An RNA-seq study in Friedreich ataxia patients identified hsa-miR-148a-3p as a putative prognostic biomarker of the disease.

Friedreich ataxia (FRDA) is a life-threatening hereditary ataxia; its incidence is 1:50,000 individuals in the Caucasian population. A unique therapeutic drug for FRDA, the antioxidant Omaveloxolone, has been recently approved by the US Food and Drug Administration (FDA). FRDA is a multi-systemic neurodegenerative disease; in addition to a progressive neurodegeneration, FRDA is characterized by hypertrophic cardiomyopathy, diabetes mellitus and musculoskeletal deformities. Cardiomyopathy is the predominant cause of premature death. The onset of FRDA typically occurs between the ages of 5 and 15. Given the complexity and heterogeneity of clinical features and the variability of their onset, the identification of biomarkers capable of assessing disease progression and monitoring the efficacy of treatments is essential to facilitate decision making in clinical practice. We conducted an RNA-seq analysis in peripheral blood mononuclear cells from FRDA patients and healthy donors, identifying a signature of small non-coding RNAs (sncRNAs) capable of distinguishing healthy individuals from the majority of FRDA patients. Among the differentially expressed sncRNAs, microRNAs are a class of small non-coding endogenous RNAs that regulate posttranscriptional silencing of target genes. In FRDA plasma samples, hsa-miR-148a-3p resulted significantly upregulated. The analysis of the Receiver Operating Characteristic (ROC) curve, combining the circulating expression levels of hsa-miR-148a-3p and hsa-miR-223-3p (previously identified by our group), revealed an Area Under the Curve (AUC) of 0.86 (95%, Confidence Interval 0.77-0.95; p-value < 0.0001). An in silico prediction analysis indicated that the IL6ST gene, an interesting marker of neuroinflammation in FRDA, is a common target gene of both miRNAs. Our findings support the evaluation of combined expression levels of different circulating miRNAs as potent epi-biomarkers in FRDA. Moreover, we found hsa-miR-148a-3p significantly over-expressed in Intermediate and Late-Onset Friedreich Ataxia patients' group (IOG and LOG, respectively) compared to healthy individuals, indicating it as a putative prognostic biomarker in this pathology.

Hsa-miR223-3p circulating level is upregulated in Friedreich's ataxia and inversely associated with HCLS1 associated protein X-1, HAX-1.

Frataxin (FXN) deficiency is responsible for Friedreich's ataxia (FRDA) in which, besides the characteristic features of spinocerebellar ataxia, two thirds of patients develop hypertrophic cardiomyopathy that often progresses to heart failure and premature death. Different mechanisms might underlie FRDA pathogenesis. Among them, the role of miRNAs deserves investigations. We carried out an miRNA PCR-array analysis of plasma samples of early-, intermediate- and late-onset FRDA groups, defining a set of 30 differentially expressed miRNAs. Hsa-miR223-3p is the only miRNA shared between the three patient groups and appears upregulated in all of them. The up-regulation of hsa-miR223-3p was further validated in all enrolled patients (n = 37, Fc = +2.3; P < 0.0001). Using a receiver operating characteristic curve analysis, we quantified the predictive value of circulating hsa-miR223-3p for FRDA, obtaining an area under the ROC curve value of 0.835 (P < 0.0001) for all patients. Interestingly, we found a significant positive correlation between hsa-miR223-3p expression and cardiac parameters in typical FRDA patients (onset < 25 years). Moreover, a significant negative correlation between hsa-miR223-3p expression and HAX-1 (HCLS1-associated protein X-1) at mRNA and protein level was observed in all FRDA patients. In silico analyses suggested HAX-1 as a target gene of hsa-miR223-3p. Accordingly, we report that HAX-1 is negatively regulated by hsa-miR223-3p in cardiomyocytes (AC16) and neurons (SH-SY5Y), which are critically affected cell types in FRDA. This study describes for the first time the association between hsa-miR223-3p and HAX-1 expression in FRDA, thus supporting a potential role of this microRNA as non-invasive epigenetic biomarker for FRDA.

Tracking longitudinal thalamic volume changes during early stages of SCA1 and SCA2.

PURPOSE: Spinocerebellar ataxia SCA1 and SCA2 are adult-onset hereditary disorders, due to triplet CAG expansion in their respective causative genes. The pathophysiology of SCA1 and SCA2 suggests alterations of cerebello-thalamo-cortical pathway and its connections to the basal ganglia. In this framework, thalamic integrity is crucial for shaping efficient whole-brain dynamics and functions. The aims of the study are to identify structural changes in thalamic nuclei in presymptomatic and symptomatic SCA1 and SCA2 patients and to assess disease progression within a 1-year interval. MATERIAL AND METHODS: A prospective 1-year clinical and MRI assessment was conducted in 27 presymptomatic and 23 clinically manifest mutation carriers for SCA1 and SCA2 expansions. Cross-sectional and longitudinal changes of thalamic nuclei volume were investigated in SCA1 and SCA2 individuals and in healthy participants (n = 20). RESULTS: Both SCA1 and SCA2 patients had significant atrophy in the majority of thalamic nuclei, except for the posterior and partly medial nuclei. The 1-year longitudinal evaluation showed a specific pattern of atrophy in ventral and posterior thalamus, detectable even at the presymptomatic stage of the disease. CONCLUSION: For the first time in vivo, our exploratory study has shown that different thalamic nuclei are involved at different stages of the degenerative process in both SCA1 and SCA2. It is therefore possible that thalamic alterations might significantly contribute to the progression of the disease years before overt clinical manifestations occur.

Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia.

BACKGROUND AND OBJECTIVES: Spinocerebellar ataxias (SCAs) are autosomal dominant disorders with extensive clinical and genetic heterogeneity. We recently identified a form of SCA transmitted with a digenic pattern of inheritance caused by the concomitant presence of an intermediate-length expansion in TATA-box binding protein gene (TBP40-46 ) and a heterozygous pathogenic variant in the Stip1-homologous and U-Box containing protein 1 gene (STUB1). This SCATBP/STUB1 represents the first example of a cerebellar disorder in which digenic inheritance has been identified. OBJECTIVES: We studied a large cohort of patients with SCATBP/STUB1 with the aim of describing specific clinical and neuroimaging features of this distinctive genotype. METHODS: In this observational study, we recruited 65 affected and unaffected family members from 21 SCATBP/STUB1 families and from eight families with monogenic SCA17. Their characteristics and phenotypes were compared with those of 33 age-matched controls. RESULTS: SCATBP/STUB1 patients had multi-domain dementia with a more severe impairment in respect to patient carrying only fully expanded SCA17 alleles. Cerebellar volume and thickness of cerebellar cortex were reduced in SCATBP/STUB1 compared with SCA17 patients (P = 0.03; P = 0.008). Basal ganglia volumes were reduced in both patient groups, as compared with controls, whereas brainstem volumes were significantly reduced in SCATBP/STUB1 , but not in SCA17 patients. CONCLUSIONS: The identification of the complex SCATBP/STUB1 phenotype may impact on diagnosis and genetic counseling in the families with both hereditary and sporadic ataxia. The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Italian cross-cultural adaptation of the patient-reported outcome measure of ataxia.

BACKGROUND: The patient-reported outcome measure of ataxia (PROM-Ataxia) is the first patient-reported questionnaire specifically developed for use in patients with cerebellar ataxia. The scale was recently designed and validated in English language, and it consists of 70 items encompassing all aspects associated with the patient experience, including physical and mental health and their consequences on activities of daily living. The aim of the study was to translate and culturally adapt into Italian the PROM-Ataxia questionnaire, before assessing its psychometric properties. METHODS: We translated and culturally adapted into Italian the PROM-Ataxia following the ISPOR TCA Task Force guidelines. The questionnaire was field tested via cognitive interviews with users. RESULTS: The Italian patients found that the questionnaire was complete, and no significant contents related to the physical, mental, and functional dimensions were missing. Some items were found redundant or ambiguous. Most of the identified issues pertained to semantic equivalence, and a few to conceptual and normative equivalence, while the questionnaire did not contain any idiomatic expression. CONCLUSIONS: The translation and cultural adaptation of the PROM-Ataxia questionnaire in the Italian patient population represent the pre-requisite for the subsequent psychometric validation of the scale. This instrument may be valuable for cross-country comparability that would allow the merging of the data in collaborative multinational research studies.

Frataxin deficiency in Friedreich's ataxia is associated with reduced levels of HAX-1, a regulator of cardiomyocyte death and survival.

Frataxin deficiency, responsible for Friedreich's ataxia (FRDA), is crucial for cell survival since it critically affects viability of neurons, pancreatic beta cells and cardiomyocytes. In FRDA, the heart is frequently affected with typical manifestation of hypertrophic cardiomyopathy, which can progress to heart failure and cause premature death. A microarray analysis performed on FRDA patient's lymphoblastoid cells stably reconstituted with frataxin, indicated HS-1-associated protein X-1 (HAX-1) as the most significantly upregulated transcript (FC = +2, P < 0.0006). quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) and western blot analysis performed on (I) HEK293 stably transfected with empty vector compared to wild-type frataxin and (II) lymphoblasts from FRDA patients show that low frataxin mRNA and protein expression correspond to reduced levels of HAX-1. Frataxin overexpression and silencing were also performed in the AC16 human cardiomyocyte cell line. HAX-1 protein levels are indeed regulated through frataxin modulation. Moreover, correlation between frataxin and HAX-1 was further evaluated in peripheral blood mononuclear cells (PBMCs) from FRDA patients and from non-related healthy controls. A regression model for frataxin which included HAX-1, group membership and group* HAX-1 interaction revealed that frataxin and HAX-1 are associated both at mRNA and protein levels. Additionally, a linked expression of FXN, HAX-1 and antioxidant defence proteins MnSOD and Nrf2 was observed both in PBMCs and AC16 cardiomyocytes. Our results suggest that HAX-1 could be considered as a potential biomarker of cardiac disease in FRDA and the evaluation of its expression might provide insights into its pathogenesis as well as improving risk stratification strategies.

Comorbidities in Friedreich ataxia: incidence and manifestations from early to advanced disease stages.

OBJECTIVES: Friedreich's ataxia (FA) is the most common hereditary ataxia, characterized by multisystemic manifestations including neurological, cardiological, and skeletal abnormalities. In this study, we aimed to analyze the incidences of disease-related and unrelated comorbidities occurring in different stages of the disease progression. METHODS: We analyzed longitudinal data from a 10-year prospective observational study in a cohort of 175 FA patients with disease onset < 25 years. We analyzed the time of diagnosis for the most frequently reported medical conditions, with respect to age and disease duration of each patient. RESULTS: In the early stage of the disease, scoliosis (53.3%), hypertrophic cardiomyopathy (46.7%), and pes cavus (33.3%) were the most frequently diagnosed conditions, sometimes occurring even before the onset of ataxia. Diabetes, bone fractures, and depression have the same incidence at all disease stages. In patients with > 20 years of disease duration, the most frequent complications were hearing and visual loss (20% and 26%), arrhythmias (16%), and psychosis (18%). Thirteen patients presented hallucinations/delusions in the absence of neurological acute events or mental illness predisposing to psychotic manifestations. Six of these patients fulfill the diagnostic criteria for Charles Bonnet syndrome. CONCLUSIONS: Incidence of FA-related medical conditions varies according to disease duration. In patients with very long disease duration, we observed an unexpectedly high incidence of visual and auditory pseudo-hallucinations that were not previously reported in FA patients. We hypothesized that these late complications may be possibly related to the severe sensory deafferentation syndrome observed in the advanced stages of FA disease.

Weight gain after subthalamic nucleus deep brain stimulation in Parkinson's disease is influenced by dyskinesias' reduction and electrodes' position.

Parkinson's disease is a common neurodegenerative disease that can be treated with pharmacological or surgical therapy. Subthalamic nucleus (STN) deep brain stimulation is a commonly used surgical option. A reported side effect of STN-DBS is weight gain: the aim of our study was to find those factors that determine weight gain, through one year-long observation of 32 patients that underwent surgery in our centre. During the follow-up, we considered: anthropometric features, hormonal levels, motor outcome, neuropsychological and quality of life outcomes, therapeutic parameters and electrodes position. The majority (84%) of our patients gained weight (6.7 kg in 12 months); more than a half of the cohort became overweight. At 12th month, weight gain showed a correlation with dyskinesias reduction, electrodes voltage and distance on the lateral axis. In the multivariate regression analysis, the determinants of weight gain were dyskinesias reduction and electrodes position. In this study, we identified dyskinesias reduction and distance between the active electrodes and the third ventricle as determining factors of weight gain after STN-DBS implantation in PD patients. The first finding could be linked to a decrease in energy consumption, while the second one could be due to a lower stimulation of the lateral hypothalamic area, known for its important role in metabolism and body weight control. Weight gain is a common finding after STN-DBS implantation, and it should be carefully monitored given the potential harmful consequences of overweight.

Accelerometer-based measures in Friedreich ataxia: a longitudinal study on real-life activity.

Quantitative measurement of physical activity may complement neurological evaluation and provide valuable information on patients' daily life. We evaluated longitudinal changes of physical activity in patients with Friedreich ataxia (FRDA) using remote monitoring with wearable sensors. We performed an observational study in 26 adult patients with FRDA and 13 age-sex matched healthy controls (CTR). Participants were asked to wear two wearable sensors, at non-dominant wrist and at waist, for 7 days during waking hours. Evaluations were performed at baseline and at 1-year follow-up. We analysed the percentage of time spent in sedentary or physical activities, the Vector Magnitude on the 3 axes (VM3), and average number of steps/min. Study participants were also evaluated with ataxia clinical scales and functional tests for upper limbs dexterity and walking capability. Baseline data showed that patients had an overall reduced level of physical activity as compared to CTR. Accelerometer-based measures were highly correlated with clinical scales and disease duration in FRDA. Significantly changes from baseline to l-year follow-up were observed in patients for the following measures: (i) VM3; (ii) percentage of sedentary and light activity, and (iii) percentage of Moderate-Vigorous Physical Activity (MVPA). Reduction in physical activity corresponded to worsening in gait score of the Scale for Assessment and Rating of Ataxia. Real-life activity monitoring is feasible and well tolerated by patients. Accelerometer-based measures can quantify disease progression in FRDA over 1 year, providing objective information about patient's motor activities and supporting the usefulness of these data as complementary outcome measure in interventional trials.

Myoclonus and Dystonia as Recurrent Presenting Features in Patients with the SCA21-Associated TMEM240 p.Pro170Leu Variant.

Background: Spinocerebellar ataxia 21 (SCA21) is a rare neurological disorder caused by heterozygous variants in TMEM240. A growing, yet still limited number of reports suggested that hyperkinetic movements should be considered a defining component of the disease. Case Series: We describe two newly identified families harboring the recurrent pathogenic TMEM240 p.Pro170Leu variant. Both index patients and the mother of the first proband developed movement disorders, manifesting as myoclonic dystonia and action-induced dystonia without co-occurring ataxia in one case, and pancerebellar syndrome complicated by action-induced dystonia in the other. We reviewed the literature on TMEM240 variants linked to hyperkinetic disorders, comparing our cases to described phenotypes. Discussion: Adding to prior preliminary observations, our series highlights the relevance of hyperkinetic movements as clinically meaningful features of SCA21. TMEM240 mutation should be included in the differential diagnosis of myoclonic dystonia and ataxia-dystonia syndromes.

Longitudinal changes of SARA scale in Friedreich ataxia: Strong influence of baseline score and age at onset.

BACKGROUND: The Scale for Assessment and Rating of Ataxia (SARA) is widely used in different types of ataxias and has been chosen as the primary outcome measure in the European natural history study for Friedreich ataxia (FA). METHODS: To assess distribution and longitudinal changes of SARA scores and its single items, we analyzed SARA scores of 502 patients with typical-onset FA (<25 years) participating in the 4-year prospective European FA Consortium for Translational Studies (EFACTS). Pattern of disease progression was determined using linear mixed-effects regression models. The chosen statistical model was re-fitted in order to estimate parameters and predict disease progression. Median time-to-change and rate of score progression were estimated using the Kaplan-Meier method and weighted linear regression models, respectively. RESULTS: SARA score at study enrollment and age at onset were the major predictive factors of total score progression during the 4-year follow-up. To a less extent, age at evaluation also influenced the speed of SARA progression, while disease duration did not improve the prediction of the statistical model. Temporal dynamics of total SARA and items showed a great variability in the speed of score increase during disease progression. Gait item had the highest annual progression rate, with median time for one-point score increase of 1 to 2 years. INTERPRETATION: Analyses of statistical properties of SARA suggest a variable sensitivity of the scale at different disease stages, and provide important information for population selection and result interpretation in future clinical trials.

Cognitive Reserve in Early Manifest Huntington Disease Patients: Leisure Time Is Associated with Lower Cognitive and Functional Impairment.

We focused on Cognitive Reserve (CR) in patients with early Huntington Disease (HD) and investigated whether clinical outcomes might be influenced by lifetime intellectual enrichment over time. CR was evaluated by means of the Cognitive Reserve Index questionnaire (CRIq), an internationally validated scale which includes three sections: education, working activity, and leisure time. The clinical HD variables were quantified at three different time points (baseline-t0, 1 year follow up-t1 and 2 years follow up-t2) as per the Unified Huntington's Disease Rating Scale (UHDRS), an internationally standardized and validated scale including motor, cognitive, functional and behavioral assays. Our sample consisted of 75 early manifest patients, withclinical stage scored according to the Total Functional Capacity (TFC) scale. Our correlational analysis highlighted a significant inverse association between CRIq leisure time (CRIq_LA) and longitudinal functional impairment (namely, the differential TFC score between t2 and t0 or ΔTFC) (p < 0.05), and the multidimensional progression of HD as measured by the composite UHDRS (cUHDRS, p < 0.01). CRIq_LA was significantly and positively associated with better cognitive performances at all time points (p < 0.05). Our results suggest that higher is the CRIq_LA, milder is the progression of HD in terms of functional, multidimensional and cognitive outcome.

Prediction of the disease course in Friedreich ataxia.

We explored whether disease severity of Friedreich ataxia can be predicted using data from clinical examinations. From the database of the European Friedreich Ataxia Consortium for Translational Studies (EFACTS) data from up to five examinations of 602 patients with genetically confirmed FRDA was included. Clinical instruments and important symptoms of FRDA were identified as targets for prediction, while variables such as genetics, age of disease onset and first symptom of the disease were used as predictors. We used modelling techniques including generalised linear models, support-vector-machines and decision trees. The scale for rating and assessment of ataxia (SARA) and the activities of daily living (ADL) could be predicted with predictive errors quantified by root-mean-squared-errors (RMSE) of 6.49 and 5.83, respectively. Also, we were able to achieve reasonable performance for loss of ambulation (ROC-AUC score of 0.83). However, predictions for the SCA functional assessment (SCAFI) and presence of cardiological symptoms were difficult. In conclusion, we demonstrate that some clinical features of FRDA can be predicted with reasonable error; being a first step towards future clinical applications of predictive modelling. In contrast, targets where predictions were difficult raise the question whether there are yet unknown variables driving the clinical phenotype of FRDA.

Multifaceted and Age-Dependent Phenotypes Associated With Biallelic PNPLA6 Gene Variants: Eight Novel Cases and Review of the Literature.

A wide spectrum of neurodegenerative diseases has been associated with pathogenic variants in the PNPLA6 (patatin-like phospholipase domain-containing protein 6) gene, including spastic paraplegia type 39, Gordon-Holmes, Boucher-Neuhauser, Oliver-Mc Farlane, and Laurence-Moon syndromes. These syndromes present variable and overlapping clinical symptoms, encompassing cerebellar ataxia, hypogonadotropic hypogonadism, chorioretinal dystrophy, spastic paraplegia, muscle wasting, peripheral neuropathy, and cognitive impairment. In the present study, we performed a wide genetic screening in 292 patients presenting with ataxia or spastic paraplegia using a probe-based customized gene panel, covering >200 genes associated with spinocerebellar diseases. We identified six novel and four recurrent PNPLA6 gene variants in eight patients (2.7%). Six patients presented an infantile or juvenile onset (age <18), and two patients had an adult onset. Cerebellar ataxia was observed in seven patients and spastic paraplegia in one patient. Progression of cerebellar symptoms was slow in all patients, who retained ambulation even after a mean disease duration of 15 years. Brain MRI showed cerebellar atrophy in 6/8 patients, more pronounced in superior and dorsal vermis lobules (I to VII). Additional clinical features included hypogonadotropic hypogonadism (5/8), growth hormone deficiency (2/8), peripheral axonal neuropathy (4/8), cognitive impairment (3/8), chorioretinal dystrophy (2/8), and bilateral vestibular areflexia with a reduced visual vestibule-ocular reflex (1/8). In accordance with previous studies, chorioretinal dystrophy was the most frequent presenting symptom in early onset patients, hypogonadotropic hypogonadism in juvenile onset cases, and cerebellar ataxia in adult patients. One patient had an initial clinical presentation compatible with Cerebellar Ataxia with Neuropathy and Vestibular Areflexia Syndrome (CANVAS), but no pathological expansions in the RFC1 gene. In conclusion, patients with PNPLA6 variants present a variable age of onset spanning from infancy to adulthood, and each clinical symptom has an age-dependent manifestation thus requiring a multi-systemic diagnostic approach. The description of patients presenting very late-onset cerebellar ataxia suggests that PNPLA6 genetic screening should also be considered in the diagnostic workout of adult cerebellar ataxia.

Bilateral Repetitive Transcranial Magnetic Stimulation With the H-Coil in Parkinson's Disease: A Randomized, Sham-Controlled Study.

Background: Pilot open-label application of high-frequency repetitive transcranial magnetic stimulation (rTMS) with H-coil in Parkinson's Disease (PD) have shown promising results. Objective: To evaluate safety and efficacy of high-frequency rTMS with H-coil in PD in a double-blind, placebo-controlled, randomized study. Methods: Sixty patients with PD were randomized into 3 groups: M1-PFC (real stimulation on primary motor-M1 and pre-frontal cortices-PFC), M1 (real rTMS on M1, sham on PFC), Sham (apparent stimulation). Primary outcome was baseline-normalized percent improvement in UPDRS part III OFF-therapy at the end of treatment (12 rTMS sessions, 4 weeks). Secondary outcomes were improvement in UPDRS part III sub-scores, timed tests, and neuropsychological tests. Statistical analysis compared improvement following real and sham stimulation at the end of the protocol using either a t-test or a Mann-Whitney test. Results: All patients tolerated the treatment and concluded the study. One patient from M1-PFC group was excluded from the analysis due to newly discovered uncontrolled diabetes mellitus. No serious adverse effect was recorded. At the end of treatment, patients receiving real rTMS (M1-PFC and M1 combined) showed significantly greater improvement compared to sham in UPDRS part III total score (p = 0.007), tremor subscore (p = 0.011), and lateralized sub-scores (p = 0.042 for the more affected side; p = 0.012 for the less affected side). No significant differences have been oserved in safety and efficacy outcomes between the two real rTMS groups. Notably, mild, not-distressing and transient dyskinesias occurred in 3 patients after real rTMS in OFF state. Conclusions: The present findings suggest that high-frequency rTMS with H-coil is a safe and potentially effective procedure and prompt larger studies for validation as add-on treatment in PD.

Interhemispheric balance in Parkinson's disease: a transcranial magnetic stimulation study.

BACKGROUND: Parkinson's disease (PD) is characterized by various changes in motor excitability. OBJECTIVE: To examine through Transcranial Magnetic Stimulation (TMS) cortical excitability, specifically addressing interhemispheric connections in PD. METHODS: Nineteen PD patients with a predominant involvement of the left hemibody (7 females, age 61.7 years,) and 13 controls (6 females, age 61.5 years) entered the study. Patients were subdivided into two groups (early and advanced) according to the time from PD diagnosis. Participants underwent evaluation of Resting Motor Threshold (RMT) and ipsilateral Silent Period (iSP), induced by suprathreshold TMS on the ipsilateral-M1, measured as suppression of voluntary EMG activity. Mirror Movements (MM) were EMG-recorded and scored, in three upper limb muscles, during unilateral voluntary hand movement. Patients were studied at baseline (OFF drug) and after acute levodopa challenge (ON). RESULTS: PD patients showed a general reduction in RMT vs controls (P < 0.01 for right and left hemisphere) in both drug conditions. Early PD had a significantly lower RMT over the right vs the left hemisphere (P = 0.027); this difference was no longer significant after levodopa. In early PD patients, MM were mainly observed in the right arm during voluntary activation of the left, more affected side both in OFF (P = 0.033) and in ON (P = 0.046). In PD, RMT of the left, less affected M1 was significantly correlated with the right lateralized motor score (P = 0.011; Spearman's coefficient = -0.585), as well as with disease duration. In PD patients, a shorter (P = 0.039) and smaller (P = 0.037) iSP was detected when the stimulus was applied to the worse M1 (right) compared with the contralateral side. This asymmetry was significant only OFF drug. In the PD group iSP-duration from the right, less affected APB was negatively correlated with the MM recorded from the same side during the voluntary movement of the worse side (Spearman's coefficient = -0.498; P = 0.035). CONCLUSIONS: Increased cortical motor excitability in PD, consistent with previous findings, is more evident in the worse hemisphere, particularly in early PD. Asymmetric motor involvement is also associated with excessive involuntary mirroring and defective interhemispheric inhibition, both unfavoring the more affected side. Altogether, these findings suggest that asymmetric motor involvement in PD, particularly in the earlier phases of the disease, affects the interhemispheric balance of cortical excitability, movement lateralization and transcallosal inhibition.