Rare diseases are not necessarily that rare: They affect some four million people in Germany alone. But of the estimated 8,000 different diseases that fall into this category, there are usually only a few recorded cases of each one. As a result, it can take years for those affected to receive the correct diagnosis – and yet this is a prerequisite for effective therapy. “The parents of affected children often end up sitting across from us after a long and arduous journey,” says Dr. Nadja Ehmke, a specialist at the Charité’s Institute of Medical Genetics and Human Genetics. “They have a sick child who is not developing properly, either mentally or physically, and they want to know why. If we can use a genetic analysis to explain to them where the defect lies, this is often a huge relief for the parents – even if it does not necessarily mean anything can be done for their child in terms of treatment.” Such knowledge enables parents to exchange information with others in the same situation, to visit or set up self-help groups, and to better assess whether another child could also fall ill.
Powerful software detects differences
To conduct the genetic analysis, scientists isolate the genetic material from patients’ blood cells, read the sequence – i.e., the order of letters – and compare it with the genetic material of parents, siblings or existing genetic analyses in large databases. “This is where humans reach their natural limits,” reports Dr. Dieter Beule, head of the Bioinformatics Core Unit at the Berlin Institute of Health (BIH) and at the MDC. “Even if we only analyze the protein-coding regions of the genetic material, the so-called exome, there are millions of building blocks to compare. We require powerful software to detect the differences.” But even in the genetic material of two healthy individuals, there are around 30,000 positions in these coding regions (alone) that differ.
Which of the many variants is the cause of the illness? This was the very question that motivated Dieter Beule and his team to develop VarFish. VarFish compares the patient’s sequence with sequences from worldwide databases. The Bioinformatics Core Unit scientists made use of many open and free data resources, including the U.S. databases of the National Center for Biotechnology Information (NCBI) at the University of Washington in Seattle, and the European Bioinformatics Institute (EBI) in Cambridge, UK, as well as Charité’s and the BIH’s own databases and algorithms.
Adjustment within seconds
“In a matter of seconds, VarFish can eliminate 29,950 of the 30,000 differences,” explains Dieter Beule. “This is because the software finds many of the same deviations, for example, in the sequences from population samples, where it apparently does not lead to noticeable problems and is therefore in all probability not responsible for the rare disease.” The scientists can then compare the remaining 50 gene variants with known hereditary diseases, thus narrowing down the group of possible culprits to about ten genetic mutations.
In some cases, scientists may also discover mutations in a known gene during their research. “VarFish enables rapid testing for mutations in known genes,” explains Professor Ute Scholl, who holds a Johanna Quandt Professorship at the BIH. “This is important, as it can give us clues as to which drug may be able to help and should be studied further in clinical trials.” If there are no mutations in known genes, VarFish can be used to identify a new candidate gene within a larger family or by comparing several affected families with the same disease. The outcome produced by mutations in such a candidate gene can then often be determined in the laboratory. Ute Scholl’s lab introduces the mutated genes into cell cultures or mice and observes what effects the mutation has. “Using this method, we have recently characterized a new gene for a rare inherited form of high blood pressure,” reports the physician. But drug development and even targeted treatment are still some way off: “First, we want to understand how the disease develops in the first place and where the symptoms originate.”
Fast and accurate diagnosis
Dr. Manuel Holtgrewe, lead author of the paper, is delighted that the new software is finding so many users: “In just the first few weeks, VarFish has been used hundredfold by scientists and doctors around the world. In our own laboratory we analysed thousands of data sets with the help of VarFish.” International cooperation is particularly important in the research and treatment of rare diseases, as each individual mutation usually occurs only a few times in each country. Professor Stefan Mundlos, head of the Institute for Medical Genetics and Human Genetics at Charité and the Development and Disease Group at the Max Planck Institute for Molecular Genetics in Berlin, reports: “VarFish has been very helpful in enabling us to quickly and accurately diagnose participants for our clinical trials.”
Manuel Holtgrewe and Dieter Beule are now planning to expand VarFish so as to enable the genome-wide analysis of so-called structural variants. In addition, further functions will be added for the effective and safe cross-locational collaboration of human geneticists. “VarFish supports users in the analysis of their molecular genetic data in both basic research and clinical application,” says Dieter Beule. “The core mission of the BIH is translation – which involves transferring results from research to the clinic and, vice versa, bringing clinical observations back to the lab. With our software VarFish, we are supporting this very goal.”
Holtgrewe, Manuel et al. (2020): “”. Nucleic Acids Research, DOI: .
The Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC) was founded in Berlin in 1992. It is named for the German-American physicist Max Delbrück, who was awarded the 1969 Nobel Prize in Physiology and Medicine. The MDC's mission is to study molecular mechanisms in order to understand the origins of disease and thus be able to diagnose, prevent and fight it better and more effectively. In these efforts the MDC cooperates with the Charité - Universitätsmedizin Berlin and the Berlin Institute of Health (BIH) as well as with national partners such as the German Center for Cardiovascular Research and numerous international research institutions. More than 1,600 staff and guests from nearly 60 countries work at the MDC, just under 1,300 of them in scientific research. The MDC is funded by the German Federal Ministry of Education and Research (90 percent) and the State of Berlin (10 percent), and is a member of the Helmholtz Association of German Research Centers.
The mission of the Berlin Institute of Health (BIH) is medical translation: transferring biomedical research findings into novel approaches to personalized prediction, prevention, diagnostics and therapy and, conversely, using clinical observations to develop new research ideas. The aim is to deliver relevant medical benefits to patients and the population at large. The BIH is also committed to establishing a comprehensive translational ecosystem – one that places emphasis on a system-wide understanding of health and disease and that promotes change in the biomedical research culture. The BIH is funded 90 percent by the Federal Ministry of Education and Research (BMBF ) and 10 percent by the State of Berlin. The two founding institutions, Charité – Universitätsmedizin Berlin and Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), are independent member entities within the BIH.