Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

A two-hybrid screening of human Tau protein: interactions with Alu-derived domain

The microtubule associated protein tau has been implicated in several neurodegenerative diseases, grouped as tauopathies. To search for tau-associated proteins, the two-hybrid system was used with tau as a bait and an adult human brain cDNA library as a source of putative interacting proteins. We have identified two positive clones consisting of an Alu-derived amino acid sequence that binds to tau and show moderate homology with a motif found in several neuronal proteins related to neurodegenerative disorders. We have also demonstrated that the Alu-derived motif interacts in vitro with tau and may be involved in modulation of its phosphorylation. These findings suggest the existence of tau-binding proteins that are able to bind to tau through their Alu-derived sequence in a direct way. The possible interaction of these proteins with tau could play a role in its cellular localization, regulate the amount of phosphorylated tau and also be involved in the pathological processes of tauopathies.Peer reviewe

Progressive supranuclear palsy and tau hyperphosphorylation in a patient with a C212Y parkin mutation

Autosomal recessive-juvenile parkinsonism (AR-JP) is one of the most common forms of familial Parkinson's disease (PD) and is related to mutations in the Park-2 gene, encoding for a protein ligase of ubiquitin, parkin. Different mutations located along the parkin gene have been observed in different AR-JP affected families, possibly interfering with the normal function of parkin and the proteasome system. Two cases of patients with AR-JP have been recently described presenting different homo- and heterozygous parkin mutations and limited tau pathology. We report here the case of a patient with clinical and pathological findings compatible with progressive supranuclear palsy (PSP), carrier of a single, heterozygous mutation of the parkin gene, and homozygous for the H1/H1 haplotype in the tau gene. Abnormal tau hyperphosphorylation has been observed in our patient brain samples, suggesting that a partial deficit of parkin, a protein with ubiquitin-ligase function, may trigger tau pathology in individuals with molecular genetic risk factors.Peer reviewe

Park2-null/tau transgenic mice reveal a functional relationship between parkin and tau

Mutations, haplotypes, and polymorphisms of tau and Park-2 genes constitute risk factors for developing tauopathies. In order to analyze the possible relationship between parkin and tau we generated a double-mutant mouse deficient for Park-2 expression and overexpressing a mutant tau protein (hTauVLW). Mice develop normally, although the median survival rate is considerably reduced with respect to wild type (45%). Aggregates of phosphorylated tau in neurons and reactive gliosis are quite abundant in cortex and hippocampus of these mice. Moreover, while in young transgenic mice the hTauVLW immunostained transgene product is observed in both cell bodies and dendrites, the hTauVLW mutant protein is only detected in the neuronal cell bodies when Park-2 gene is additionally deleted. Moreover, DNA fragmentation was detected by the TUNEL method, and cerebral atrophy is also present in these regions. The levels of phosphorylated tau and Hsp70 are increased in the double-mutant mice, while CHIP expression in hippocampus is lower when the Park-2 gene is deleted. Thus, the combination of Park-2 gene deletion with hTauVLW transgene overexpression in mice produces serious neuropathological effects, which reflect the existence of some relationship between both proteins.Peer reviewe

Sensibilidad de biomarcadores en el líquido cefalorraquídeo en enfermedades neurodegenerativas

Recent advances in the pathophysiology of Alzheimer�s disease has prompted the clinical development of biomarkers that would expand research in early diagnosis, rate of disease progression and monitoring the effect of therapies. Cerebrospinal fluid measures (CSF) of beta-amyloid 42, total tau and phospo- tau proteins have shown a high diagnostic accuracy in differenciating Alzheimer�s dementia from healthy controls, even at very early stages of the disease. Diagnostic accuracy of the biomarkers between Alzheimer�s disease and other dementia types is not as good, although the specificity of phospo-tau levels remains high. Clinical usefulness is limited by the invasiveness of the procedure, and by strict adhesion to a well-defined protocol and sample handling. The type of technical method for determination is not widely established, and variability between centres is high. Nevertheless, there is an important role of CSF biomarkers in selected cases, and in the research of timing the events of Alzheimer�s disease.El avance en el conocimiento de la biología de la enfermedad de Alzheimer ha favorecido el desarrollo clínico de biomarcadores que permitan un diagnóstico temprano, monitoricen la progresión y puedan servir parar la evaluación de terapias. Las determinaciones en el líquido cefalorraquídeo (LCR) de beta-amiloide 42 (BA42), proteína tau total y proteína tau fosforilada han mostrado tener un rendimiento diagnóstico elevado para diferenciar la demencia tipo Alzheimer respecto a controles, incluso en fases incipientes de la misma. El rendimiento respecto a otros tipos de enfermedades neurodegenerativas es más bajo, aunque la especificidad de la tau fosforilada se mantiene para diferenciar la demencia tipo Alzheimer de las otras. La aplicabilidad clínica se encuentra limitada por la necesidad de un procedimiento invasivo, y de un protocolo y adiestramiento técnico en la determinación de específicos. La tecnología de medida todavía no está estandarizada a nivel global y la variabilidad entre centros es alta. Sin embargo, en casos clínicos seleccionados y en la investigación de la patocronia de la enfermedad de Alzheimer, los biomarcadores de LCR juegan un papel importante

Iron overload, measured as serum ferritin, increases brain damage induced by focal ischemia and early reperfusion

High levels of iron, measured as serum ferritin, are associated to a worse outcome after stroke. However, it is not known whether ischemic damage might increase ferritin levels as an acute phase protein or whether iron overload affects stroke outcome. The objectives are to study the effect of stroke on serum ferritin and the contribution of iron overload to ischemic damage. Swiss mice were fed with a standard diet or with a diet supplemented with 2.5% carbonyl iron to produce iron overload. Mice were submitted to permanent (by ligature and by in situ thromboembolic models) or transient focal ischemia (by ligature for 1 or 3h). Treatment with iron diet produced an increase in the basal levels of ferritin in all the groups. However, serum ferritin did not change after ischemia. Animals submitted to permanent ischemia had the same infarct volume in the groups studied. However, in mice submitted to transient ischemia followed by early (1h) but not late reperfusion (3h), iron overload increased ischemic damage and haemorrhagic transformation. Iron worsens ischemic damage induced by transient ischemia and early reperfusion. In addition, ferritin is a good indicator of body iron levels but not an acute phase protein after ischemia.Depto. de Farmacología y ToxicologíaFac. de MedicinaTRUEpu

A new mutation of the τ gene, G303V, in early-onset familial progressive supranuclear palsy

[Background]: Progressive supranuclear palsy (PSP) is a clinicopathological syndrome related to τ deposits and in linkage disequilibrium with τ polymorphisms. Some rare familial PSP cases have been related to τ gene mutations.[Objective]: To present the clinical, pathological, and molecular data of one family with early-onset autosomal dominant PSP.[Design]: We performed clinical examinations, quantitative neurological tests, positron emission tomographic scans with fluorodopa F 18 and raclopride C 11, analysis of τ mutations, neuropathological examinations, and protein analyses on brain specimens.[Results]: Three family members had PSP confirmed by pathological features in the proband. A novel mutation of τ, G303V, was found in the proband and other family members. τ Isoforms with 4 microtubule-binding repeats were overexpressed in the proband brain.[Conclusions]: The G303V mutation of τ is associated with autosomal dominant PSP. Expression of 4 microtubule-binding repeat τ isoforms is increased in the proband.This study was supported by grant 08.5/0049/2001-2 from Comunidad Autónoma de Madrid, Madrid (Dr Sánchez); a grant from Lilly, Barcelona, Spain (Drs Perez and Avila); a grant from Fundacion Ramón Areces, Madrid (Dr de Yébenes); and a grant from the PSP Society, Washington, DC (Dr de Yébenes).Peer reviewe

Ferritin is associated with the aberrant tau filaments present in progressive supranuclear palsy

Tau-containing filaments purified from the brain of progressive supranuclear palsy (PSP) patients were isolated and characterized. These filaments co-purify with regular particles that biophysical and biochemical methods identified as ferritin shells. In vivo, brain tau accumulation in PSP co-localized with ferritin. These results suggest that ferritin/iron could modulate the formation of tau aggregates in PSP.Supported by the Spanish CICYT, Comunidad de Madrid, Fundacion Ferrer, and by a grant from the Society for Progressive Supranuclear Palsy.Peer reviewe