Yes / Topoisomerase1 (TOP1)-mediated chromosomal breaks are endogenous sources of DNA damage that affect neuronal genome stability. Whether TOP1 DNA breaks are sources of genomic instability in Huntington's disease (HD) is unknown. Here, we report defective 53BP1 recruitment in multiple HD cell models, including striatal neurons derived from HD patients. Defective 53BP1 recruitment is due to reduced H2A ubiquitination caused by the limited RNF168 activity. The reduced availability of RNF168 is caused by an increased interaction with p62, a protein involved in selective autophagy. Depletion of p62 or disruption of the interaction between RNAF168 and p62 was sufficient to restore 53BP1 enrichment and subsequent DNA repair in HD models, providing new opportunities for therapeutic interventions. These findings are reminiscent to what was described for p62 accumulation caused by C9orf72 expansion in ALS/FTD and suggest a common mechanism by which protein aggregation perturb DNA repair signaling. / This work is funded by a Welcome Trust Investigator Award (103844), a Lister Institute of Preventative Medicine Fellowship (137661) and a UKIERI grant (DST/INT/UK/P-147/2016) to S.F.E.- K. JG is additionally funded by a Clinical PhD Fellowship from the Pathological Society of Great Britain and Ireland and the Jean Shanks Foundation (JSPS-CPHD-2018-01).

Located on the short arm of chromosome 4, there exists a gene, IT15, responsible for the trinucleotide CAG expansion involved in the autosomal dominant neurodegenerative disorder known as Huntington’s disease (HD). The brain region associated with the most atrophy, the striatum, leads to expression of severe motor dysfunction, the hallmark feature of HD. To a lesser degree, the cortex and hippocampus show earlier deterioration indicative of the cognitive deficits that occur prior to motor symptom onset. The brain regions associated with HD-induced neuronal death additionally selectively express the protein Rhes - the combination of Rhes and mutant huntingtin being cytotoxic. Using a 3-nitropropionic acid animal model of HD, we hypothesized that animals with preserved prenylation of Rhes would display cognitive and motor symptomology similar to genetic models of HD while animals administered statins or bisphosphonates would show inhibited Rhes prenylation and delayed cognitive symptoms. Experimental animals, however, did not perform differently than control animals on shallow water variants of the t-maze and MWM.

La maladie de Huntington (HD) est une maladie génétique neurodégénérative qui touche environ 6000 personnes en France. Les manifestations psychiatriques sont une des composantes majeures des symptômes précoces de la pathologie. Ainsi, des épisodes dépressifs parfois associés à de l’anxiété généralisée sont communément observés au cours des stades pré-symptomatiques de la maladie. On connaît mal à l’heure actuelle les raisons de cette prévalence élevée. L'allèle responsable de la maladie code une protéine appelée huntingtine (HTT) dont l'expansion polyglutaminique (polyQ) en N-terminal est plus longue que dans la HTT non pathogénique. La huntingtine est impliquée dans diverses fonctions cellulaires et notamment dans le transport et l’expression d’un facteur neurotrophique, le Brain-Derived Neurotrophic Factor (BDNF). Celui-ci est d’ailleurs connu pour son rôle dans la régulation des troubles de l’humeur, de la neurogénèse hippocampique chez l’adulte, ainsi que dans la réponse thérapeutique aux antidépresseurs. Nous avons émis l'hypothèse que la huntingtine, en plus de ses rôles connus dans le cortex et le striatum, puisse jouer également un rôle dans l'hippocampe. Ainsi, une altération du transport de BDNF dans l’hippocampe pourrait en partie expliquer les troubles de l’humeur observés chez les patients HD.Par une approche in vivo, en utilisant différents modèles de souris, nous avons ainsi démontré que la huntingtine stimule le trafic vésiculaire et la sécrétion de BDNF dans les neurones hippocampiques et que cette action peut être modulée par la mutation polyQ ou par le statut de phosphorylation de la protéine sur les sérines 1181 et 1201. Cela aboutit à des modifications des voies de signalisation (Akt, ERK, CREB) activées par le BDNF. Nous mettons également en évidence que la huntingtine sauvage est impliquée dans le soutien exercé par les neurones matures sur les nouveaux neurones, nécessaire à leur survie à long terme et à la formation d’une arborisation dendritique complexe. Le BDNF est l’intermédiaire idéal grâce à ses effets sur la neurogenèse hippocampique. Enfin, la huntingtine sauvage et ses formes mutées (polyQ et phosphorylation sur les sérines 1181 et 1201) sont impliquées dans le comportement anxio-dépressif des souris. / Huntington disease (HD) is a genetic neurodegenerative disorder that affects about 6,000 people in France. Psychiatric manifestations are an important component of the early symptoms of the disease. Indeed, depressive episodes sometimes associated with generalized anxiety are commonly observed during the pre-symptomatic stages of disease. Few information is available about the reasons for this high prevalence.The allele responsible for the disease encodes a protein called huntingtin (HTT) whose polyglutamine expansion (polyQ) in the N-terminal region is longer than in the non-pathogenic HTT. Huntingtin is involved in various cellular functions including the transport and the expression of a neurotrophic factor, the Brain-Derived Neurotrophic Factor (BDNF). This factor is also known for its role in the regulation of mood, adult hippocampal neurogenesis, and in the therapeutic response to antidepressants.We hypothesized that huntingtin, in addition to its known roles in the cortex and striatum, may play a role in the hippocampus. Thus, an impaired transport of BDNF in the hippocampus could partly explain the mood disorders observed in HD patients.By an in vivo approach using different mouse models, we demonstrated that huntingtin stimulates vesicular trafficking and secretion of BDNF in hippocampal neurons and that this action may be modulated by the polyQ mutation or by the phosphorylation status of the protein on serines 1181 and 1201. These lead to changes in signaling pathways (Akt, ERK, CREB) activated by BDNF.We also demonstrate that normal huntingtin is involved in the support provided by mature neurons to new neurons for their long-term survival and the formation of a complex dendritic arborization. BDNF is the ideal candidate to mediate these effects on hippocampal neurogenesis. Finally, normal huntingtin and its mutated forms (polyQ and phosphorylated on serines 1181 and 1201) are involved in anxiety and depressive-like phenotype in mice.

La maladie de Huntington (MH) est une affection neurodégénérative héréditaire dont la mutation conduit à une expansion anormale d’un segment polyglutamine dans la protéine Huntingtine (Htt). La Htt mutée, bien qu’ubiquitaire dans le cerveau, conduit à une neurodégénérescence préférentielle du striatum. Cette atteinte pourrait en partie s’expliquer par la présence de produits de gènes sélectivement exprimés dans le striatum. Le laboratoire étudie depuis plusieurs années l’implication potentielle de marqueurs moléculaires du striatum dans la vulnérabilité des neurones de cette structure cérébrale vis-à-vis de la Htt mutée. Durant ma thèse, j’ai étudié plus spécifiquement trois de ces marqueurs du striatum: l’ARN long intergénique non-codant Abhd11os et les protéines µ-crystalline (CRYM) et doublecortin-like kinase 3 (DCLK3). Une étude préliminaire avait montré l’effet neuroprotecteur de ces marqueurs du striatum contre la toxicité induite par un fragment court de la Htt mutée dans un modèle murin aigu de la MH. J’ai donc étudié plus en détails les caractéristiques de ces "modificateurs" de la MH, ainsi que les mécanismes moléculaires potentiels permettant d’expliquer leur effet neuroprotecteur dans un contexte de la MH. J’ai également mené une expérience de thérapie génique en surexprimant le marqueur striatal DCLK3 dans un modèle transgénique de la MH. Cette étude nous a permis de valider le haut potentiel thérapeutique de cette protéine.L’élucidation précise des mécanismes d’action de ces modificateurs de la MH reste encore à résoudre, mais plusieurs pistes sont maintenant possiblement envisagées par rapport à leurs caractéristiques moléculaires. Outre la découverte de candidats neuroprotecteurs qui pourrait permettre de développer de nouvelles cibles thérapeutiques, cette étude a permis d’envisager de nouvelles hypothèses permettant d’expliquer la vulnérabilité striatale dans la MH et de donner une vue d’ensemble des voies sur lesquelles il serait possible d’agir pour induire des effets neuroprotecteurs dans ce contexte. / Huntington’s disease (HD) is a neurodegenerative disorder caused by the mutation of huntingtin (Htt) gene, which leads to an abnormal polyglutamine expansion in the Htt protein.Whereas mutant Htt (mHtt) is ubiquitously expressed in the brain, it preferentially affects the striatum. Our hypothesis is that genes products selectively expressed in the striatum could be involved in the high vulnerability of the striatum. From this hypothesis, numerous teams studied “markers of the striatum”, that are genes product enriched in the striatum whose expression are up- or down-regulated in HD compared to healthy condition.During my thesis, I studied three of these striatal markers: the long intergenic non-coding RNA Abhd11os, and the two proteins µ-crystallin (CRYM) and doublecortin-like kinase 3 (DCLK3). A preliminary study from the laboratory has shown that these three markers have neuroprotective effects against a toxic fragment of mHtt in vivo. So, the aims of my thesis were to further characterize these three ill-defined disease modifiers and to better understand the putative molecular mechanisms underlying their neuroprotective effects against mHtt.I also conducted a translational study on DCLK3, whose results validate the high therapeutic potential of this protein.The elucidation of the mechanisms underlying the neuroprotective effects of these disease modifiers against mHtt toxicity will require further studies, but new trails can be envisioned, according to their characteristics. My study has enlightened new therapeutic targets and more globally gives an overview of molecular mechanisms to modulate to induce neuroprotective effects in this context, leading to new hypothesis explaining striatal vulnerability in HD.

Afin d’analyser le rôle de la plasticité striatale dans la perception temporelle, nous avons réalisé une étude comportementale et électrophysiologique d’un modèle rat transgénique de la maladie de Huntington impliquant la dégénérescence progressive du striatum. Pour ce faire, nous avons élaboré une étude longitudinale (4-15 mois) du suivi de la maladie de Huntington au niveau moteur, motivationnel et temporel, et une étude présymptomatique (4-5 mois) de l’estimation temporelle et électrophysiologique in vivo de la voie préfronto-striatale. Nous avons détecté un dysfonctionnement de la perception temporelle et de la plasticité synaptique de manière présymptomatique, suggérant une corrélation entre ces deux dysfonctionnements. En symptomatique, le comportement temporel discriminatif est plus fortement altéré, corrélat d’une dégénérescence du striatum. / In order to assess the role of striatal plasticity in temporal perception, we have realized a behavioral and electrophysiological study of a transgenic rat model for Huntington’s disease that implicates progressive neurodegeneration of the striatum. For that purpose, we have done a longitudinal study (4-15 months) of Huntington’s disease at a motor, motivational and temporal level, and a presymptomatic study (4-5 months) of temporal estimation and of in vivo electrophysiological prefronto-striatal pathway. We have detected a dysfunction in temporal perception as well as an alteration of synaptic plasticity at a presymptomatic stage, suggesting the existence of a correlation between those two dysfunctions. At a symptomatic stage, the temporal discriminative behavior is deeply altered, correlating with striatum degeneration.

Le gène NR4A2 est un membre de la super famille des récepteurs nucléaires qui sont des facteurs de transcription activés par un ligand, tel que hormone stéroïde, rétinoïde ou hormone thyroïdienne. Cependant au sein de cette super famille, un groupe de facteurs, dont NR4A2 fait parti, ne possèdent pas de ligand identifié, c’est pourquoi ils sont dits orphelins. Le récepteur NR4A2, qui est un gène à réponse immédiate, induit par différents stimuli, est largement exprimé dans le cerveau. La description de son expression pendant le développement chez la souris montre que sa distribution anatomique va de pair avec certains neurones à dopamine. Afin d’étudier sa fonction, des souris (NR4A2 -/-) ont été générées. L’analyse de ces souris a montrée que l’absence de ce gène altère le développement et le maintien des neurones dopaminergiques de la substance noire et de l’aire tegmentaire ventrale, ainsi que l’expression de plusieurs gènes marqueurs du phénotype dopaminergique. Ces résultats ont placés NR4A2, au rang des gènes d’intérêt dans l’étude de la neuro-dégénérescence des neurones dopaminergiques impliquée dans la maladie de Parkinson. Pourtant, la description de l’expression de ce facteur chez le poisson, montre, que bien qu’il soit exprimé dans des régions dopaminergiques, il est aussi largement exprimé dans des régions qui ne sont pas dopaminergiques. L’analyse de NR4A2 par perte de fonction transitoire chez le poisson Danio rerio, sujet de ce mémoire, a permit de mettre en évidence certains aspects inconnus des fonctions de ce récepteur nucléaire. Ainsi, le gène NR4A2 régule l’expression d’un gène inhibiteur de CDK et l’expression d’un inhibiteur de neurogenèse. Par ce biais NR4A2 régule l’expression de gènes dits proneuraux, car exprimés dans les progéniteurs des neurones. Ces gènes proneuraux sont connus pour participer à la spécification cellulaire, à la sous spécification et à la différenciation de plusieurs phénotypes neuronaux. Ainsi, le gène NR4A2 induit chez Danio rerio le phénotype dopaminergique, mais il participe aussi à l’induction du neuro-phénotype NPY, du neuro-phénotype sérotoninergique et du neuro-phénotype Gabaergique. Ces nouvelles données in vivo font de NR4A2 un acteur important de la neurogénèse dont le rôle s’avère beaucoup plus large que ce qui était supposé jusqu’à présent. / The gene NR4A2 is a member of the great family of the nuclear receptors which are factors of transcription activated by a ligand, such as hormone steroid, rétinoide or thyroid hormone. However within this great family, a group of factors, NR4A2 of which makes left, does not possess an identified ligand, this is why they are said orphans. The receptor NR4A2, an immediate early gene, induced by different stimuli, is widely expressed in the brain. The description of its expression during the development to the mouse shows that its anatomical distribution goes together with certain dopaminergics neurons. To study its function, mice (NR4A2-/-) were generated. The analysis of these mice showed that the absence of this gene alters the development and the preservation of dopaminergics neurons in substancia nigra and in ventral tegmental area, as well as the expression of several genes markers of the dopaminergic phenotype. These results placed NR4A2, to the rank of the genes of interest in the study of the neuro-degeneration of dopaminergics neurons involved in the Parkinson's disease. Nevertheless, the description of the expression of this factor in fish, shows, that although it is expressed in dopaminergics regions, it is also widely expressed in regions which are not dopaminergic. The analysis of NR4A2 by loss of function in the fish Danio rerio, the subject of this thesis, has allowed bringing to light certain unknown aspects of the functions of this orphan nuclear receptor. So, the gene NR4A2 regulates the expression of an inhibitive gene of CDK and the expression of an inhibitor of neurogenesis. By this way NR4A2 regulates the expression of said proneuraux genes, because expressed in neuron’s progenitors. These proneural genes are known to participate in the cellular specification, in sub-specification and in the differentiation of several neuronal phenotypes. So, the gene NR4A2 leads to the dopaminergic phenotype in Danio rerio, but it also participates in the induction of the neuro-phenotype NPY, the serotoninergic neuro-phenotype and the neuro-phenotype Gabaergique. These new in vivo data make of NR4A2 an important actor of the neurogenesis whose role turns out much wider than what was supposed until now.

Submitted by Marcos Anselmo (marcos.anselmo@unipampa.edu.br) on 2016-04-07T18:47:53Z No. of bitstreams: 1 Aline Alves Courtes.pdf: 830792 bytes, checksum: f4e235b098c3ac508c33359985b6608b (MD5) / Made available in DSpace on 2016-04-07T18:47:53Z (GMT). No. of bitstreams: 1 Aline Alves Courtes.pdf: 830792 bytes, checksum: f4e235b098c3ac508c33359985b6608b (MD5) Previous issue date: 2014-08-25 / A doença de Huntington (DH) é uma desordem neurodegenerativa, hereditária autossômica dominante, caracterizada por alterações motoras progressivas, distúrbios emocionais, movimentos involuntários anormais e demência, os quais podem ser atribuídos à morte de neurônios estriatais e corticais. Apesar de ser uma etiologia ainda não totalmente conhecida, tem-se sugerido que o estresse oxidativo contribua para o desenvolvimento dessa condição. Nesse contexto, o ácido 3- nitropropiônico (3-NP), um inibidor da enzima mitocondrial succinato desidrogenase (SDH), têm sido utilizado em modelos animais por desenvolver as características fenotípicas observadas na DH. De um modo geral, o efeito do 3-NP está relacionado a capacidade do mesmo em causar disfunção mitocondrial e gerar espécies reativas. Nesse cenário, a pesquisa por terapias em que se busque neutralizar os efeitos deletérios das espécies reativas são de grande importância. A Luehea divaricata (L. divaricata), popularmente conhecida no Brasil como açoita cavalo contêm numerosos polifenóis, os quais poderiam atuar como agentes neuroprotetores em estudos in vitro e in vivo de doenças neurodegenerativas. Diante do exposto, buscamos nesse estudo testar a hipótese que o extrato aquoso de L. divaricata pode exercer efeito antioxidante e neuroprotetor frente às alterações comportamentais e oxidativas induzidas pelo 3-NP em ratos. Nossos dados demonstraram que o 3-NP induziu os sintomas da DH, uma vez que provocou mudanças de comportamento, evidenciados pela diminuição da atividade locomotora no Campo Aberto e Rota Rod; bem como alterações oxidativas evidenciadas pelo aumento dos níveis de espécies reativas de oxigênio (ROS) e peroxidação lipídica; redução nos níveis de glutationa reduzida e na atividade da acetilcolinesterase. O extrato aquoso de L. divaricata preveniu as alterações comportamentais e oxidativas induzidas pelo tratamento com 3-NP, sugerindo possível efeito neuroprotetor da L. divaricata contra a toxicidade do 3-NP, o qual pode ser devido a suas propriedades antioxidantes. Consequentemente, a planta poderia ser utilizada como um agente terapêutico para a prevenção dos sintomas da DH. / Huntington's disease (HD) is a neurodegenerative disorder, autosomal dominant, characterized by progressive motor disorders, emotional disturbances, abnormal involuntary movements and dementia, which can be attributed to the death of striatal and cortical neurons. Although a etiology is not fully known, it has been suggested that oxidative stress contributes to the development of this condition. In this context, the 3-nitropropionic acid (3-NP), an inhibitor of the mitochondrial enzyme succinate dehydrogenase (SDH), have been used in animal models to develop the phenotypic characteristics observed in HD. In general, the effect of 3-NP associated with the same capacity to cause mitochondrial dysfunction and generating reactive species. In this scenario, the search for treatments that seek to neutralize the deleterious effects of reactive species are of great importance. Luehea divaricata (L. divaricata), popularly known in Brazil as “açoita cavalo” contain numerous polyphenols, which could act as neuroprotective agents in in vitro and in vivo neurodegenerative diseases. Given the above, this study sought to test the hypothesis that the aqueous extract of L. divaricata may exert antioxidant and neuroprotective effect front and behavioral changes induced by oxidative 3-NP in rats. These data demonstrate that the 3-NP induced the symptoms of HD, because changes in behavior caused evidenced by the decrease in locomotor activity in the Open Field and Rota Rod; and oxidative changes evidenced by increased levels of reactive oxygen species (ROS) and lipid peroxidation; reduction in the levels of reduced glutathione and acetylcholinesterase activity. The aqueous extract of L. divaricata was able to prevent the oxidative and behavioral changes induced by 3-NP treatment, suggesting the possible neuroprotective effect against 3-NP toxicity, which may be due to its antioxidant properties. Consequently, this plant could be used as a potential therapeutic for the prevention of HD-like simptoms.

Adolescence is a time when individuals begin to explore and examine psychological characteristics of the self in order to discover who they really are and how they fit in the social world in which they live. It is during this time of self-exploration that adolescents at risk for Huntington's Disease often learn of their risk status and witness the debilitating symptoms of the disease in their parents. Huntington Disease (HD) is an autosomal dominant neuropsychiatric disorder characterized by mid-life onset, involuntary movements, cognitive impairment, and depression. This dissertation investigated how adolescents experience living in a family with Huntington's Disease and therefore at risk for Huntington's Disease, and how this impacts their self-understanding and self-identity. The method of inquiry was based on a phenomenological approach. In-depth interviews were conducted with each of the adolescents. The data were analyzed using Van Manen's (1980) and Cochran and Claspell's (1987) format, resulting in an extraction of three themes. These themes are: (1) Naming the Legacy: Understanding and Misunderstanding; (2) Experiencing the Legacy: Huntington's Disease in Relation to Relationships; and (3) Integrating the Legacy: At the Crossroads of Self and Future Self. The analysis emphasizes that the at-risk adolescents' exploration of self-identity and future self was an individual process influenced by the cognitive, developmental, and socio-cultural contexts of the adolescents' lives. The process of learning about Huntington's Disease occurred through intuition and practical and experiential learning. The adolescents found support outside their family through friends and adult mentors. They engaged in complicated coping strategies and demonstrated a capacity for decision-making that displayed maturity beyond what would be expected for their age group. These findings led to specific recommendations for theory, research, and clinical practice in the area of the adolescent experience of HD. The research underscores the need for healthcare professionals to re-evaluate their view of adolescent autonomy and capacity for decision-making.

Medium spiny neurons (MSNs) play an important role in locomotion. Counterbalance between two MSN subtypes, enkephalin-positive and substance P-positive MSNs, is crucial for maintaining normal movement. Preferential degeneration of enkephalinergic MSNs in early stage Huntington’s disease (HD) contributes to abnormal involuntary movement called chorea. The reasons for this selective vulnerability are unknown. In vitro differentiation of pluripotent stem cells (PSCs) to neuronal cells is considered a potential approach for modelling neurodegenerative disorders including HD. Generation of PSC-derived enkephalinergic MSNs would be an ideal tool for dissecting their preferential degeneration. However, an enkephalinergic phenotype has never been reported in PSC-derived MSNs. We, therefore, have generated a mouse embryonic stem cell (mESC) reporter line that expresses enhanced yellow fluorescent protein (EYFP) when the cells are committed to an enkephalinergic fate. Characterisation of this mESC line via chimaera generation showed that all EYFP-positive cells were also enkephalin-positive. We have then optimised an enkephalinergic neuronal differentiation protocol using this ESC line. Interestingly, we found that a combination of Wnt inhibitor Dickkopf-related protein 1 (DKK1), sonic hedgehog (Shh) and brain-derived neurotrophic factor (BDNF), commonly used in addition to basal medium for deriving MSNs from PSCs, had a detrimental effect on enkephalin expression. Absence of these three factors, surprisingly, did not reduce the potential of ESCs to become MSNs nor did it affect the electrophysiological properties of ESC-derived MSNs. Further investigation revealed that Pre-pro-enkephalin is down-regulated in the presence of exogenous DKK1 and/or Shh but not in the presence of BDNF. We, therefore, propose that addition of exogenous DKK1 and Shh is unfavourable to derive enkephalinergic MSNs from mouse ESCs. These findings could be used to derive enkephalinergic MSNs in vitro allowing the disease in a dish approach for HD modelling.

La distribution en taille, la concentration, ou la séquence des fragments d’ADN circulants dans le sang sont autant d’informations analytiques exploitables pour les cliniciens ou les spécialistes de la biologie moléculaire. Par exemple, l’ADN circulant, issu de cellules tumorales, peut servir de biomarqueur pour la détection et le suivi du cancer. L’accès à ces informations est d’autant plus difficile que la quantité d’ADN dans l’échantillon est faible. En pratique, pour atteindre des niveaux de sensibilité adaptés, la détection et l’analyse de résidus d’ADN requiert le développement et l’association de technologies d’analyses de type électrophorèse aux techniques de la biologie moléculaire telles que l’amplification PCR. Dans la perspective de simplifier et d’accélérer les procédures, nous avons développé et optimisé µLAS, un système microfluidique pour la concentration, la séparation et la détection simultanée de l’ADN résiduel. µLAS a ensuite été appliqué au diagnostic de la maladie de Huntington et à l’analyse de l’ADN résiduel circulant dans le sang. La maladie de Huntington, causée par l’expansion de répétitions CAG/CTG sur le gène Huntingtin, est à l’origine d’une dégénérescence neurologique. Le diagnostic de la maladie de Huntington consiste à amplifier et à mesurer la taille de cette expansion. L’amplification de répétitions trinucléotidiques étant peu fiable, nous profitons de la sensibilité de µLAS, pour réduire le nombre de cycles d’amplification, et donc le temps d’analyse. Par ailleurs, pour l’analyse sensible de l’ADN circulant par µLAS, nous avons proposé une approche originale, visant à réduire les manipulations pré-analytiques de l’échantillon sanguin à une simple digestion enzymatique suivie d’une centrifugation. Enfin le développement d’une fonction de détection spécifique de séquence a été réalisée par concentration sélective d’une cible d’intérêt hybridée à une sonde. Cette approche qui utilise des sondes marquées en fluorescence en volume, a notamment fait l’objet d’un brevet. / DNA fragments are circulating in the bloodstream. Circulating DNA fragments size, concentration or sequence are analytical information for the clinician or the molecular biology specialists. For instance, circulating DNA, stem from tumoral cells, can serve as biomarkers for cancer detection and follow up. Collecting those information may be difficult for samples presenting minute amount of DNA. In practice, detecting and analyzing residual DNA, with the relevant level of sensitivity, ask for the development and the association of analytical technologies, such as electrophoresis, to molecular biology techniques, such as PCR amplification. In the prospect of simplifying and speeding up the processes, we have developed and optimized µLAS, a microfluidic system for the simultaneous concentration, separation and detection of residual DNA. Furthermore, µLAS has been applied to the diagnostic of Huntington’s disease and the analysis of residual DNA circulating in the bloodstream. Huntington’s disease, is caused by the expansion of CAG/CTG repeats on the Huntingtin gene, and provoke neurological degeneration. The diagnostic of Huntington’s disease consist in amplifying and measuring this expansion. As the amplification of trinucleotide repeat is far from reliable, we benefit from µLAS sensitivity to reduce the number of amplification cycles, and the time to result. Additionally, for the sensitive analysis of circulating DNA by µLAS, we have proposed an original approach, aiming to reduce the blood sample pre-analytical steps to a simple enzymatic digestion followed by a centrifugation step. Finally, the development of a function for the detection of specific sequences has been made by the selective concentration of a target of interest hybridized to a probe. This approach which use some probes fluorescently labelled in volume, has been patented.