New evidence of a mitochondrial genetic background paradox: Impact of the J haplogroup on the A3243G mutation

International audienceBackground: The A3243G mutation in the tRNALeu gene (UUR), is one of the most common pathogenic mitochondrial DNA (mtDNA) mutations in France, and is associated with highly variable and heterogeneous disease phenotypes. To define the relationships between the A3243G mutation and mtDNA backgrounds, we determined the haplogroup affiliation of 142 unrelated French patients – diagnosed as carriers of the A3243G mutation – by control-region sequencing and RFLP survey of their mtDNAs. Results: The analysis revealed 111 different haplotypes encompassing all European haplogroups, indicating that the 3243 site might be a mutational hot spot. However, contrary to previous findings, we observed a statistically significant underepresentation of the A3243G mutation on haplogroup J in patients (p = 0.01, OR = 0.26, C.I. 95%: 0.08–0.83), suggesting that might be due to a strong negative selection at the embryo or germ line stages. Conclusion: Thus, our study supports the existence of mutational hotspot on mtDNA and a "haplogroup J paradox," a haplogroup that may increase the expression of mtDNA pathogenic mutations, but also be beneficial in certain environmental contexts

An update on nerve biopsy.

International audienceIndications for nerve biopsy have decreased during the last 20 years. For the most part, this is a result of progress in the application of molecular biologic diagnostic testing for genetic peripheral neuropathies (PNs) and the increasing use of skin biopsy. The latter is primarily used to evaluate small-fiber PN, although it rarely discloses the specific etiology of a PN. Nerve biopsies are usually performed on either the sural or the superficial peroneal nerve, the latter in combination with removal of portions of the peroneus brevis muscle. The definite diagnosis of vasculitic lesions can be readily established on small paraffin-embedded nerve biopsy samples, although in some cases, the characteristic lesions are only apparent in muscle specimens. Other nerve specimens are routinely fixed in buffered glutaraldehyde and prepared for semithin sections and electron microscopy; frozen specimens are used for immunofluorescence studies. Electron microscopy is of great value in some cases of chronic inflammatory demyelinating polyneuropathies, monoclonal gammopathy, and storage diseases. Because more than 30 genes may be involved in genetic PNs, analysis of nerve lesions can direct the search for mutations in specific genes. Electron microscopy immunocytochemistry is mandatory in some cases of monoclonal dysglobulinemia. Thus, nerve biopsy is still of value in specific circumstances when it is performed by trained physicians and examined in a laboratory with expertise in nerve pathology

Robust single-molecule approach for counting autofluorescent proteins.

Using single-molecule microscopy, we present a method to quantify the number of single autofluorescent proteins when they cannot be optically resolved. This method relies on the measurement of the total intensity emitted by each aggregate until it photobleaches. This strategy overcomes the inherent problem of blinking of green fluorescent proteins. In the case of small protein aggregates, our method permits us to describe the mean composition with a precision of one protein. For aggregates containing a large number of proteins, it gives access to the average number of proteins gathered and a signature of the inhomogeneity of the aggregates' population. We applied this methodology to the quantification of small purified citrine multimers

Peripheral neuropathy and livedoid vasculopathy

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New evidence of a mitochondrial genetic background paradox: Impact of the J haplogroup on the A3243G mutation

Abstract Background The A3243G mutation in the tRNALeu gene (UUR), is one of the most common pathogenic mitochondrial DNA (mtDNA) mutations in France, and is associated with highly variable and heterogeneous disease phenotypes. To define the relationships between the A3243G mutation and mtDNA backgrounds, we determined the haplogroup affiliation of 142 unrelated French patients – diagnosed as carriers of the A3243G mutation – by control-region sequencing and RFLP survey of their mtDNAs. Results The analysis revealed 111 different haplotypes encompassing all European haplogroups, indicating that the 3243 site might be a mutational hot spot. However, contrary to previous findings, we observed a statistically significant underepresentation of the A3243G mutation on haplogroup J in patients (p = 0.01, OR = 0.26, C.I. 95%: 0.08–0.83), suggesting that might be due to a strong negative selection at the embryo or germ line stages. Conclusion Thus, our study supports the existence of mutational hotspot on mtDNA and a "haplogroup J paradox," a haplogroup that may increase the expression of mtDNA pathogenic mutations, but also be beneficial in certain environmental contexts.</p

PSD-95 expression controls l-DOPA dyskinesia through dopamine D1 receptor trafficking

International audienceL-DOPA-induced dyskinesia (LID), a detrimental consequence of dopamine replacement therapy for Parkinson's disease, is associated with an alteration in dopamine D1 receptor (D1R) and glutamate receptor interactions. We hypothesized that the synaptic scaffolding protein PSD-95 plays a pivotal role in this process, as it interacts with D1R, regulates its trafficking and function, and is overexpressed in LID. Here, we demonstrate in rat and macaque models that disrupting the interaction between D1R and PSD-95 in the striatum reduces LID development and severity. Single quantum dot imaging revealed that this benefit was achieved primarily by destabilizing D1R localization, via increased lateral diffusion followed by increased internalization and diminished surface expression. These findings indicate that altering D1R trafficking via synapse-associated scaffolding proteins may be useful in the treatment of dyskinesia in Parkinson's patients