A case of Kearns-Sayre syndrome showing a constant proportion of deleted mitochondrial DNA in blood cells during 6 years of follow-up

Adrenal Dysfunction in Mitochondrial Diseases

Cortisol is central to several homeostatic mechanisms including the stress and immune response. Adrenal insufficiency and impaired cortisol production leads to severe, potentially fatal disorders. Several fundamental stages of steroidogenesis occur within the mitochondria. These dynamic organelles not only contribute ATP for steroidogenesis, but also detoxify harmful by-products generated during cortisol synthesis (reactive oxygen species). Mutations in nuclear or mitochondrial DNA that impair mitochondrial function lead to debilitating multi-system diseases. Recently, genetic variants that impair mitochondrial function have been identified in people with isolated cortisol insufficiency. This review aimed to clarify the association between mitochondrial diseases and adrenal insufficiency to produce cortisol. Mitochondrial diseases are rare and mitochondrial diseases that feature adrenal insufficiency are even rarer. We identified only 14 cases of adrenal insufficiency in people with confirmed mitochondrial diseases globally. In line with previous reviews, adrenal dysfunction was most prevalent in mitochondrial deletion syndromes (particularly Pearson syndrome and Kearns-Sayre syndrome) and with point mutations that compromised oxidative phosphorylation. Although adrenal insufficiency has been reported with mitochondrial diseases, the incidence reflects that expected in the general population. Thus, it is unlikely that mitochondrial mutations alone are responsible for an insufficiency to produce cortisol. More research is needed into the pathogenesis of adrenal disease in these individuals.

MITOL dysfunction causes dwarfism with anterior pituitary hypoplasia

In mitochondrial disorders, short stature and growth failure are common symptoms, but their underlying mechanism remains unknown. In this study, we examined the cause of growth failure of mice induced by nestin promoter-driven knockout of the mitochondrial ubiquitin ligase MITOL (MARCH5), a key regulator of mitochondrial function. MITOL-knockout mice have congenital hypoplasia of the anterior pituitary caused by decreased expression of pituitary transcript factor 1 (Pit1). Consistently, both mRNA levels of growth hormone (GH) and prolactin levels were markedly decreased in the anterior pituitary of mutant mice. Growth failure of mutant mice was partly rescued by hypodermic injection of recombinant GH. To clarify whether this abnormality was induced by the primary effect of MITOL knockdown in the anterior pituitary or a secondary effect of other lesions, we performed lentiviral-mediated knockdown of MITOL on cultured rat pituitary GH3 cells, which secrete GH. GH production was severely compromised in MITOL-knockdown GH3 cells. In conclusion, MITOL plays a critical role in the development of the anterior pituitary; therefore, mice with MITOL dysfunction exhibited pituitary dwarfism caused by anterior pituitary hypoplasia. Our findings suggest that mitochondrial dysfunction is commonly involved in the unknown pathogenesis of pituitary dwarfism.

Potentially diagnostic electron paramagnetic resonance spectra elucidate the underlying mechanism of mitochondrial dysfunction in the deoxyguanosine kinase deficient rat model of a genetic mitochondrial DNA depletion syndrome

A novel rat model for a well-characterized human mitochondrial disease, mitochondrial DNA depletion syndrome with associated deoxyguanosine kinase (DGUOK) deficiency, is described. The rat model recapitulates the pathologic and biochemical signatures of the human disease. The application of electron paramagnetic (spin) resonance (EPR) spectroscopy to the identification and characterization of respiratory chain abnormalities in the mitochondria from freshly frozen tissue of the mitochondrial disease model rat is introduced. EPR is shown to be a sensitive technique for detecting mitochondrial functional abnormalities in situ and, here, is particularly useful in characterizing the redox state changes and oxidative stress that can result from depressed expression and/or diminished specific activity of the distinct respiratory chain complexes. As EPR requires no sample preparation or non-physiological reagents, it provides information on the status of the mitochondrion as it was in the functioning state. On its own, this information is of use in identifying respiratory chain dysfunction; in conjunction with other techniques, the information from EPR shows how the respiratory chain is affected at the molecular level by the dysfunction. It is proposed that EPR has a role in mechanistic pathophysiological studies of mitochondrial disease and could be used to study the impact of new treatment modalities or as an additional diagnostic tool.

Endocrine disorders in mitochondrial disease

Endocrine dysfunction in mitochondrial disease is commonplace, but predominantly restricted to disease of the endocrine pancreas resulting in diabetes mellitus. Other endocrine manifestations occur, but are relatively rare by comparison. In mitochondrial disease, neuromuscular symptoms often dominate the clinical phenotype, but it is of paramount importance to appreciate the multi-system nature of the disease, of which endocrine dysfunction may be a part. The numerous phenotypes attributable to pathogenic mutations in both the mitochondrial (mtDNA) and nuclear DNA creates a complex and heterogeneous catalogue of disease which can be difficult to navigate for novices and experts alike. In this article we provide an overview of the endocrine disorders associated with mitochondrial disease, the way in which the underlying mitochondrial disorder influences the clinical presentation, and how these factors influence subsequent management.

Phylogenetic analysis of mitochondrial DNA in a patient with Kearns-Sayre syndrome containing a novel 7629-bp deletion

Mitochondrial DNA mutations have been associated with different illnesses in humans, such as Kearns-Sayre syndrome (KSS), which is related to deletions of different sizes and positions among patients. Here, we report a Mexican patient with typical features of KSS containing a novel deletion of 7629 bp in size with 85% heteroplasmy, which has not been previously reported. Sequence analysis revealed 3-bp perfect short direct repeats flanking the deletion region, in addition to 7-bp imperfect direct repeats within 9-10 bp. Furthermore, sequencing, alignment and phylogenetic analysis of the hypervariable region revealed that the patient may belong to a founder Native American haplogroup C4c.

Juvenile cobalamin deficiency in a 17-year-old child with autonomic dysfunction and skin changes

We report a rare case of juvenile cobalamin deficiency who presented at the age of 17 years. He was underweight and had skin changes, normocytic anemia, and autonomic dysfunction, which led to adynamic ileus and acute postrenal failure. The expected macrocytosis was masked by an underlying alpha-thalassemia trait. The patient had an excellent response to parenteral cobalamin treatment.

A case of Kearns-Sayre syndrome with two novel deletions (9.768 and 7.253 kb) of the mtDNA associated with the common deletion in blood leukocytes, buccal mucosa and hair follicles

Kearns-Sayre syndrome is a mitochondrial disorder characterized by the emergence before the age of 20 years of progressive external ophthalmoplegia, pigmentary retinopathy, with other heterogeneous clinical manifestations. Generally, mitochondrial DNA deletions were associated with KSS but the size and position of these deletions differ among patients. This study reported a Tunisian patient with typical features of KSS. Long-range PCR amplification of the mtDNA in different tissues from this patient showed multiple mitochondrial deletions: two novel 9.768 and 7.253 kb deletions spanning respectively nucleotides 6124-15,893 and 8572-15,826 associated with the common 4.977 kb deletion.

Hematological manifestations of primary mitochondrial disorders

At onset mitochondrial disorders (MID) frequently manifest as a mono-organic problem but turn into multisystem disease during the disease course in most of the cases. Organs/tissues most frequently affected in MID are the cerebrum, peripheral nerves, and the skeletal muscle. Additionally, most of the inner organs may be affected alone or in combination. Hematological manifestations of MID include aplastic, megaloblastic, or sideroblastic anemia, leukopenia, neutropenia, thrombocytopenia, or pancytopenia. In single cases either permanent or recurrent eosinophilia has been observed. Hematological abnormalities may occur together with syndromic or nonsyndromic MIDs. Syndromic MIDs, in which hematological manifestations predominate, are the Pearson syndrome (pancytopenia), Kearns-Sayre syndrome (anemia), Barth syndrome (neutropenia), and the autosomal recessive mitochondrial myopathy, lactic acidosis and sideroblastic anemia syndrome. In single cases with Leigh's syndrome, MERRF (myoclonic epilepsy and ragged-red fiber) syndrome, Leber's hereditary optic neuropathy, and Friedreich's ataxia anemia has been described. Anemia, leukopenia, thrombocytopenia, eosinophilia, or pancytopenia can frequently also be found in nonsyndromic MIDs with or without involvement of other tissues. Therapy of blood cell involvement in MID comprises application of antioxidants, vitamins, iron, bone marrow-stimulating factors, or substitution of cells.

Mitochondrial DNA deletions sensitize cells to apoptosis at low heteroplasmy levels

A heterogeneous group of multisystem disorders affecting various tissues and often including neuromuscular symptoms is caused by mutations of the mitochondrial genome, which codes 13 polypeptides of oxidative phosphorylation (OXPHOS) complexes and 22 tRNA genes needed for their translation. Since the link between OXPHOS dysfunction and clinical phenotype remains enigmatic in many diseases, a possible role of enhanced apoptosis is discussed besides bioenergetic crisis of affected cells. We analyzed the proapoptotic impact of the mitochondrial 5kb common deletion (CD), affecting five tRNA genes, in transmitochondrial cybrid cell lines and found a slightly enhanced sensitivity to exogenous oxidative stress (H2O2) and a pronounced sensitization against death receptor stimulation (TRAIL) at a rather low CD heteroplasmy level of 22%. Mitochondrial deletions confer enhanced susceptibility against proapoptotic signals to proliferating cells, which might explain the elimination of deletions from hematopoietic stem cells.

mtDNA single macrodeletions associated with myopathies: absence of haplogroup-related increased risk

As for any non-recombining genome, any mutation at mtDNA, if not recurrent, appears on a particular haplotype background, allowing its detection by haplogroup association studies. It has been shown that the propensity for occurrence of single macrodeletions at a level beyond the pathological threshold is associated with super-haplogroup U/K. However, in this report, we present evidence for the absence of preferential haplogroup backgrounds for single macrodeletions. We have analysed how haplogroup diagnostic polymorphisms could disrupt direct repeats usually flanking the deleted segment, and we have concluded that for the Common Deletion, no such polymorphisms are observed in humans, but they do occur in other primates. Furthermore, we also report five new single macrodeletions.

Progression in a case of Kearns-Sayre syndrome

The quantitative relationship between deleted mitochondrial DNA and the clinical course of patients with Kearns-Sayre syndrome is poorly understood. We investigated this point using tissue samples obtained at age 10 years when the patient was diagnosed as Kearns-Sayre syndrome and at age 20 years when he died of disseminated intravascular coagulation. By long polymerase chain reaction, a shortened mitochondrial genome (8.8 kb; normal, 16.6 kb) was detected in the patient. By quantitative competitive polymerase chain reaction, the percentage of deletion-carrying mitochondrial DNA was not increased as expected and did not differ significantly by tissue type or sampling time or correlate with clinical course. Although we could not demonstrate that the amounts of wild-type mitochondrial DNA decreased with accelerating progression, it was emphasized that such a reduction of mitochondrial DNA in various tissues, including those of the central nervous system, could play a significant pathogenetic role, since only wild-type mitochondrial DNA is functional in patients with large-scale deletions of mitochondrial DNA.