Clinical Phenotype and Genetic Features of a Pair of Chinese Twins with Kearns-Sayre Syndrome

Mitochondrial encephalopathies and myopathies: Our tertiary center's experience

Mitochondrial diseases have a heterogeneous phenotype and can result from mutations in the mitochondrial or nuclear genomes, constituting a diagnostically and therapeutically challenging group of disorders. We report our center's experience with mitochondrial encephalopathies and myopathies with a cohort of 50 genetically and phenotypically diverse patients followed in the Neurology clinic over the last ten years. Seventeen patients had mitochondrial DNA mutations, presented over a wide range of ages with seizures, feeding difficulties, extraocular movements abnormalities, and had high rates of stroke-like episodes and regression. Twenty-seven patients had nuclear DNA mutations, presented early in life with feeding difficulty, failure-to-thrive, and seizures, and had high proportions of developmental delay, wheelchair dependence, spine abnormalities and dystonia. In six patients, a mutation could not be identified, but they were included for having mitochondrial disease confirmed by histopathology, enzyme analysis and clinical features. These patients had similar characteristics to patients with nuclear DNA mutations, suggesting missed underlying mutations in the nuclear genome. Management was variable among patients, but outcomes were universally poor with severe disability in all cases. Therapeutic entryways through elucidation of disease pathways and remaining unknown genes are acutely needed.

Electrolyte Disorders in Mitochondrial Cytopathies: A Systematic Review

SIGNIFICANCE STATEMENT

Several recent studies identified mitochondrial mutations in patients with Gitelman or Fanconi syndrome. Mitochondrial cytopathies are generally not considered in the diagnostic workup of patients with electrolyte disorders. In this systematic review, we investigated the presence of electrolyte disorders in patients with mitochondrial cytopathies to determine the relevance of mitochondrial mutation screening in this population. Our analysis demonstrates that electrolyte disorders are commonly reported in mitochondrial cytopathies, often as presenting symptoms. Consequently, more clinical attention should be raised for mitochondrial disease as cause for disturbances in electrolyte homeostasis. Further prospective cohort studies are required to determine the exact prevalence of electrolyte disorders in mitochondrial cytopathies.

BACKGROUND

Electrolyte reabsorption in the kidney has a high energy demand. Proximal and distal tubular epithelial cells have a high mitochondrial density for energy release. Recently, electrolyte disorders have been reported as the primary presentation of some mitochondrial cytopathies. However, the prevalence and the pathophysiology of electrolyte disturbances in mitochondrial disease are unknown. Therefore, we systematically investigated electrolyte disorders in patients with mitochondrial cytopathies.

METHODS

We searched PubMed, Embase, and Google Scholar for articles on genetically confirmed mitochondrial disease in patients for whom at least one electrolyte is reported. Patients with a known second genetic anomaly were excluded. We evaluated 214 case series and reports (362 patients) as well as nine observational studies. Joanna Briggs Institute criteria were used to evaluate the quality of included studies.

RESULTS

Of 362 reported patients, 289 had an electrolyte disorder, with it being the presenting or main symptom in 38 patients. The average number of different electrolyte abnormalities per patient ranged from 2.4 to 1.0, depending on genotype. Patients with mitochondrial DNA structural variants seemed most affected. Reported pathophysiologic mechanisms included renal tubulopathies and hormonal, gastrointestinal, and iatrogenic causes.

CONCLUSIONS

Mitochondrial diseases should be considered in the evaluation of unexplained electrolyte disorders. Furthermore, clinicians should be aware of electrolyte abnormalities in patients with mitochondrial disease.

Inherited causes of combined vision and hearing loss: clinical features and molecular genetics

Combined vision and hearing loss, also known as dual sensory impairment, can occur in several genetic conditions, including ciliopathies such as Usher and Bardet-Biedl syndrome, mitochondrial DNA disorders and systemic diseases, such as CHARGE, Stickler, Waardenburg, Alport and Alstrom syndrome. The retinal phenotype may point to the diagnosis of such disorders. Herein, we aim to provide a comprehensive review of the molecular genetics and clinical features of the most common non-chromosomal inherited disorders to cause dual sensory impairment.

Kearns-Sayre syndrome case. Novel 5,9 kb mtDNA deletion

BACKGROUND

Kearns-Sayre syndrome (KSS) is a rare multisystem mitochondrial disorder characterized by onset before 20 years of age and a typical clinical triad: progressive external ophthalmoplegia, pigmentary retinopathy and cardiac conduction anomalies. In most cases KSS is caused by spontaneous heteroplasmic single large-scale mitochondrial DNA (mtDNA) deletions. Long-range polymerase chain reaction (LR-PCR), next generation sequencing (NGS) and multiplex ligation-dependent probe amplification (MLPA) are the most widely applied methods for the identification of mtDNA deletions. Here, we report the case of 20-year-old male who presented with classic Kearns-Sayre syndrome, confirmed by novel 5,9 kb mtDNA deletion.

METHODS AND RESULTS

LR-PCR and MLPA methods were applied to identify the mitochondrial DNA deletion for the patient, but the results were conflicting. Molecular analysis using primer walking and Sanger sequencing identified a novel 5888 base pairs mtDNA deletion (NC_012920.1:m.6069_11956del) with CAAC nucleotides repeat sequence at the breakpoints.

CONCLUSION

Our study enriched the mtDNA variation spectrum associated with KSS and demonstrated the importance of choosing relevant molecular genetic methods.

Kearns–Sayre syndrome with a novel large-scale deletion: a case report

Background

Kearns–Sayre syndrome (KSS) is a rare, multisystem mitochondrial encephalomyopathy. We report a case of KSS with a novel 7.6-kb deletion as assessed through a long-range polymerase chain reaction (PCR) study in the blood. In addition, optical coherence tomography angiography (OCTA) confirmed deep retinal capillary atrophy for the first time.

Case presentation

A 13-year-old patient presented with progressive vision loss and difficulty with eye opening and was diagnosed with progressive external ophthalmoplegia and retinitis pigmentosa (RP). The patient also experienced heart block, vestibular dysfunction, growth retardation and multiple demyelinating lesions. A long-range PCR study in the blood revealed a large-scale Chrm: 6341–13,993 deletion, which was first reported and broadened the genetic spectrum of this disease. The patient underwent complete ophthalmic examination, medical history review and gene detection, resulting in a confirmation of the diagnosis of KSS. The patient was given a pair of applicable glasses to wear and was followed up every 3 months. An implantable pacemaker was also installed based on the advice of the physician.

Conclusions

We reported a novel large-scale deletion in the mitochondrial DNA of KSS, and OCTA was used for the first time to confirm deep retinal capillary atrophy. Furthermore, because ophthalmic symptoms are often the primary manifestation of KSS, the relationship between ophthalmology and mitochondrial diseases should be emphasised.