MPV17 hepatocerebral mitochondrial DNA depletion syndrome presenting as acute flaccid paralysis - A case report

Clinical and genetic spectrum of Mitochondrial DNA depletion syndromes: a report of 6 cases with 4 novel variants

Mitochondrial DNA (mtDNA) depletion syndromes (MDS) are a heterogeneous group of rare autosomal recessive genetic disorders characterized by a decrease in the number of mtDNA copies inside the organ involved. There are three distinct forms of MDS including the hepatocerebral, the myopathic and the encephalomyopathic forms. The diversity in the clinical and genetic spectrum of these disorders makes the diagnosis challenging. Here, we describe the clinical phenotype and the genetic spectrum of 6 patients with MDS including 4 novel variants and compare them with previously reported cases. Subject and Methods Six patients from six unrelated families were included in this study. All the patients were subjected to a detailed history, thorough general and neurologic examination, basic laboratory investigations including lactic acid and ammonia, amino acids, acylcarnitine profiles and brain MRI. Whole-exome sequencing was performed for all of them to confirm the suspicion of mitochondrial disorder. RESULTS: In our series, four patients presented with the hepatocerebral form of MDS with the major presenting manifestation of progressive liver cell failure with severe hypotonia and global developmental delay. Four variants in the DGUOK gene and the MPV17 have been identified including 2 novel variants. One patient was identified in the myopathic form presenting with myopathy associated with two novel variants in the TK2 gene. One patient was diagnosed with encephalomyopathic form presenting with persistent lactic acidosis and global delay due to a homozygous variant in the FBXL4 gene. CONCLUSION: MDS has a wide spectrum of heterogeneous clinical presentations and about nine different genes involved. Whole exome sequencing (WES) has resulted in faster diagnosis of these challenging cases as the phenotype overlap with many other disorders. This should be considered the first-tier diagnostic test obviating the need for more invasive testing like muscle biopsies.

Mitochondrial diseases in South Asia - A systematic review

BACKGROUND

Mitochondrial diseases are largely underdiagnosed due to their heterogeneity in clinical presentation and genotype. This is especially true for resource-constrained settings in South Asian countries such as Afghanistan, Bangladesh, Bhutan, India, Maldives, Pakistan, Nepal, Sri Lanka and Myanmar. This study aims to evaluate the current status of clinical presentations, diagnosis and treatment of Mitochondrial diseases in the South Asian region.

METHODS

We undertook a systematic review of the literature on mitochondrial diseases in the South Asian region. We searched Medline, Pubmed, Cochrane library, and Google scholar using the search terms, "Mitochondrial diseases" AND "Metabolic diseases" (Mesh terms) in the title or the abstract field for each South Asian Country (Afghanistan, Bangladesh, Bhutan, India, Maldives, Pakistan, Nepal, Sri Lanka and Myanmar).

RESULTS

We found 89 citations in Pubmed, 22 citations in Cochrane library and 68 in Google scholar respectively. A total of 25 non-duplicated studies met the inclusion and exclusion criteria. After assessing the quality of the published studies 18 were included. Which comprised of 17 case reports and one case-control study.

CONCLUSION

Studies that were published were case reports from India, Pakistan, and Sri Lanka. Due to the paucity of published data on mitochondrial diseases in the South Asian region, it is difficult to estimate its true burden.

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.

Cerebral imaging in paediatric mitochondrial disorders

OBJECTIVES

Because the central nervous system (CNS) is the second most frequently affected organ in mitochondrial disorders (MIDs) and since paediatric MIDs are increasingly recognised, it is important to know about the morphological CNS abnormalities on imaging in these patients. This review aims at summarising and discussing current knowledge and recent advances concerning CNS imaging abnormalities in paediatric MIDs.

METHODS

A systematic literature review was conducted.

RESULTS

The most relevant CNS abnormalities in paediatric MIDs on imaging include white and grey matter lesions, stroke-like lesions as the morphological equivalent of stroke-like episodes, cerebral atrophy, calcifications, optic atrophy, and lactacidosis. Because these CNS lesions may be seen with or without clinical manifestations, it is important to screen all MID patients for cerebral involvement. Some of these lesions may remain unchanged for years whereas others may be dynamic, either in the sense of progression or regression. Typical dynamic lesions are stroke-like lesions and grey matter lesions. Clinically relevant imaging techniques for visualisation of CNS abnormalities in paediatric MIDs are computed tomography, magnetic resonance (MR) imaging, MR spectroscopy, single-photon emission computed tomography, positron-emission tomography, and angiography.

CONCLUSIONS

CNS imaging in paediatric MIDs is important for diagnosing and monitoring CNS involvement. It also contributes to the understanding of the underlying pathomechanisms that lead to CNS involvement in MIDs.