Mitochondrial DNA deletions in progressive external ophthalmoplegia and Kearns-Sayre syndrome

Article Abstract:

Kearns-Sayre syndrome is an inherited disorder characterized by eye muscle paralysis, pigment degeneration of the retina (responds to visual stimuli and connects with the optic nerve), and dysfunction of the heart and brain. The defect causing this disease can be traced to the mitochondria of the cell. The human cell has a nucleus which contains DNA, the genetic material inherited from both parents. In addition, the mitochondria, the energy producing organ of the cell, has its own separate DNA which is responsible for the production of certain proteins used for cellular activities. This mitochondrial DNA is contributed solely by the mother during the fertilization process. Diseases produced as a result of mutated mitochondrial DNA can be passed to both male and female children, but only daughters will pass on the disease. In 123 patients with various mitochondrial muscle or brain diseases, 32 patients having muscle paralysis and ophthalmoplegia also had portions of the mitochondrial chromosomes deleted. The mitochondrial DNA deletions affected mitochondrial function and resulted in the disease. It is suggested that the exact location of the deletion dictates the particular protein affected.

Abnormalities, DNA, Eye, Mitochondrial DNA, Ophthalmoplegia

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Mosaic expression of dystrophin in symptomatic carriers of Duchenne's muscular dystrophy

Article Abstract:

Duchenne's muscular dystrophy is characterized by muscle weakness and wasting; it is a genetic defect that is inherited through the mother and passed on to sons. The defect decreases the production of the protein dystrophin in muscle tissue. Almost 70 percent of the mothers of patients with Duchenne's muscular dystrophy are thought to be carriers of the disease and 70 percent of that number have some muscle weakness of their own. The skeletal muscle cells of three carriers with the responsible gene were examined for dystrophin. It was found that the cells from symptomatic carriers had a definite mosaic pattern, and 80 percent of the carriers were lacking dystrophin. It is suggested that the mosaic pattern found in muscle cells can be used to identify symptomatic carriers, which would be useful in genetic counseling. It is unknown whether this cell pattern will be found in mothers having no symptoms of muscle involvement.

Methods, Genetic screening, Genetic testing, Cytoskeletal proteins, Duchenne muscular dystrophy

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Molecular genetic heterogeneity of myophosphorylase deficiency (McArdle's disease)

Article Abstract:

One type of mutation in the gene for myophosphorylase may occur more often than any other among patients with McArdle's disease. McArdle's disease is a genetic disorder that is caused by a deficiency of myophosphorylase, an enzyme found in muscle tissue. A study examined genetic mutations in the gene for myophosphorylase using restriction-endonuclease analysis in 40 patients between 13 weeks and 62 years old with McArdle's disease. Three different types of mutations were found. The most common type involved substitution of the nucleic acid thymine for the nucleic acid cysteine at codon 49. The frequency of this mutation implies that 90% of of the patients with McArdle's disease may be diagnosed by genetic analysis of their white blood cells. This would eliminate the need for a muscle biopsy.

Evaluation, Diagnosis, Enzymes, Genetic disorders, Chromosome abnormalities

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