The incidence and carrier frequency of Tay-Sachs disease in the French-Canadian population of Quebec based on retrospective data from 24 years, 1992-2015

A registry-based population study of the HLA in Québec, Canada

As part of the worldwide effort to better characterize HLA diversity in populations, we have studied the population of Québec in Canada. This province has been defined by a complex history with multiple founder effects and migration patterns. We analyzed the typing data of 3806 individuals registered in Héma-Québec's Registry, which covered most administrative regions in Québec. Typing information was resolved at the second field level of resolution by next-generation sequencing (NGS) or by Sanger sequencing. We used the HLA-net.eu GENE[RATE] tools to estimate allele and two-locus haplotype frequencies for HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1, as well as Hardy-Weinberg equilibrium (HWE), selective neutrality, and linkage disequilibrium. The chord genetic distance was also calculated between administrative regions and was visualized using non-metric multidimensional scaling (NMDS) analysis. While most individual regions were in HWE, HWE was rejected for the province considered as a whole. Some regions exhibited signatures of selection, mostly toward an excess of heterozygotes. Allele and haplotype frequencies revealed outlier regions that strongly differed from the other regions. NMDS plots also showed differences between regions. The administrative regions of the province of Québec displayed heterogeneity in their HLA profiles. This heterogeneity was attributable to differing allele and haplotype specificities by region. In particular, regions 02-Saguenay-Lac-Saint-Jean and 01-Bas-St-Laurent diverged from the rest of the regions. The urban regions 06-Montréal and 13-Laval were very diversified in their HLA profiles. Together, these results will help optimize donor recruitment strategies in Québec.

North American genetic counselors' approach to collecting and using ancestry in clinical practice

Current guidelines from the National Society of Genetic Counselors (NSGC) recommend that patients' ancestry be obtained when taking a family history. However, no study has explored how consistently genetic counselors obtain or utilize this information. The goals of this study included assessing how genetic counselors collect their patients' ancestry, what factors influence this decision, and how they view the utility of this information. Genetic counselors working in a direct patient care setting in the US or Canada were recruited to participate in an anonymous survey via an NSGC email blast. Most participants (n = 115) obtain information about their patients' ancestry (96.5%), with the most common methods being directly asking the patient (91%) and utilizing intake forms (43.2%). Of participants who ask about ancestry directly, 50.5% always ask about the presence of Ashkenazi Jewish ancestry and 70.3% always ask about additional ancestries, suggesting that for most genetic counselors' collection of ancestry is standard practice. However, the clinical utility of ancestry information is highly variable, with the impact on genetic testing choice being particularly low. A slight majority of participants support a reevaluation of current ancestry guidelines (51.3%), with many participants suggesting that the varying utility of ancestry in different clinical indications/specialties should be incorporated into guidelines. Despite being standard practice for most genetic counselors, no unified approach or standard for how ancestral information should be used in genetic counseling practice was identified.

Increased phosphorylation of HexM improves lysosomal uptake and potential for managing GM2 gangliosidoses

Tay-Sachs and Sandhoff diseases are genetic disorders resulting from mutations in HEXA or HEXB, which code for the α- and β-subunits of the heterodimer β-hexosaminidase A (HexA), respectively. Loss of HexA activity results in the accumulation of GM2 ganglioside (GM2) in neuronal lysosomes, culminating in neurodegeneration and death, often by age 4. Previously, we combined critical features of the α- and β-subunits of HexA into a single subunit to create a homodimeric enzyme known as HexM. HexM is twice as active as HexA and degrades GM2 in vivo, making it a candidate for enzyme replacement therapy (ERT). Here we show HexM production is scalable to meet ERT requirements and we describe an approach that enhances its cellular uptake via co-expression with an engineered GlcNAc-1-phosphotransferase that highly phosphorylates lysosomal proteins. Further, we developed a HexA overexpression system and functionally compared the recombinant enzyme to HexM, revealing the kinetic differences between the enzymes. This study further advances HexM as an ERT candidate and provides a convenient system to produce HexA for comparative studies.