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

Noninvasive temperature estimation in tissue via ultrasound echo- shifts. Part I. Analytical model

Temperature changes in tissue, caused by high-intensity focused ultrasound, cause time shifts in the echoes that traverse the heated tissue. These time shifts are caused by thermally induced changes in the distribution of the velocity of sound and by thermal expansion within the tissue. Our analytical model relates these shifts to changes in temperature distribution. It is proposed that these relationships can be used as a method for the noninvasive estimation of temperature within the tissue. The model shows that the echo shifts depend mostly on changes in the mean velocity along the acoustical path of the echoes and that no explicit information about the shape of the velocity distribution is required. The effects of the tissue thermal expansion are small in comparison, but may be significant under certain conditions. The theory, as well as numerical simulations, also predicts that the time shifts have an approximately linear behavior as a function of temperature. This suggests that an empirical linear delay- temperature relationship can be determined for temperature prediction. It is also shown that, alternatively, the distribution of temperature in the tissue can be estimated from the distribution of echo delays along the acoustical path. In the proposed system, low-level pulse echoes are sampled during brief periods when the high-intensity ultrasonic irradiation is off, and thus linear acoustic behavior is assumed. The possibility of nonlinear aftereffects and other disturbances limiting this approach is discussed

Noninvasive temperature estimation in tissue via ultrasound echo- shifts. Part II. In vitro study

Time shifts in echo signals returning from a heated volume of tissue correlate well with the temperature changes. In this study the relationship between these time shifts (or delays) and the tissue temperature was investigated in excised muscle tissue (turkey breast) as a possible dosimetric method. Heat was induced by the repeated activation of a sharply focused high-intensity ultrasound beam. Pulse echoes were sent and received with a confocal diagnostic transducer during the brief periods when the high- intensity ultrasonic beam was inactive. The change in transit time between echoes collected at different temperatures was estimated using cross- correlation techniques. With spatial-peak temporal-peak intensities (I(SPTP)) of less than 950 W/cm2, the delay versus temperature relationship was fit to a linear equation with highly reproducible coefficients. The results confirmed that for spatial-peak temperature increases of ~10 °C, temperature-dependent changes in velocity were the single most important factor determining the observed delay, and a linear approximation could produce accurate temperature estimations. Nonlinear phenomena that occurred during the high-intensity irradiation had no significant effect on the measured delay. At I(SPTP) of 1115-2698 W/cm2, the delay-temperature relationship showed a similar monotonically decreasing pattern, but as the temperature peaked its slope gradually increased. This may reflect the curvilinear nature of the velocity-temperature relationship, but it may also be related to irreversible tissue modifications and to the use of the spatial-peak temperature to experimentally characterize the temperature changes. Overall, the results were consistent with theoretical predictions and encourage further experimental work to validate other aspects of the technique

Tissue temperature estimation in-vivo with pulse-echo

Part of Proceedings of the IEEE Ultrasonics Symposium, Volume 2Time-shifts between echoes from volumes of tissue heated with focused ultrasound has been shown to track temperature changes accurately in-vitro. In this study we report the application of this method in-vivo where motion and perfusion have an additional effect on the measured shifts. Motion was characterized by the time-shifts detected on an echo segment from a proximal non-heated tissue site and a correction was applied to minimize their effect. The delay vs. temperature relationship (δ(T)) was similar to that previously described in-vitro but parameter variations were larger. Unlike in-vitro, the mean dδ/dT during temperature increases differs some from that during the cooling phases. It is suggested that this behavior can be predicted from the characteristics of the irradiating transducer and the acoustic parameters of the tissue and incorporated to the delay detection procedure

Dependence of ultrasonic attenuation and absorption in dog soft tissues on temperature and thermal dose

The effect of temperature and thermal dose (equivalent minutes at 43 °C) on ultrasonic attenuation in fresh dog muscle, liver, and kidney in vitro, was studied over a temperature range from room temperature to 70 °C. The effect of temperature on ultrasonic absorption in muscle was also studied. The attenuation experiments were performed at 4.32 MHz, and the absorption experiments at 4 MHz. Attenuation and absorption increased at temperatures higher than 50 °C, and eventually reached a maximum at 65 °C. The rate of change of tissue attenuation as a function of temperature was between 0.239 and 0.291 Np m-1 MHz-1 °C-1 over the temperature range 50-65 °C. A change in attenuation and absorption was observed at thermal doses of 100-1000 min, where a doubling of these loss coefficients was observed over that measured at 37 °C, presumably the result of changes in tissue composition. The maximum attenuation or absorption was reached at thermal dosages on the order of 107 min. It was found that the rate at which the thermal dose was applied (i.e., thermal dose per min) plays a very important role in the total attenuation absorption. Lower thermal dose rates resulted in larger attenuation coefficients. Estimations of temperature- dependent absorption using a bioheat equation based thermal model predicted the experimental temperature within 2 °C