Prof Dr H.J.M. Smeets
Mitochondrial diseases: diagnostic and therapeutic odysseys
Due to rapid developments in next-generation sequencing and other -omics technologies it has become much easier to define the genetic cause in monogenic mitochondrial diseases. A joint diagnostic and research effort identified by whole exome sequencing (WES) the genetic defect in 2/3 of a selected mitochondrial disease cohort. In the next years, knowledge of the personal genome will become routinely available for every individual, either healthy or affected. Clinical Genomics will move away from finding genetic defects to understanding pathophysiology and developing therapies for patients. As, unfortunately, the gene defect itself has only rarely enabled a direct therapy, this will require extensive studies in animal and human models. In addition, the knowledge on monogenic disorders paves the way to study the role of mitochondrial dysfunction in complex disorders, ranging from infertility, ageing and cancer to glaucoma and small fibre neuropathy.
Preventing the transmission of mitochondrial (and other) disease
Mitochondrial diseases can be caused by a defect in the nuclear or mitochondrial DNA (mtDNA). In addition to identifying the nuclear defect in the patient, WES-based preconception screening has been developed to prevent additionally the transmission of diseases of which the parents are both unknowingly carrier. Defects in the mtDNA are transmitted maternally with a fairly unpredictable clinical outcome. Our work has clarified the transmission of mtDNA and mtDNA-related disease in humans and zebrafish. We showed that the transmission of mtDNA disease can be prevented by prenatal diagnosis for cases with low recurrence risk (mostly de novo mutations), preimplantation genetic diagnosis for medium to high recurrence risk and mitochondrial replacement therapy (MRT, Newcastle) for very high recurrence risks. We were the first to demonstrate and explain positive and negative selection on pathogenic mtDNA mutations. To unravel underlying mechanisms, we determined in zebrafish the mitochondrial bottleneck, the mechanism of de novo mutations and the effect of a reduced mtDNA copy number on embryonic development.
Stem-cell based treatment of mitochondrial myopathy and LAMA2-RD
Although we were able, based on two gene defects identified, to develop a life-saving treatment (SLC19A3 – Thiamine, ACAD9 – Riboflavin) for fatal mitochondrial diseases, this is not the case for the majority of patients. Therefore we aim to develop a generic stem-cell-based strategy to treat myopathy of mtDNA patients, which is the symptom the generally suffer most from, and which can be extended to other muscle diseases as well. We will use autologous muscle stem-cells, called mesoangioblasts, which proliferate well in culture, can be injected in the blood stream and migrate out of the blood vessel to repair damaged muscle. Patients with the m.3243A>G mtDNA mutation in muscle have mesoangioblasts, which are largely mutation-free and ready to be used for therapy. We have established the IMPD and all the relevant SOPS and are currently executing a Phase I/II clinical trial to determine safety and (limitedly efficacy). We extend this approach to patients suffering from nuclear genetic muscle disease, more particularly LAMA2-RD, following CRISPR/Cas9 correction or compensation of the gene defect. This should recover both their LAMA2-related muscle problems and the mitochondrial deficiencies they are suffering from in their muscles.
Non primary mitochondrial disease
The availability of patient material with defects in many different mitochondrial pathways allows the study of the role of mitochondrial deficiencies in muscular dystrophies, like LAMA2-RD, and common disease and traits, like glaucoma, radiation induced lung toxicity, pain, and cognitive dysfunction, including 7T MRI. We combine iPSC technology to study tissue-specific manifestation in humans with zebrafish as a vertebrate model.
Societal impact
The societal impact of our work is high. The fact that we are able to find the genetic defect in the majority of patients with mitochondrial disease has an immense impact for this patient group. And we have taken it further. Every patient or carrier of a mitochondrial disease has a fair chance of having healthy children due to our work. Working at the edge of genetics and fertility raises ethical and societal concerns, and Bert Smeets as advisor of the prime regulatory board in the UK (HFEA) has contributed considerably to this discussion, also by invited presentations all over the world and participation in discussion groups. This attracted considerable attention of national and international media. The current work on treatment is being performed in close collaboration with patients and patient organizations, not only for mitochondrial myopathies, but for the broader group of muscle pathologies (www.generateyourmuscle.com). Patient advocacy organizations, like LAMA2-Europe and the Foundation "Voor Sara", are heavily involved as partners in our research fighting for the same cause. We as a research group explain and report on our work on scientific meetings, patient meetings and fund-raising events, bringing the progress of our work to our stakeholders and broader society. A spin-off company has been created to produce the stem cells as medicinal product.