Lack of founder effect for an identical mtDNA depletion syndrome (MDS)-associated MPV17 mutation shared by Navajos and Italians

Outcomes after liver transplantation in MPV17 deficiency (Navajo neurohepatopathy): A single-center case series

BACKGROUND

MPV17-related mitochondrial DNA maintenance defect (MPV17 deficiency) is a rare, autosomal recessive mitochondrial DNA depletion syndrome with a high mortality rate in infancy and early childhood due to progression to liver failure. Liver transplantation for children with MPV17 deficiency has been considered controversial due to uncertainty about the potential progression of extrahepatic manifestations following liver transplantation.

METHODS

We describe our institution's experience for two infants diagnosed with infantile MPV17 deficiency who presented in acute on chronic liver failure, but with normal development and normal neurological status who successfully underwent liver transplantation.

RESULTS

Both patients underwent successful liver transplantation with normal development and neurological status at 3 years and 16 months post-transplant, respectively.

CONCLUSIONS

In this rare disease population, we describe two infants with MPV17 deficiency who underwent liver transplantation for acute on chronic liver failure who continue to have normal development, without progression of neurological disease. MPV17 deficiency should not be considered a contraindication to liver transplantation.

Loss of mpv17 affected early embryonic development via mitochondria dysfunction in zebrafish

MVP17 encodes a mitochondrial inner-membrane protein, and mutation of human MVP17 can cause mitochondria DNA depletion syndrome (MDDS). However, the underlying function of mpv17 is still elusive. Here, we developed a new mutant with mpv17 knockout by using the CRISPR/Cas9 system. The mpv17^-/- zebrafish showed developmental defects in muscles, liver, and energy supply. The mpv17^-/- larvae hardly survived beyond a month, and they showed abnormal growth during the development stage. Abnormal swimming ability was also found in the mpv17^-/- zebrafish. The transmission electron microscope (TEM) observation indicated that the mpv17^-/- zebrafish underwent severe mitochondria dysfunction and the disorder of mitochondrial cristae. As an energy producer, the defects of mitochondria significantly reduced ATP content in mpv17^-/- zebrafish, compared to wild-type zebrafish. We hypothesized that the disorder of mitochondria cristae was contributed to the dysfunction of muscle and liver in the mpv17^-/- zebrafish. Moreover, the content of major energy depot triglycerides (TAG) was decreased dramatically. Interestingly, after rescued with normal exogenous mitochondria by microinjection, the genes involved in the TAG metabolism pathway were recovered to a normal level. Taken together, this is the first report of developmental defects in muscles, liver, and energy supply via mitochondria dysfunction, and reveals the functional mechanism of mpv17 in zebrafish.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: anthropological, medical, and scientific aspects

The peopling of the Americas by Native Americans occurred in 4 waves of which the last was Nadene language speakers of whom Athabaskans are the largest group. As the Europeans were entering the Southwestern states of the USA, Athabaskan hunting-gathering tribes were migrating South from Canada along the Rocky Mountains and undergoing potential bottlenecks reflected in autosomal recessive diseases shared by Apaches and Navajos. About 300 years ago, the Navajo developing a sedentary culture learned from Pueblo Indians while the Apache remained hunter-gathers. Although most of the tribe was rounded up and forced to relocate to Bosque Redondo, the adult breeding population was large enough to prevent a genetic bottleneck. However, some Navajo underwent further population bottlenecks while hiding from the brutal US Army action (under Kit Carson’s guidance). This led to an increased frequency of other autosomal recessive diseases. Recent advances in population genetics, pathophysiology of the diseases, and social/ethical issues concerning their study are reviewed.

Weaving the Strands of Life (Iiná Bitł'ool): History of Genetic Research Involving Navajo People

To date, some genetic studies offer medical benefits but lack a clear pathway to benefit for people from underrepresented backgrounds. Historically, Indigenous people, including the Diné (Navajo people), have raised concerns about the lack of benefits, misuse of DNA samples, lack of consultation, and ignoring of cultural and traditional ways of knowing. Shortly after the Navajo Nation Human Research Review Board was established in 1996, the Navajo Nation recognized growing concerns about genetic research, and in 2002 they established a moratorium on human genetic research studies. The moratorium effectively has protected their citizens from potential genetic research harms. Despite the placement of the moratorium, some genetic research studies have continued using blood and DNA samples from Navajo people. To understand the history of genetic research involving Navajo people, the authors conducted a literature review of genetic or genetics-related research publications that involved Navajo people, identifying 79 articles from the years 1926 to 2018. To their knowledge, no known literature review has comprehensively examined the history of genetic research in the Navajo community. This review divides the genetic research articles into the following general classifications: bacteria or virus genetics, blood and human leukocyte antigens, complex diseases, forensics, hereditary diseases, and population genetics and migration. The authors evaluated the methods reported in each article, described the number of Navajo individuals reported, recorded the academic and tribal approval statements, and noted whether the study considered Diné cultural values. Several studies focused on severe combined immunodeficiency disease, population history, neuropathy, albinism, and eye and skin disorders that affect Navajo people. The authors contextualize Diné ways of knowing related to genetics and health with Western scientific concepts to acknowledge the complex philosophy and belief system that guides Diné people and recognizes Indigenous science. They also encourage researchers to consider cultural perspectives and traditional knowledge that has the potential to create stronger conclusions and better-informed, ethical, and respectful science.

Mitochondrial dysfunction and its role in tissue-specific cellular stress

Mitochondrial bioenergetics require the coordination of two different and independent genomes. Mutations in either genome will affect mitochondrial functionality and produce different sources of cellular stress. Depending on the kind of defect and stress, different tissues and organs will be affected, leading to diverse pathological conditions. There is no curative therapy for mitochondrial diseases, nevertheless, there are strategies described that fight the various stress forms caused by the malfunctioning organelles. Here, we will revise the main kinds of stress generated by mutations in mitochondrial genes and outline several ways of fighting this stress.

Missing mitochondrial Mpv17 gene function induces tissue-specific cell-death pathway in the degenerating inner ear

The Mpv17 gene encodes a mitochondrial inner-membrane protein that has been implicated in the metabolism of reactive oxygen species. The loss of function in Mpv17-/- mice leads to early sensorineural deafness associated with severe inner ear degeneration and late onset of kidney failure. The present study demonstrates that the onset of the degeneration of the cochlear neuroepithelia is related to the onset of auditory function and appears to be first restricted to the outer hair cells (OHC), which subsequently undergo rapid degeneration. At the age of 18 days, the OHC lateral membrane degenerates and extensive vacuolization of the cytoplasm is followed by lysis of the OHCs. Such degenerative processes have been seen for the first time in relation to auditory dysfunction. The structural degeneration pattern of the OHC appears to be similar to the described paraptotic processes (an alternative form of programmed cell death) discussed in the literature as a cause of cytoplasmic neurodegeneration. In contrast, the melanocyte-like intermediate cells that are of neural crest origin and that are located in the stria vascularis, undergo apoptosis, as documented ultrastructurally. A lack of Mpv17 protein function in mitochondria thus seems to initiate tissue-specific cell-death pathways resulting in the pathology seen during the degeneration process.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: recent advances and implications for the future

Genetic and linguistic data suggest that the Na-Dene, of which the Athabaskans are the largest group, are part of a later immigration into the Americas than the first Amerind immigration. Whether a second and third immigration can be separated seems unlikely but continued cross-Bering Strait exchanges may have masked what was a greater separation in the past. The movement of tribes into Siberia appears to have involved a genetic bottleneck leading to at least one disease allele shared by Eskimo/Aleuts and Navajos and a second possibly shared by the Navajo and a Siberian population, but not the same Siberian population that share deep linguistic affinities with the Navajo. A second bottleneck appears to have occurred with the migration of Athabaskans from Northwest North America to the Southwestern United States along the Rocky Mountains. This bottleneck is reflected in several rare recessive diseases shared by the Navajo and Apache. Finally, the Navajo were captured and imprisoned under conditions which led to severe population loss. This, and the "hiding away" of a small number of Navajos in what is now the Western portion of the reservation, led to a Navajo-specific bottleneck(s) resulting in an increased frequency of several rare recessive diseases among the Navajo. Prejudice against human genetic research is high among the Southwestern Athabaskans but attempts to bridge the gap are now occurring. The involvement of Navajo scientists in this process is especially encouraging.

Clinical and molecular features of mitochondrial DNA depletion syndromes

Mitochondrial DNA depletion syndromes (MDSs) form a group of autosomal recessive disorders characterized by profoundly decreased mitochondrial DNA copy numbers in affected tissues. Three main clinical presentations are known: myopathic, encephalomyopathic and hepatocerebral. The first is associated with mutations in thymidine kinase 2 (TK2) and p53-induced ribonucleotide reductase B subunit (RRM2B); the second with mutations in succinate synthase A (SUCLA2) and B (SUCLG1); the third with mutations in Twinkle (PEO1), pol-gammaA (POLG1), deoxyguanosine kinase (DGUOK) and MPV17 (MPV17). In this work, we review the MDS-associated phenotypes and present our own experience of 32 MDS patients, with the aim of defining the mutation frequency of the known genes, the clinical spectrum of the diseases, and the genotype-phenotype correlations. Five of our patients carried previously unreported mutations in one of the eight MDS genes.

Disorders from perturbations of nuclear-mitochondrial intergenomic cross-talk

In the course of evolution, mitochondria lost their independence, and mitochondrial DNA (mtDNA) became the 'slave' of nuclear DNA, depending on numerous nucleus-encoded factors for its integrity, replication and expression. Mutations in any of these factors may alter the cross-talk between the two genomes and cause Mendelian disorders characterized by qualitative (multiple deletions) or quantitative (depletion) alterations of mtDNA, or by defective translation of mtDNA-encoded respiratory chain components.

Mitochondrial diseases: a cross-talk between mitochondrial and nuclear genomes

More than one billion years ago, mitochondria were free-living prokaryotic organisms with their own DNA. However, during the evolution, ancestral genes have been transferred from the mitochondrial to the nuclear genome so that mtDNA became dependent on numerous nucleus-encoded factors for its integrity, replication and expression. Mutations in any of these factors may alter the cross-talk between the two genomes and cause Mendelian diseases that affect mtDNA integrity or expression.

Early-onset liver mtDNA depletion and late-onset proteinuric nephropathy in Mpv17 knockout mice

In humans, MPV17 mutations are responsible for severe mitochondrial depletion syndrome, mainly affecting the liver and the nervous system. To gain insight into physiopathology of MPV17-related disease, we investigated an available Mpv17 knockout animal model. We found severe mtDNA depletion in liver and, albeit to a lesser extent, in skeletal muscle, whereas hardly any depletion was detected in brain and kidney, up to 1 year after birth. Mouse embryonic fibroblasts did show mtDNA depletion, but only after several culturing passages, or in a serumless culturing medium. In spite of severe mtDNA depletion, only moderate decrease in respiratory chain enzymatic activities, and mild cytoarchitectural alterations, were observed in the Mpv17^−/− livers, but neither cirrhosis nor failure ever occurred in this organ at any age. The mtDNA transcription rate was markedly increased in liver, which could contribute to compensate the severe mtDNA depletion. This phenomenon was associated with specific downregulation of Mterf1, a negative modulator of mtDNA transcription. The most relevant clinical features involved skin, inner ear and kidney. The coat of the Mpv17^−/− mice turned gray early in adulthood, and 18-month or older mice developed focal segmental glomerulosclerosis (FSGS) with massive proteinuria. Concomitant degeneration of cochlear sensory epithelia was reported as well. These symptoms were associated with significantly shorter lifespan. Coincidental with the onset of FSGS, there was hardly any mtDNA left in the glomerular tufts. These results demonstrate that Mpv17 controls mtDNA copy number by a highly tissue- and possibly cytotype-specific mechanism.