Familial mitochondrial myopathy with cataract

Regulation of mitochondrial respiratory chain biogenesis by estrogens/estrogen receptors and physiological, pathological and pharmacological implications

There has been increasing evidence pointing to the mitochondrial respiratory chain (MRC) as a novel and important target for the actions of 17beta-estradiol (E(2)) and estrogen receptors (ER) in a number of cell types and tissues that have high demands for mitochondrial energy metabolism. This novel E(2)-mediated mitochondrial pathway involves the cooperation of both nuclear and mitochondrial ERalpha and ERbeta and their co-activators on the coordinate regulation of both nuclear DNA- and mitochondrial DNA-encoded genes for MRC proteins. In this paper, we have: 1) comprehensively reviewed studies that reveal a novel role of estrogens and ERs in the regulation of MRC biogenesis; 2) discussed their physiological, pathological and pharmacological implications in the control of cell proliferation and apoptosis in relation to estrogen-mediated carcinogenesis, anti-cancer drug resistance in human breast cancer cells, neuroprotection for Alzheimer's disease and Parkinson's disease in brain, cardiovascular protection in human heart and their beneficial effects in lens physiology related to cataract in the eye; and 3) pointed out new research directions to address the key questions in this important and newly emerging area. We also suggest a novel conceptual approach that will contribute to innovative regimens for the prevention or treatment of a wide variety of medical complications based on E(2)/ER-mediated MRC biogenesis pathway.

The role of mitochondrial DNA mutations in mammalian aging

Mitochondrial DNA (mtDNA) accumulates both base-substitution mutations and deletions with aging in several tissues in mammals. Here, we examine the evidence supporting a causative role for mtDNA mutations in mammalian aging. We describe and compare human diseases and mouse models associated with mitochondrial genome instability. We also discuss potential mechanisms for the generation of these mutations and the means by which they may mediate their pathological consequences. Strategies for slowing the accumulation and attenuating the effects of mtDNA mutations are discussed.

A gene for X-linked idiopathic congenital nystagmus (NYS1) maps to chromosome Xp11.4-p11.3

Congenital nystagmus (CN) is a common oculomotor disorder (frequency of 1/1,500 live births) characterized by bilateral uncontrollable ocular oscillations, with onset typically at birth or within the first few months of life. This condition is regarded as idiopathic, after exclusion of nervous and ocular diseases. X-linked, autosomal dominant, and autosomal recessive modes of inheritance have been reported, but X-linked inheritance is probably the most common. In this article, we report the mapping of a gene for X-linked dominant CN (NYS1) to the short arm of chromosome X, by showing close linkage of NYS1 to polymorphic markers on chromosome Xp11.4-p11.3 (maximum LOD score of 3.20, over locus DXS993). Because no candidate gene, by virtue of its function, has been found in this region of chromosome Xp, further studies are required, to reduce the genetic interval encompassing the NYS1 gene. It is hoped that the complete gene characterization will address the complex pathophysiology of CN.

Transient postictal cortical blindness

An 8-year-old boy with insulin-dependent diabetes mellitus and a seizure disorder demonstrated transient visual loss after severe seizure activity. The role of hypoglycemia in relation to his transient cortical blindness remains indeterminate. The nature of the cortical involvement, the rate of visual recovery, and prior reports of postictal phenomena emphasize the relatively benign nature of this condition in children.

Mitochondrial inheritance in a mitochondrially mediated disease

Mendelian inheritance involves the transmission to successive generations of DNA contained in genes in the nucleus, but DNA is also contained in mitochondria, where it is believed to be responsible for the encoding of certain mitochondrial enzymes. Since nearly all mitochondrial DNA is maternally transmitted, one might expect a nonmendelian pattern of inheritance in mitochondrial cytopathy, a syndrome in which there are abnormalities in mitochondrial structure and deficiencies in a variety of mitochondrial enzymes. We studied the pedigrees of 6 affected families whose members we had examined personally and of 24 families described in the literature. In 27 families, exclusively maternal transmission occurred; in 3 there was also paternal transmission in one generation. Altogether, 51 mothers but only 3 fathers had transmitted the condition. These results are consistent with mitochondrial transmission of mitochondrial cytopathy; the inheritance and enzyme defects of mitochondrial cytopathy can be considered in the light of recent evidence that subunits of respiratory-enzyme complexes are encoded solely by mitochondrial DNA. The occasional paternal transmission may be explained if certain enzyme subunits that are encoded by nuclear DNA are affected.

Kearns syndrome: a heterogeneous group of disorders with CPEO, or a nosological entity?

In connection with 4 new cases of Kearns syndrome (multisystem form of mitochondrial CPEO), the condition was found to be present in slight to oligosymptomatic form in all 4 families. The marker symptom in subclinical patients was nearly always ptosis (sometimes very slight) and occasionally diabetes. In the literature other endocrine disorders, retinal anomalies, deafness, growth disturbances, etc., have been noted as subclinical symptoms in former generations. Heredity appears to be autosomal dominant in these 4 families, with very variable expressivity. The possibility that one gene is responsible for the disease seems to be plausible, but the marked variation in expressivity suggests a modifying influence of other alleles; in this sense, therefore, one may speak of multifactor inheritance. Supporting facts could also be found in the literature, where there was autosomal dominant heredity of the disease-carrying gene, but for its complete expression 'amplifying' factors (alleles) were needed. The pleiotropia of the disease-carrying gene is explained by a mitochondrial disorder of various organs. On the basis of the heredity, therefore, Kearns syndrome is not a syndrome but a disease. The most serious, most progressive and most extensive (multisystem) variant of Kearns disease is the infantile form, known as the 'Kearns-Sayre syndrome. When the expressivity of the disease is less extensive it usually occurs later in life and is less progressive: the adult form of Kearns disease.