Clinical and Neuroimaging Features in Two Children with Mutations in the Mitochondrial ND5 Gene

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.

Diagnosis of primary mitochondrial disorders -Emphasis on myopathological aspects

Mitochondrial disorders are one of the most common neurometabolic disorders affecting all age groups. The phenotype-genotype heterogeneity in these disorders can be attributed to the dual genetic control on mitochondrial functions, posing a challenge for diagnosis. Though the advancement in the high-throughput sequencing and other omics platforms resulted in a "genetics-first" approach, the muscle biopsy remains the benchmark in most of the mitochondrial disorders. This review focuses on the myopathological aspects of primary mitochondrial disorders. The utility of muscle biopsy is not limited to analyse the structural abnormalities; rather it also proves to be a potential tool to understand the deranged sub-cellular functions.

Neuroimaging of Mitochondrial Cytopathies

Mitochondrial diseases are a complex and heterogeneous group of genetic disorders that occur as a result of either nuclear DNA or mitochondrial DNA pathogenic variants, leading to a decrease in oxidative phosphorylation and cellular energy (ATP) production. Increasing knowledge about molecular, biochemical, and genetic abnormalities related to mitochondrial dysfunction has expanded the neuroimaging phenotypes of mitochondrial disorders. As a consequence of this growing field, the imaging recognition patterns of mitochondrial cytopathies are continually evolving. In this review, we describe the main neuroimaging characteristics of pediatric mitochondrial diseases, ranging from classical to more recent and challenging features. Due to the increased knowledge about the imaging findings of mitochondrial cytopathies, the pediatric neuroradiologist plays a crucial role in the diagnosis and evaluation of these patients.

Magnetic resonance imaging correlates of genetically characterized patients with mitochondrial disorders: A study from south India

BACKGROUND

Large studies analyzing magnetic resonance imaging correlates in different genotypes of mitochondrial disorders are far and few. This study sought to analyze the pattern of magnetic resonance imaging findings in a cohort of genetically characterized patients with mitochondrial disorders.

METHODS

The study cohort included 33 patients (age range 18 months-50 years, M:F - 0.9:1) with definite mitochondrial disorders seen over a period of 8 yrs. (2006-2013). Their MR imaging findings were analyzed retrospectively.

RESULTS

The patients were classified into three groups according to the genotype, Mitochondrial point mutations and deletions (n=21), SURF1 mutations (n=7) and POLG1 (n=5). The major findings included cerebellar atrophy (51.4%), cerebral atrophy (24.2%), signal changes in basal ganglia (45.7%), brainstem (34.2%) & white matter (18.1%) and stroke like lesions (25.7%). Spinal cord imaging showed signal changes in 4/6 patients. Analysis of the special sequences revealed, basal ganglia mineralization (7/22), lactate peak on magnetic resonance spectrometry (10/15), and diffusion restriction (6/22). Follow-up images in six patients showed that the findings are dynamic. Comparison of the magnetic resonance imaging findings in the three groups showed that cerebral atrophy and cerebellar atrophy, cortical signal changes and basal ganglia mineralization were seen mostly in patients with mitochondrial mutation. Brainstem signal changes with or without striatal lesions were characteristically noted in SURF1 group. There was no consistent imaging pattern in POLG1 group.

CONCLUSION

Magnetic resonance imaging findings in mitochondrial disorders are heterogeneous. Definite differences were noted in the frequency of anatomical involvement in the three groups. Familiarity with the imaging findings in different genotypes of mitochondrial disorders along with careful analysis of the family history, clinical presentation, biochemical findings, histochemical and structural analysis will help the physician for targeted metabolic and genetic testing.