Deep sequencing unearths nuclear mitochondrial sequences under Leber's hereditary optic neuropathy-associated false heteroplasmic mitochondrial DNA variants.

Leber's hereditary optic neuropathy (LHON) is associated with mitochondrial DNA (mtDNA) ND mutations that are mostly homoplasmic. However, these mutations are not sufficient to explain the peculiar features of penetrance and the tissue-specific expression of the disease and are believed to be causative in association with unknown environmental or other genetic factors. Discerning between clear-cut pathogenetic variants, such as those that appear to be heteroplasmic, and less penetrant variants, such as the homoplasmic, remains a challenging issue that we have addressed here using next-generation sequencing approach. We set up a protocol to quantify MTND5 heteroplasmy levels in a family in which the proband manifests a LHON phenotype. Furthermore, to study this mtDNA haplotype, we applied the cybridization protocol. The results demonstrate that the mutations are mostly homoplasmic, whereas the suspected heteroplasmic feature of the observed mutations is due to the co-amplification of Nuclear mitochondrial Sequences.

Bilateral progressive visual loss in an epileptic, mentally retarded boy.

Leber's hereditary optic neuropathy (LHON) is a maternally inherited, monosymptomatic disorder, characterized by severe central vision loss and optic atrophy that most frequently affects young men. The classic LHON phenotype is associated to three mitochondrial DNA mutations, mostly homoplasmic, in the Mt-ND4, Mt-ND6, and Mt-ND1 genes, encoding for complex I subunits of the mitochondrial respiratory chain. Rare cases have been described in the literature in association with variable central nervous system involvement in a syndromic form called LHON 'plus.' In the present study, we report the case of a 16-year-old boy with the 3460/ND1 mutation who presented with epilepsy, migraine, and mental retardation as non-ophthalmic features. We also investigated his relatives who all had the 3460/ND1 mutation.

Late-onset Leber hereditary optic neuropathy mimicking Susac's syndrome.

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder characterized by bilateral painless optic atrophy and blindness. It usually occurs in young men in association with three major mutations in the mitochondrial genome (mtDNA). We report a patient with a history of alcohol abuse who developed at age 63 years visual impairment, sensorineural hearing loss, and memory dysfunction, suggestive of Susac's syndrome. The patient carried the heteroplasmic mt. 11778G>A mutation on the T2e mtDNA haplogroup. It remains unclear if chronic alcohol abuse combined with the mitochondrial genetic background prompted an aged-related neurodegeneration or deferred the onset of the LHON disease.

A new locus on 3p23-p25 for an autosomal-dominant limb-girdle muscular dystrophy, LGMD1H.

Limb-girdle muscular dystrophies (LGMDs) are a genetically heterogeneous group of neuromuscular disorders with a selective or predominant involvement of shoulder and pelvic girdles. We clinically examined 19 members in a four-generation Italian family with autosomal-dominant LGMD. A total of 11 subjects were affected. Clinical findings showed variable expressivity in terms of age at onset and disease severity. Five subjects presented with a slowly progressive proximal muscle weakness, in both upper and lower limbs, with onset during the fourth-fifth decade of life, which fulfilled the consensus diagnostic criteria for LGMD. Earlier onset of the disease was observed in a group of patients presenting with muscle weakness and/or calf hypertrophy, and/or occasionally high CK and lactate serum levels. Two muscle biopsies showed morphological findings compatible with MD associated with subsarcolemmal accumulation of mitochondria and the presence of multiple mitochondrial DNA deletions. A genome-wide scan performed using microsatellite markers mapped the disease on chromosome 3p23-p25.1 locus in a 25-cM region between markers D3S1263 and D3S3685. The highest two-point LOD score was 3.26 (theta=0) at marker D3S1286 and D3S3613, whereas non-parametric analysis reached a P-value=0.0004. Four candidate genes within the refined region were analysed but did not reveal any mutations. Our findings further expand the clinical and genetic heterogeneity of LGMDs.

Molecular analysis in a family presenting with a mild form of late-onset autosomal dominant chronic progressive external ophthalmoplegia.

Nuclear genes affecting mitochondrial genome stability were screened in an Italian family presenting with autosomal dominant progressive external ophthalmoplegia (adPEO) associated with multiple mitochondrial DNA (mtDNA) deletions. We report on a heterozygous c.907C>T (p.R303W) mutation found in the N-terminal domain of the human mitochondrial DNA helicase, Twinkle protein, in six members of a family, in which two individuals manifested late-onset PEO and morphological and molecular signs of mitochondrial dysfunction along with two carriers who are presently free of disease manifestation. We also investigated if the p.R303W mutation in PEO1 gene affected the relative copy number of mitochondrial DNA genomes.

Bilateral striatal necrosis, dystonia and multiple mitochondrial DNA deletions: case study and effect of deep brain stimulation.

Bilateral striatal necrosis (BSN) is relatively rare and has been related to a wide array of causes, including nuclear and mitochondrial DNA mutations. We report the clinical vignette of a patient with a 37 year-history of generalized dystonia secondary to BSN associated with multiple mitochondrial DNA deletions of undefined origin. Globus pallidus interna deep brain stimulation produced sustained benefit, with predominant improvements in disability.