Mitochondrial multiorgan disorder syndrome score generated from definite mitochondrial disorders

The Novel Role of PGC1α in Bone Metabolism

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) is a protein that promotes transcription of numerous genes, particularly those responsible for the regulation of mitochondrial biogenesis. Evidence for a key role of PGC1α in bone metabolism is very recent. In vivo studies showed that PGC1α deletion negatively affects cortical thickness, trabecular organization and resistance to flexion, resulting in increased risk of fracture. Furthermore, in a mouse model of bone disease, PGC1α activation stimulates osteoblastic gene expression and inhibits atrogene transcription. PGC1α overexpression positively affects the activity of Sirtuin 3, a mitochondrial nicotinammide adenina dinucleotide (NAD)-dependent deacetylase, on osteoblastic differentiation. In vitro, PGC1α overexpression prevents the reduction of mitochondrial density, membrane potential and alkaline phosphatase activity caused by Sirtuin 3 knockdown in osteoblasts. Moreover, PGC1α influences the commitment of skeletal stem cells towards an osteogenic lineage, while negatively affects marrow adipose tissue accumulation. In this review, we will focus on recent findings about PGC1α action on bone metabolism, in vivo and in vitro, and in pathologies that cause bone loss, such as osteoporosis and type 2 diabetes.

Genetic ataxias: update on classification and diagnostic approaches

Ataxia encompasses a large group of rare disorders characterized by irregular movements, decreased coordination, imbalance, kinetic tremor, wide-based stance, and dysarthria. Evaluating ataxia can be challenging considering the volume of disorders and their complex pathologies involving diverse genetic and clinical factors. This is a comprehensive review of the genetic ataxia literature, presenting updated guidelines for differential diagnosis. Age, time course, and family history provide initial guidance for evaluation of ataxia. As genetic testing is increasingly utilized, new genes are discovered and phenotypes for existing disorders are expanded. This review assists physicians by offering a diagnostic roadmap for suspected hereditary ataxia based on the current literature.

Variant m.1555A>G in MT-RNR1 causes hearing loss and multiorgan mitochondrial disorder

BACKGROUND

Mitochondrial disorders (MIDs) are usually multisystem disorders, affecting not only a single organ/tissue but also progressively more than one.

METHODS

Letter to the Editor.

RESULTS

Though phenotypic manifestations of the m.1555A>G mutation are usually mono-organic, there are indications that short stature, osteoporosis, arterial hypertension, and recurrent headache can be also a manifestation of this variant.MID patients with apparently single organ involvement need to be prospectively investigated for multisystem disease, as multisystem manifestations can be subtle or even subclinical.Concerning the phenotypic expression of the m.1555A>G variant it is crucial to know the heteroplasmy rates in various tissues, as they may strongly contribute to the phenotypic expression of the disease. Maternal transmission can be confirmed by running a basic local alignment search tool.

CONCLUSIONS

The m.1555A>G variant is not only associated with hearing loss but with a number of other multiorgan manifestations. Heteroplasmy rate are required for establishing a genotype/phenotype correlation.

MELAS Missed for Years: Stroke-Like Lesions Are No Indication for Brain Biopsy

A 56-year-old female with a history of chronic alcoholism until age 38 y with a relapse between ages 45 and 46 y developed seizures, psychosis, and hemianopia to the left at age 46 y. Imaging revealed a right parieto-occipital lesion with intralesional bleeding. Five months after the first lesion she developed a second left parieto-occipital lesion, resulting in cortical blindness. Extensive workup, including brain biopsy, was noninformative. Retrospectively, the occipital abnormalities were identified as stroke-like lesions (SLLs). Further manifestations of the mitochondrial disorder (MID) were tremor, cerebral atrophy, bilateral basal ganglia, calcification, glaucoma, hypoacusis, short stature, hyperostosis frontalis, hyperthyroidism, sick-sinus syndrome and AV-block-1, and myopathy. According to the Walker criteria, a possible MID was diagnosed. In conclusion, adult-onset MID may be missed for years, SLLs may be easily misinterpreted entailing brain biopsy, and psychosis may contribute to a reduced impact for proper workup of a MID.

Aortic root ectasia as a phenotypic feature of a mitochondrial disorder

Mitochondrial disorder (MID) can be suspected upon application of the mitochondrial multiorgan disorder syndrome score; aortic root ectasia (ARE) can be a phenotypic feature of MIDs; ARE in a MID may result from affection of vascular smooth muscle cells by the metabolic defect; ARE requires long-term follow-up not to miss the point at which ARE transforms to an aneurysm requiring vascular surgery.

Biomarkers for Detecting Mitochondrial Disorders

(1) Objectives: Mitochondrial disorders (MIDs) are a genetically and phenotypically heterogeneous group of slowly or rapidly progressive disorders with onset from birth to senescence. Because of their variegated clinical presentation, MIDs are difficult to diagnose and are frequently missed in their early and late stages. This is why there is a need to provide biomarkers, which can be easily obtained in the case of suspecting a MID to initiate the further diagnostic work-up. (2) Methods: Literature review. (3) Results: Biomarkers for diagnostic purposes are used to confirm a suspected diagnosis and to facilitate and speed up the diagnostic work-up. For diagnosing MIDs, a number of dry and wet biomarkers have been proposed. Dry biomarkers for MIDs include the history and clinical neurological exam and structural and functional imaging studies of the brain, muscle, or myocardium by ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), MR-spectroscopy (MRS), positron emission tomography (PET), or functional MRI. Wet biomarkers from blood, urine, saliva, or cerebrospinal fluid (CSF) for diagnosing MIDs include lactate, creatine-kinase, pyruvate, organic acids, amino acids, carnitines, oxidative stress markers, and circulating cytokines. The role of microRNAs, cutaneous respirometry, biopsy, exercise tests, and small molecule reporters as possible biomarkers is unsolved. (4) Conclusions: The disadvantages of most putative biomarkers for MIDs are that they hardly meet the criteria for being acceptable as a biomarker (missing longitudinal studies, not validated, not easily feasible, not cheap, not ubiquitously available) and that not all MIDs manifest in the brain, muscle, or myocardium. There is currently a lack of validated biomarkers for diagnosing MIDs.