A 13084 A->T missense mutation in the mitochondrial ND5 gene was identified in a 16-year-old boy affected with a progressive neurodegenerative disorder combining features of Leigh and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes) syndromes. Muscle biopsy analysis revealed partial complex I deficiency. The mutation presented a variable degree of heteroplasmy in the patient’s tissues. This finding underlines the contribution of mtDNA-encoded complex I subunits in the etiology of complex I deficiency associated with encephalopathy.

We have identified a heteroplasmic G to A mutation at position 12,183 of the mitochondrial transfer RNA Histidine (tRNA(His)) gene in three related patients. These phenotypes varied according to mutation heteroplasmy: one had severe pigmentary retinopathy, neurosensorial deafness, testicular dysfunction, muscle hypotrophy, and ataxia; the other two had only retinal and inner ear involvement. The mutation is in a highly conserved region of the T(psi)C stem of the tRNA(His) gene and may alter secondary structure formation. This is the first described pathogenic, maternally inherited mutation of the mitochondrial tRNA(His) gene.

Annals of NeurologyVolume 49, Issue 1 p. 137-138 Letter Down's syndrome fibroblasts anticipate the accumulation of specific ageing-related mtDNA mutations Roberto Del Bo PhD, Roberto Del Bo PhD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorGiacomo Pietro Comi MD, Giacomo Pietro Comi MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorMaria Paola Perini MD, Maria Paola Perini MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorSandra Strazzer MD, Sandra Strazzer MD I.R.C.S.S. “E. Medea” de La Nostra Famiglia, Bosisio Parini, ItalySearch for more papers by this authorNereo Bresolin MD, Nereo Bresolin MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, Italy I.R.C.S.S. “E. Medea” de La Nostra Famiglia, Bosisio Parini, ItalySearch for more papers by this authorGuglielmo Scarlato MD, Guglielmo Scarlato MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this author Roberto Del Bo PhD, Roberto Del Bo PhD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorGiacomo Pietro Comi MD, Giacomo Pietro Comi MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorMaria Paola Perini MD, Maria Paola Perini MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this authorSandra Strazzer MD, Sandra Strazzer MD I.R.C.S.S. “E. Medea” de La Nostra Famiglia, Bosisio Parini, ItalySearch for more papers by this authorNereo Bresolin MD, Nereo Bresolin MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, Italy I.R.C.S.S. “E. Medea” de La Nostra Famiglia, Bosisio Parini, ItalySearch for more papers by this authorGuglielmo Scarlato MD, Guglielmo Scarlato MD Centro Dino Ferrari, Istituto di Clinica Neurologica, Università degli Studi di Milano, I.R.C.S.S. Ospedale Maggiore Policlinico, Milano, ItalySearch for more papers by this author First published: 16 January 2001 https://doi.org/10.1002/1531-8249(200101)49:1<137::AID-ANA26>3.0.CO;2-ICitations: 4Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume49, Issue1January 2001Pages 137-138 RelatedInformation

Three cases of Leigh disease are described. In all three, symptoms began in the first months of life, with muscle hypotonia, lactic acidosis, and psychomotor delay. The diagnosis was made on the basis of the clinical characteristics, biochemical abnormalities, and typical brain magnetic resonance imaging with symmetric lesions suggesting bilateral necrosis at the level of the basal ganglia and of the midbrain. Cytochrome c oxidase (complex IV of the mitochondrial respiratory chain) deficiency was demonstrated in muscle tissue in all patients and confirmed in skin fibroblasts in patient 3. A genetic heterogeneity was present in these patients since only one had a SURF-1 gene mutation. The clinical, biochemical, and neuroradiologic aspects are discussed. Finally, the finding of facial dysmorphisms in the cytochrome c oxidase deficiency observed in one of the described cases is of extreme interest; to our knowledge, this association has never been reported in the literature. (J Child Neurol 2001;16:608-613).

DNA methylation is one of the mechanism for regulating gene expression. Transfected cells in tissue culture are a mosaic of expression of the exogenous gene. 5' azacytidine (Aza C), inhibiting nuclear DNA methyltransferase, causes an increase of expression of E.coli alpha-galactosidase (LacZ) in transfected CHO cells.Murine muscle cell lines G8 and C2C12 were transfected by biolistic technique with plasmids carrying a reporter gene pCMVlacZ and pY3 that confers resistance to Hygromycin B. Resistant clones have been treated with different concentrations of 5' azacytidine and analyzed by X-gal stain and Southern Blotting of DNA, after various time intervals up to one month. Hygromycin resistant cells were: transplanted in the tibialis anterior muscle of living mice. Aza C was injected subcutaneously above the treated muscle. Histochemistry with X-gal was performed after different treatment periods, in order to evaluate the reporter gene expression timings.The myogenic cell lines, after treatment with 5' azacytidine in vitro, express the exogenous gene at different levels, with four fold enhancement in G8 cells, after 15 days from transfection. The enhancement of expression is directly derived from the inhibition of methylation as shown by DNA restriction analysis. Mouse muscular samples treated subcutaneously with 5' azacytidine showed an enhancement of lacZ expression in vivo up to 20 days after transfection.5' azacytidine enhances the level and the time span of exogenous gene expression in muscle cells facilitating gene therapy studies.

Loss-of-function mutations of the SURF-1 gene have been associated with Leigh syndrome with cytochrome c oxidase (COX) deficiency. Mature Surf-1 protein (Surf-1p) is a 30 kDa hydrophobic polypeptide whose function is still unknown. Using antibodies against a recombinant, hemagglutinin-tagged Surf-1p, we have demonstrated that this protein is imported into mitochondria as a larger precursor, which is then processed into the mature product by cleaving off an N-terminal leader polypeptide of approximately 40 amino acids. By using western blot analysis with specific antibodies, we showed that Surf-1p is localized in and tightly bound to the mitochondrial inner membrane. The same analysis revealed that no protein is present in cell lines harboring loss-of-function mutations of SURF-1, regardless of their type and position. Northern blot analysis showed the virtual absence of specific SURF-1 transcripts in different mutant cell lines. This result suggests that several mutations of SURF-1 are associated with severe mRNA instability. To understand better whether and which domains of the protein are essential for function, we generated several constructs with truncated or partially deleted SURF-1 cDNAs. None of these constructs, expressed into Surf-1p null mutant cells, were able to rescue the COX phenotype, suggesting that different regions of the protein are all essential for function. Finally, experiments based on blue native two-dimensional gel electrophoresis indicated that assembly of COX in Surf-1p null mutants is blocked at an early step, most likely before the incorporation of subunit II in the nascent intermediates composed of subunit I alone or subunit I plus subunit IV. However, detection of residual amounts of fully assembled complex suggests a certain degree of redundancy of this system.

Usher syndrome (US) is an autosomal recessive disorder characterized by congenital bilateral sensorineural hearing loss and progressive loss of vision secondary to retinitis pigmentosa. US can be divided into several clinical types. Types 1 and 2 are the most common subtypes. Type 3, which is associated with progressive hearing loss, is more uncommon. The hallmark of US type 1 is congenital impairment of the vestibular system. Type 1 is characterized by severe to profound sensorineural hearing loss, absent vestibular function, and RP. Type 2 is characterized by moderate to severe sensorineural hearing loss, normal vestibular function and RP. Although clinically there are two main types of US, research has proven that genetic heterogeneity exists within each type. Three genes for US type 1 and two genes for US type 2 have been identified. Genetic heterogeneity also limits the use of DNA markers in the early diagnosis of US. At the present time, children with US are typically not diagnosed until adolescence or young adulthood. Delay in diagnosis often occurs because of the insidious nature of the visual abnormalities. This paper describes of clinical criteria recommended for the diagnosis of US and the main disorders with deafness and low vision associated.

Leber's hereditary optic neuropathy (LHON), is a maternally inherited disease causing severe and progressive visual loss, predominantly in young men. Genealogical data have suggested a mitochondrial inheritance supported by the discovery of three mitochondrial point mutations (11778, 3460, 14484), associated with Leber's disease. Fifteen other secondary mtDNA mutations have been identified but their linkage with LHON is still uncertain. Supported by recent advances in mitochondrial genetics the clinical characteristics of LHON are critically reviewed. "Leber's plus" is a term to describe patients with clinical features of LHON in addition to other severe neurological or systemic abnormalities like multiple sclerosis-like syndrome, dystonia, ataxia, peripheral neuropathy, Wolf-Parkinson-White syndrome, Wolfram syndrome, etc. The mitochondrial pathogenetic mechanisms are also discussed: different mutations result in uneven degrees of optic neuropathy. The described intra/interfamiliar variability in CNS involvement cannot be often explained by tissue heteroplasmy; finally the role of multiple genomic interactions still remains to be considered.