Impaired Isometric Force Matching in Upper and Lower Limbs Revealed by Quantitative Motor Assessments in Huntington's Disease.

BACKGROUND: Assessment of motor symptoms in Huntington's disease (HD) is based on the Unified-HD-Rating-Scale-Total-Motor-Score (UHDRS-TMS). Its categorical and rater-dependent nature reduces the ability to detect subtle changes and often placebo effects have been observed in trials. We have previously shown that impairments in isometric force matching can be detected by quantitative motor (Q-Motor) assessments of tongue protrusion forces (glossomotography) in HD. OBJECTIVE: We aimed to investigate whether similar impairments in isometric force matching can be detected in tasks assessing hand and foot force coordination and whether correlations with clinical measures and the disease burden score can be found. METHODS: Using a pre-calibrated force transducer, the ability of subjects to generate and maintain isometric forces at different target levels displayed on a monitor was assessed. Target forces applied in the hand were 1.5 and 5 Newton [N] and in feet 1, 5, and 10 N. Subjects with HD (n = 31) and age-matched controls (n = 22) were recruited from the HD out-patient clinic. RESULTS: All paradigms distinguished controls from HD. The static coefficient of variability (%) was the most robust measure across all matching tasks. Correlations with clinical measures, such as the UHDRS-TMS, TFC, and the DBS were found. CONCLUSIONS: Assessment of hand and foot force matching tasks was feasible and provided quantitative objective measures for severity of motor phenotype in HD. Since both upper and lower extremity motor function are relevant for everyday activities, these measures should be further assessed as candidates for developing functionally meaningful quantitative motor tasks.

Huntington's Disease (HD): Neurodegeneration of Brodmann's Primary Visual Area 17 (BA17).

Huntington's disease (HD), an autosomal dominantly inherited polyglutamine or CAG repeat disease along with somatomotor, oculomotor, psychiatric and cognitive symptoms, presents clinically with impairments of elementary and complex visual functions as well as altered visual-evoked potentials (VEPs). Previous volumetric and pathoanatomical post-mortem investigations pointed to an involvement of Brodmann's primary visual area 17 (BA17) in HD. Because the involvement of BA17 could be interpreted as an early onset brain neurodegeneration, we further characterized this potential primary cortical site of HD-related neurodegeneration neuropathologically and performed an unbiased estimation of the absolute nerve cell number in thick gallocyanin-stained frontoparallel tissue sections through the striate area of seven control individuals and seven HD patients using Cavalieri's principle for volume and the optical disector for nerve and glial cell density estimations. This investigation showed a reduction of the estimated absolute nerve cell number of BA17 in the HD patients (71,044,037 ± 12,740,515 nerve cells) of 32% in comparison with the control individuals (104,075,067 ± 9,424,491 nerve cells) (Mann-Whitney U-test; P < 0.001). Additional pathoanatomical studies showed that nerve cell loss was most prominent in the outer pyramidal layer III, the inner granular layers IVa and IVc as well as in the multiform layer VI of BA17 of the HD patients. Our neuropathological results in BA17 confirm and extend previous post-mortem, biochemical and in vivo neuroradiological HD findings and offer suitable explanations for the elementary and complex visual dysfunctions, as well as for the altered VEP observed in HD patients.

Huntington's disease: objective assessment of posture--a link between motor and functional deficits.

BACKGROUND: Postural deficits in Huntington's disease are linked to functional impairment. We investigated whether assessment of center-of-mass variability using posturography provides objective and quantitative measures that correlate to the severity of motor phenotype, functional measures, and genotype as assessed by a disease burden score (based on repeat length and age). In addition, we investigated whether withdrawing visual feedback facilitates the detection of postural deficits. METHODS: Using a force plate, the ability of symptomatic Huntington's disease patients (n = 34) and controls (n = 20) to stand as stably as possible was assessed in eyes-open and eyes-closed conditions. RESULTS: All posturographic measures (DISTANCE, VELOCITY, and SURFACE of centre-of-mass mobility) were increased in patients and correlated to (1) the UHDRS Total Motor Score, (2) the UHDRS Total Functional Capacity, (3) the UHDRS Functional Assessment Score, and (4) the disease burden score. Correlations to motor and functional measures were stronger when visual feedback was provided. CONCLUSIONS: Posturography may provide useful objective and quantitative measures of postural motor dysfunction in Huntington's disease.

Assessment of involuntary choreatic movements in Huntington's disease--toward objective and quantitative measures.

Objective measures of motor impairment may improve the sensitivity and reliability of motor end points in clinical trials. In Huntington's disease, involuntary choreatic movements are one of the hallmarks of motor dysfunction. Chorea is commonly assessed by subitems of the Unified-Huntington's Disease Rating Scale. However, clinical rating scales are limited by inter- and intrarater variability, subjective error, and categorical design. We hypothesized that assessment of position and orientation changes interfering with a static upper extremity holding task may provide objective and quantitative measures of involuntary movements in patients with Huntington's disease. Subjects with symptomatic Huntington's disease (n = 19), premanifest gene carriers (n = 15; Unified-Huntington's Disease Rating Scale total motor score ≤ 3), and matched controls (n = 19) were asked to grasp and lift a device (250 and 500 g) equipped with an electromagnetic sensor. While subjects were instructed to hold the device as stable as possible, changes in position (x, y, z) and orientation (roll, pitch, yaw) were recorded. These were used to calculate a position index and an orientation index, both depicting the amount of choreatic movement interfering with task performance. Both indices were increased in patients with symptomatic Huntington's disease compared with controls and premanifest gene carriers for both weights, whereas only the position index with 500 g was increased in premanifest gene carriers compared with controls. Correlations were observed with the Disease Burden Score based on CAG-repeat length and age and with the Unified-Huntington's Disease Rating Scale. We conclude that quantitative assessment of chorea is feasible in Huntington's disease. The method is safe, noninvasive, and easily applicable and can be used repeatedly in outpatient settings. A use in clinical trials should be further explored in larger cohorts and follow-up studies.

Grasping premanifest Huntington's disease - shaping new endpoints for new trials.

Future clinical trials in subjects with premanifest Huntington's disease (preHD) may depend on the availability of biomarkers. It was previously shown in symptomatic HD that, the grip force variability coefficient-of-variation (GFV-C) in a grasping paradigm was correlated to the Unified-Huntington's-Disease-Rating-Scale-Total-Motor-Score (UHDRS-TMS) and increased in a 3 year follow-up study. To further elucidate its potential as a biomarker, we investigated whether GFV-C is able to detect a motor phenotype in preHD and is correlated to the genotype assessed by a disease-burden-score. The ability of preHD (n = 15) and symptomatic HD subjects (n = 20) to maintain stable grip forces, while holding an object (250 g and 500 g), was measured and compared with the controls (n = 19). GFV-C was increased in preHD at 500 g, in symptomatic subjects at both weights and was correlated to the disease-burden-score and UHDRS-TMS. GFV-C may be a useful objective and quantitative marker of motor dysfunction across genetically diagnosed premanifest and symptomatic HD subjects.

Tongue force analysis assesses motor phenotype in premanifest and symptomatic Huntington's disease.

Motor symptoms in Huntington's Disease (HD) are commonly assessed by the Unified Huntington's Disease Rating Scale-Total Motor Score (UHDRS-TMS). However, the UHDRS-TMS is limited by interrater variability, its categorical nature, and insensitivity in premanifest subjects. More objective and quantitative measures of motor phenotype may complement the use of the UHDRS-TMS as outcome measure and increase the power and sensitivity of clinical trials. Deficits in tongue protrusion are well acknowledged in HD and constitute a subitem of the UHDRS-TMS. We, therefore, investigated whether objective and quantitative assessment of tongue protrusion forces (TPF) provides measures that (1) correlate to the severity of motor phenotype detected in the UHDRS-TMS in symptomatic HD, (2) detect a motor phenotype in premanifest HD gene-carriers, and (3) exhibit a correlation to the genotype as assessed by a disease burden score (based on CAG-repeat length and age). Using a precalibrated force transducer, the ability of premanifest gene carriers (n = 15) and subjects with symptomatic HD (n = 20) to generate and maintain isometric TPF at three target force levels (0.25, 0.5, and 1.0 N) was assessed and compared with age-matched controls (n = 20) in a cross-sectional study. Measures of variability of TPF and tongue contact time distinguished controls, premanifest, and symptomatic HD groups and correlated to the UHDRS-TMS and disease burden score, suggesting a strong genotype-phenotype correlation. Group distinction was most reliable at the lowest target force level. We conclude that assessment of TPF may be a useful objective and quantitative marker of motor dysfunction in premanifest and symptomatic HD.

Genetic analysis of candidate genes modifying the age-at-onset in Huntington's disease.

The expansion of a polymorphic CAG repeat in the HD gene encoding huntingtin has been identified as the major cause of Huntington's disease (HD) and determines 42-73% of the variance in the age-at-onset of the disease. Polymorphisms in huntingtin interacting or associated genes are thought to modify the course of the disease. To identify genetic modifiers influencing the age at disease onset, we searched for polymorphic markers in the GRIK2, TBP, BDNF, HIP1 and ZDHHC17 genes and analysed seven of them by association studies in 980 independent European HD patients. Screening for unknown sequence variations we found besides several silent variations three polymorphisms in the ZDHHC17 gene. These and polymorphisms in the GRIK2, TBP and BDNF genes were analysed with respect to their association with the HD age-at-onset. Although some of the factors have been defined as genetic modifier factors in previous studies, none of the genes encoding GRIK2, TBP, BDNF and ZDHHC17 could be identified as a genetic modifier for HD.

The S18Y polymorphism in the UCHL1 gene is a genetic modifier in Huntington's disease.

An expanded polyglutamine stretch in the huntingtin protein has been identified as the pathogenetic cause of Huntington's disease (HD). Although the length of the expanded polyglutamine repeat is inversely correlated with the age-at-onset, additional genetic factors are thought to modify the variance in the disease onset. As linkage analysis suggested a modifier locus on chromosome 4p, we investigated the functional relevance of S18Y polymorphism of the ubiquitin carboxy-terminal hydrolase L1 in 946 Caucasian HD patients. In this group, the allelic variation on locus S18Y is responsible for 1.1% of the variance in the HD age-at-onset, and the rare Y allele is associated with younger-aged cases.