A patient who wished to be treated for infertility by intracytoplasmic sperm injection (ICSI) was referred to our group for assessment. Upon clinical examination, a ptosis (partial closure of the eyelid) was noted, and histology revealed ragged red fibres in the skeletal muscle. Southern blot analysis of spermatozoa and skeletal muscle revealed the presence of multiple mitochondrial DNA deletions. This kind of rearrangement may be of nuclear origin since three nuclear loci have been ascribed to multiple mitochondrial DNA deletions in humans. Since mitochondrial DNA is maternally transmitted, the use of ICSI was feasible. However, an alteration of nuclear gene product affecting the integrity of mitochondrial DNA, and thus sperm mobility, might be transmitted to the offspring with the risk of developing a mitochondrial DNA disease.

Oligoasthenospermia associated with multiple mitochondrial DNA rearrangements.

Leber hereditary optic neuropathy (LHON) is a maternally inherited disease characterized by acute or subacute painless central visual loss usually in young adults, predominantly in males. Except for optic atrophy, LHON patients are usually otherwise healthy. Occasionally, LHON is associated with neurological, cardiac, and skeletal changes. The clinical course of LHON has several stages. Peripapillary microangiopathy is present from the beginning. Microangiopathy disappears as the disease progresses towards the end stages. Simultaneously, the retinal nerve fiber layer fades from view, first papillomacular nerve fiber bundles, and months later, the whole nerve fiber layer becomes atrophic. At the end stage the centrocecal scotoma is large and absolute. Loss of vision is usually permanent, but spontaneous recovery can occur. Despite a few attempts, no effective treatment to prevent or halt LHON has been found. Several mitochondrial DNA (mtDNA) mutations are associated with LHON, but the pathogenic processes leading to optic nerve atrophy are largely unknown. About 15% of the families are heteroplasmic, i.e., both mutant and wild type mtDNA coexist within an individual. The level of heteroplasmy between different tissues can vary markedly. mtDNA mutations are not sufficient to cause visual loss in LHON, since not all individuals harboring a pathogenic LHON mutation express the disease. There are additional genetic and/or environmental precipitating factors, but thus far they are unknown.

Leber hereditary optic neuropathy: clinical and molecular genetic findings

Leber's hereditary optic neuropathy (LHON) accounts for about 3% of the cases of blindness in young adult males. The underlying mitochondrial pathogenesis of LHON has been well studied, with specific mitochondrial DNA (mtDNA) mutations of structural genes described and well characterized. However, enigmatic aspects of the disease are not explained by mutation data, such as the higher proportion of affected males, the later onset of the disease in females, and the presence of unaffected individuals with a high proportion of mutant mtDNA. A hypothesis which has been put forward to explain the unusual disease expression is a dual model of mtDNA and X-linked nuclear gene inheritance. If a nuclear X-linked modifier gene influences the expression of the mitochondrial-linked mutant gene then the affected females should be either homozygous for the nuclear determinant, or if heterozygous, lyonization should favor the mutant X. In order to determine if an X-linked gene predisposes to LHON phenotype we studied X-inactivation patterns in 35 females with known mtDNA mutations from 10 LHON pedigrees. Our results do not support a strong X-linked determinant in LHON cause: 2 of the 10 (20%) manifesting carriers showed skewing of X-inactivation, as did 3 of the 25 (12%) nonmanifesting carriers.

X-inactivation patterns in female Leber's hereditary optic neuropathy patients do not support a strong X-linked determinant.

Leber hereditary optic neuropathy (LHON) is maternally transmitted and is characterized by bilateral loss of central vision in young adults as a result of optic nerve degeneration. Fifteen transition mutations located in different genes for the mitochondrially encoded subunits of respiratory chain complexes have been associated thus far with the disease. Genetic studies have led to the classification of the pathogenic significance of these different mutations. However, more research is required to determine the causality of the mutations and the penetrance of the disease. The present study compares studies of populations of different ethnic origins, namely European LHON pedigrees and sporadic cases, in order to elucidate the pathogenic mechanisms involved. 21 refs., 2 figs., 1 tab.

Features of mtDNA mutation patterns in European pedigrees and sporadic cases with Leber hereditary optic neuropathy.

The occurrence of a multiple sclerosis (MS)-like phenotype in subjects carrying mitochondrial DNA (mtDNA) mutations associated with Leber hereditary optic neuropathy (LHON) has suggested that mitochondrial genes may contribute to susceptibility to MS. With the present study 74 unrelated Italian patients (53 females and 21 males; mean age 37.9, SD 9.9, range 20-59) affected by MS with early and prominent optic nerve involvement and 99 normal control subjects were analysed for the presence of primary (nps 11778, 3460, 14484) and an alleged secondary one (np 15257) LHON mutations. A single MS patient carrying a virtually homoplasmic LHON mutation at np 11778 was found. Family history revealed a maternal uncle affected by MS, decreased at age of 64 in consequence of a stroke. The patient's mother harboured the same mutation in a homoplasmic way. Primary LHON mutations were not detected in any other MS patient or control. Of the MS patients 5.4% (4 out of 74), and 5.1% (5 out of 99) of the controls carried the 15257 mutation in a homoplasmic state. Present data do not support any contribution of primary LHON mutations to genetically determined susceptibility in MS. There is no evidence that the 15257 mutation has any pathogenetic significance in the Italian population.

LHON mutations in Italian patients affected by multiple sclerosis.

No genetic differences between affected and unaffected members of a German family with Leber's hereditary optic neuropathy (LHON) with respect to ten mtDNA point mutations associated with LHON.

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No genetic differences between affected and unaffected members of a German family with Leber's hereditary optic neuropathy (LHON) with respect to ten mtDNA point mutations associated with LHON.