The specific mitochondrial DNA polymorphism found in Klinefelter's syndrome

Next Generation Sequencing expression profiling of mitochondrial subunits in men with Klinefelter syndrome

Objectives: Klinefelter syndrome (KS) is one of the most common sex-chromosome disorders as it affects up to 1 in every 600-1000 newborn males. Men with KS carry one extra X chromosome and they usually present a 47,XXY karyotype, but less frequent variants have also been reported in literature. KS typical symptoms include tall stature, gynecomastia, broad hips, hypogonadism and absent spermatogenesis. The syndrome is also related to a wide range of cognitive deficits, among which language-based learning disabilities and verbal cognition impairment are frequently diagnosed. The present study was carried out to investigate the role of mitochondrial subunits in KS, since the molecular mechanisms underlying KS pathogenesis are not fully understood. Methods: The study was performed by the next generation sequencing analysis and qRT-PCR assay. Results: We were able to identify a significant down-expression of mitochondrial encoded NADH: ubiquinone oxidoreductase core subunit 6 (MT-ND6) in men with KS. Conclusion: It is known that defects of the mtDNA encoding mitochondrial subunits are responsible for the malfunction of Complex I, which will eventually lead to the Complex I deficiency, the most common respiratory chain defect in human disorders. Since it has been shown that decreased Complex I protein levels could induce apoptosis, wehypothesizethat the above-mentioned MT-ND6 down-expression contributes to the wide range of phenotypes observed in men with KS.

A case of Madelung's disease accompanied by Klinefelter's syndrome

Madelung's disease is a rare fat metabolism disorder characterised by benign multiple symmetric, encapsulated lipomatosis. The exact cause of the disease is unknown; it may be associated with chronic alcoholism and mutations in mitochondrial DNA (A8344G), but there have been cases without these factors reported in the literature. A 29-year-old man with a 6-year history of diabetes mellitus was admitted to our hospital for poorly regulated diabetes and decreased libido. He was not an alcohol consumer. His family history was unremarkable. Physical examination revealed that he had a eunuchoid body shape. There was a symmetric excess fat accumulation in his submandibular, deltoid, nuchal, suprapubic and inguinal areas. He was diagnosed with Madelung's disease, and imaging studies supported the diagnosis. Hormonal evaluation revealed a hypergonadotropic hypogonadism. Karyotype analysis revealed a 47,XXY mutation. Genetic research showed no mitochondrial DNA mutation. Metabolic disorders, such as diabetes mellitus, hyperlipidaemia, hyperuricaemia and liver disease, endocrine gland diseases, such as hypothyroidism, and neurological diseases, such as polyneuropathy and cognitive disorders, may accompany Madelung's disease. The present study represents the first reported case of Madelung's disease accompanied by Klinefelter's syndrome.

LEARNING POINTS

Madelung's disease is a rare fat metabolism disorder characterised by benign multiple symmetric and encapsulated lipid accumulation.The exact cause of the disease is unknown.Metabolic disorders, such as diabetes mellitus, hyperlipidaemia, hyperuricaemia and liver disease, endocrine gland diseases, such as hypothyroidism, and neurological diseases, such as polyneuropathy and cognitive disorders, may accompany Madelung's disease.

Mutation C11994T in the mitochondrial ND4 gene is not a cause of low sperm motility in Portugal

It has recently been suggested that a hitherto unobserved mutation, C11994T, causes oligoasthenozoospermia in men from India but at the same time does not affect systems other than the motility of the sperm. There are good reasons to question this proposition, in view of the worldwide mtDNA database and the Indian record in particular. We have further analyzed the oligoasthenozoospermic samples from a previous systematic study of infertile Portuguese men and found no instance of C11994T.

Difficulties and possible solutions in the genetic management of mtDNA disease in the preimplantation embryo

Families who have had a child die of a severe, maternally inherited mitochondrial DNA (mtDNA) disease are usually desperate to avoid having further affected children. Here we discuss the problems of applying classical genetic management to mtDNA diseases (Poulton and Turnbull, 2000) and the biology underlying these problems. We explain why these disorders have lagged so far behind the genetics revolution. We then outline the directions in which management is likely to develop, including the use of preimplantation genetic diagnosis (PGD).

Association studies on human mitochondrial DNA: methodological aspects and results in the most common age-related diseases

Mitochondrial DNA (mtDNA) follows direct maternal inheritance and, as such, can be used in phylogenetic studies to determine a human lineage tree. The presence of common polymorphisms allows a classification of mtDNA in haplogroups and sub-haplogroups, according to the branch they belong to. Thanks to the rapidly growing number of mtDNA sequences available, this classification is being corrected and redefined to be more accurate. In parallel with this process, several studies are trying to identify an association between common mtDNA polymorphisms and common complex traits, as hypothesized by the common disease-common variant theory. Here we review the associations already reported with the main age-related complex diseases and we identify the critical points (sample size, size of the recruiting area, careful matching between cases and controls regarding geographical origin and ethnicity, data quality checking) to be taken in account in planning such studies. On the whole, this research area is opening a new perspective as an important component of "mitochondrial medicine", capable of identifying new molecular targets for the diagnosis, prevention and treatment of common complex diseases.

Phantom mutation hotspots in human mitochondrial DNA

Phantom mutations are systematic artifacts generated in the course of the sequencing process. Contra common belief these artificial mutations are nearly ubiquitous in sequencing results, albeit at frequencies that may vary dramatically. The amount of artifacts depends not only on the sort of automated sequencer and sequencing chemistry employed, but also on other lab-specific factors. An experimental study executed on four samples under various combinations of sequencing conditions revealed a number of phantom mutations occurring at the same sites of mitochondrial DNA (mtDNA) repeatedly. To confirm these and identify further hotspots for artifacts, > 5000 mtDNA electropherograms were screened for artificial patterns. Further, > 30 000 published hypervariable segment I sequences were compared at potential hotspots for phantom mutations, especially for variation at positions 16085 and 16197. Resequencing of several samples confirmed the artificial nature of these and other polymorphisms in the original publications. Single-strand sequencing, as typically executed in medical and anthropological studies, is thus highly vulnerable to this kind of artifacts. In particular, phantom mutation hotspots could easily lead to misidentification of somatic mutations and to misinterpretations in all kinds of clinical mtDNA studies.

Neurodegenerative disorders associated with diabetes mellitus

More than 20 syndromes among the significant and increasing number of degenerative diseases of neuronal tissues are known to be associated with diabetes mellitus, increased insulin resistance and obesity, disturbed insulin sensitivity, and excessive or impaired insulin secretion. This review briefly presents such syndromes, including Alzheimer disease, ataxia-telangiectasia, Down syndrome/trisomy 21, Friedreich ataxia, Huntington disease, several disorders of mitochondria, myotonic dystrophy, Parkinson disease, Prader-Willi syndrome, Werner syndrome, Wolfram syndrome, mitochondrial disorders affecting oxidative phosphorylation, and vitamin B(1) deficiency/inherited thiamine-responsive megaloblastic anemia syndrome as well as their respective relationship to malignancies, cancer, and aging and the nature of their inheritance (including triplet repeat expansions), genetic loci, and corresponding functional biochemistry. Discussed in further detail are disturbances of glucose metabolism including impaired glucose tolerance and both insulin-dependent and non-insulin-dependent diabetes caused by neurodegeneration in humans and mice, sometimes accompanied by degeneration of pancreatic beta-cells. Concordant mouse models obtained by targeted disruption (knock-out), knock-in, or transgenic overexpression of the respective transgene are also described. Preliminary conclusions suggest that many of the diabetogenic neurodegenerative disorders are related to alterations in oxidative phosphorylation (OXPHOS) and mitochondrial nutrient metabolism, which coincide with aberrant protein precipitation in the majority of affected individuals.