Unravelling undiagnosed rare disease cases by HiFi long-read genome sequencing.

Solve-RD is a pan-European rare disease (RD) research program that aims to identify disease-causing genetic variants in previously undiagnosed RD families. We utilised 10-fold coverage HiFi long-read sequencing (LRS) for detecting causative structural variants (SVs), single nucleotide variants (SNVs), insertion-deletions (InDels), and short tandem repeat (STR) expansions in extensively studied RD families without clear molecular diagnoses. Our cohort includes 293 individuals from 114 genetically undiagnosed RD families selected by European Rare Disease Network (ERN) experts. Of these, 21 families were affected by so-called 'unsolvable' syndromes for which genetic causes remain unknown, and 93 families with at least one individual affected by a rare neurological, neuromuscular, or epilepsy disorder without genetic diagnosis despite extensive prior testing. Clinical interpretation and orthogonal validation of variants in known disease genes yielded thirteen novel genetic diagnoses due to de novo and rare inherited SNVs, InDels, SVs, and STR expansions. In an additional four families, we identified a candidate disease-causing SV affecting several genes including an MCF2 / FGF13 fusion and PSMA3 deletion. However, no common genetic cause was identified in any of the 'unsolvable' syndromes. Taken together, we found (likely) disease-causing genetic variants in 13.0% of previously unsolved families and additional candidate disease-causing SVs in another 4.3% of these families. In conclusion, our results demonstrate the added value of HiFi long-read genome sequencing in undiagnosed rare diseases.

Accepting or declining preconception expanded carrier screening: An exploratory study with 407 couples.

Rapidly evolving genomic technologies have made genetic expanded carrier screening (ECS) possible for couples considering a pregnancy. The aim of ECS is to identify couples at risk of having a child affected with a severe disorder and to facilitate their reproductive decision-making process. The ECS test we offer at our center, called BeGECS (Belgian Genetic ECS), consists of 1268 autosomal recessive (AR) and X-linked pathogenic genes, including severe childhood-onset disorders. However, thus far data are scarce regarding the actual uptake of preconception ECS in a clinical setting. Therefore, our aim was to describe the characteristics of 407 couples to whom ECS was offered at the Center for Medical Genetics of the University Hospital Ghent (CMGG). In addition, we aimed to identify their reasons for accepting or declining BeGECS. Between October 2019 and January 2023, 407 preconception couples were offered BeGECS and were asked to fill in a questionnaire after their decision. Of the 407 couples participating in the survey, 270 (66%) decided to take the test and 137 (34%) declined. We observed that age, highest education level as well as indication for consultation were statistically different between the group that accepted to take the test and the group that declined (p = 0.037). In particular, age and education level were substantially higher in the group that accepted the test. Major reasons for taking BeGECS include prevention, wishing to obtain all information possible, helping preparing their future reproductive decision and increasing their sense of control by being informed. However, couples that do not chose to take BeGECS stated that too much information would make them anxious, that the result would not change their decision to have children, that they do not want to spend money on something that will not happen and that they do not worry about their family history. These findings show that the majority of preconception couples that were offered ECS, accepted the test.