74 samples collected from participants at a TSD family conference. Fifty-one of 74 participants had positive enzyme results (46 carriers, five late-onset Tay-Sachs [LOTS]), 16 had negative, and seven had inconclusive results. NGS + 7.6 kb del screening of HEXA found a pathogenic mutation, pseudoallele, or variant of unknown significance (VUS) in 100% of the enzyme-positive or obligate carrier/enzyme-inconclusive samples. NGS detected the B1 allele in two enzyme-negative obligate carriers. Our data indicate that NGS can be used as a TSD clinical carrier screening tool. We demonstrate that NGS can be superior in detecting TSD carriers compared to traditional enzyme and genotyping methodologies, which are limited by false-positive and false-negative results and ethnically focused, limited mutation panels, respectively, but is not ready for sole use due to lack of information regarding some VUS.

Highlights

Tay-Sachs disease (TSD) is an autosomal recessive neurodegenerative disease that has served as the prototype for ethnic-based screening programs throughout the world
After Tufts University School of Medical Institutional Review Board approved informed verbal consent was obtained from each participant, peripheral blood samples were collected for both TSD enzyme analysis and next-generation DNA sequencing (NGS) analysis
Five participants reported being affected with late-onset Tay-Sachs disease (LOTS); 36 participants reported themselves as obligate carriers, 11 as carriers for TSD, eight as noncarriers, and one as a carrier for a pseudodeficiency allele

Summary

Introduction

Tay-Sachs disease (TSD) is an autosomal recessive neurodegenerative disease that has served as the prototype for ethnic-based screening programs throughout the world. In the early 1970s, Jewish communities designed screening programs for the detection of TSD carrier status (Kaback et al 1993). The initial TSD screening programs were very successful in providing Jewish individuals and couples with information to allow for the birth of unaffected offspring through reproductive technologies or mate selection. By 1992, almost one million individuals had been screened and the number of children born with TSD to AJs had decreased from ~45 to 3–4 per year, lower than the incidence in the non-Jewish population (Kaback et al 1993)

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Results

Conclusion