Mitochondrial cytopathies can have kidney involvement in up to half of cases. Their diagnosis is challenging due to phenotypic variability, lack of noninvasive tests to assess mitochondrial dysfunction, and genetic heterogeneity. We report on a young adult male with hypertrophic cardiomyopathy (HCM) and chronic kidney disease (CKD) with subnephrotic proteinuria who presented to the emergency department with kidney failure and hypervolemia requiring dialysis. A kidney biopsy showed focal segmental and global glomerulosclerosis, extensive foot process effacement, and abnormal mitochondria in podocytes and tubular epithelial cells; the genetic workup identified a rare FASTKD2 exon 2 variant, c.29G>C p.(Ser10Thr), in homozygosity; and functional mitochondrial assays in cultured skin fibroblasts showed reduction in FASTKD2 protein expression and moderate combined impairment in mitochondrial respiratory chain (MRC) assembly and function. This is the first report of a FASTKD2-associated cardiorenal mitochondrial cytopathy, characterized by young adult-onset proteinuric CKD and dilated HCM, in the absence of the severe neurologic manifestations described in patients with biallelic FASTKD2 variants. We hypothesize that the increased production of reactive oxygen species associated with moderate MRC impairment could result in a smoldering podocytopathy with progressive proteinuric CKD, without overt tubulopathy or encephalomyopathy-which might be, instead, pathogenically related to adenosine triphosphate deficiency.

Bilateral lower extremity weakness and swelling can have several causes. Although often underdiagnosed, mitochondrial myopathy is more prevalent in the general population than more commonly suspected diseases, such as Guillain-Barre syndrome. The clinical manifestations of mitochondrial disease can be broadly classified into 3 categories: chronic progressive external ophthalmoplegia, skeletal muscle-central nervous system syndromes, or pure myopathy. Cardiac abnormalities occur in 30% to 32% of cases, mostly in the form of hypertrophic cardiomyopathy, dilated cardiomyopathy, or conduction abnormalities. We report a case of a 21-year-old student who developed bilateral lower limb weakness, pain, and swelling diagnosed with mitochondrial myopathy on muscle biopsy. Initial laboratory tests revealed elevated creatinine kinase, brain natriuretic peptide, troponin, myoglobin, and lactic acid and reduced serum bicarbonate. Cardiac workup revealed systolic heart failure with a reduced ejection fraction. Endomyocardial biopsy revealed punctate foci of lymphocytic myocarditis. However, cardiac magnetic resonance imaging did not reveal either myocarditis or an infiltrative cardiac disease. An extensive autoimmune and infection work-up was negative. A muscle biopsy from the patient's rectus femoris revealed scattered ragged-blue fibers (stained with NADH dehydrogenase), scattered ragged-red fibers on modified Gomori trichrome stain, and cytochrome-c oxidase negative fibers with increased perimysial and endomysial connective tissue, consistent with active and chronic primary mitochondrial myopathy. The patient was treated successfully with furosemide, metoprolol, and methylprednisolone. Adult-onset mitochondrial myopathy is a rare clinical disorder, and our experience stresses the importance of using an inter-disciplinary team approach to diagnose uncommon clinical disorders with widely variable multisystem involvement.

Chronic progressive external ophthalmoplegia (CPEO) is symptom complex with progressive ptosis and restricted ocular motility without diplopia. MYH2 myopathy is rare disorder presenting with CPEO and muscle weakness. We report two Indian patients of MYH2 myopathy with unique features. Patient-1 presented with early adult-onset esophageal reflux followed by, proximal lower limb weakness, proptosis, CPEO without ptosis. He had elevated creatine kinase along with characteristic muscle MRI findings of prominent semitendinosus and medial gastrocnemius involvement. Patient -2 presented with early adult onset CPEO without limb weakness. His creatine kinase was normal. Both the patients had novel MYH2 mutations: a homozygous 5'splice variation in intron 4 (c.348 + 2dup) in patient 1 and homozygous single base pair deletion in exon 32 (p. Ala1480ProfsTer11) in patient 2. Unique features noted include adult onset, isolated CPEO, proptosis, esophageal reflux disease and absence of skeletal abnormalities. MYH2 myopathy has to be considered in adult patients with CPEO.

We report a case of adult-onset dystonia presenting with chronic progressive external ophthalmoplegia. The patient had ptosis in both eyes, particularly the left eye, for no obvious reason since the age of 10, which was progressively aggravated. The clinical diagnosis was chronic progressive external ophthalmoplegia. However, whole gene sequencing revealed the mitochondrial A3796G missense mutation, so the patient was clearly diagnosed as adult-onset dystonia and given treatment to reduce blood glucose and improve muscle metabolism. The A3796G mutation in the ND1 subunit of the mitochondrial complex leading to ophthalmoplegia is relatively rare, requiring a combination with genetic testing for confirmation of diagnosis. 1例表现为慢性进行性眼外肌麻痹（CEPO）的成人发病型肌张力障碍患者就诊于内分泌科，患者既往自10岁起无明显诱因出现双侧上眼睑下垂，左眼为著，并呈进行性加重，临床诊断CEPO，但行线粒体全基因测序发现A3796G错义突变，故明确诊断为成人发病型肌张力障碍，予以降糖及改善肌代谢治疗。线粒体复合体ND1亚基的A3796G突变导致“眼睑痉挛”肌张力障碍者较为少见，需结合基因检测明确诊断，故临床医生应提高对该疾病的重视。.

Mitochondrial DNA (mtDNA) maintenance disorders embrace a broad range of clinical syndromes distinguished by the evidence of mtDNA depletion and/or deletions in affected tissues. Among the nuclear genes associated with mtDNA maintenance disorders, RNASEH1 mutations produce a homogeneous phenotype, with progressive external ophthalmoplegia (PEO), ptosis, limb weakness, cerebellar ataxia, and dysphagia. The encoded enzyme, ribonuclease H1, is involved in mtDNA replication, whose impairment leads to an increase in replication intermediates resulting from mtDNA replication slowdown. Here, we describe two unrelated Italian probands (Patient 1 and Patient 2) affected by chronic PEO, ptosis, and muscle weakness. Cerebellar features and severe dysphagia requiring enteral feeding were observed in one patient. In both cases, muscle biopsy revealed diffuse mitochondrial abnormalities and multiple mtDNA deletions. A targeted next-generation sequencing analysis revealed the homozygous RNASEH1 mutations c.129-3C>G and c.424G>A in patients 1 and 2, respectively. The c.129-3C>G substitution has never been described as disease-related and resulted in the loss of exon 2 in Patient 1 muscle RNASEH1 transcript. Overall, we recommend implementing the use of high-throughput sequencing approaches in the clinical setting to reach genetic diagnosis in case of suspected presentations with impaired mtDNA homeostasis.