Standaert, David G.

OBJECTIVE Stereotactic radiosurgery (SRS) is an effective treatment for refractory tremor. However, the lack of reliable patient-specific targeting biomarkers leads to varying outcomes. Although connectomic-based targeting is commonly used in deep brain stimulation, its application in SRS is limited. This study aimed to develop a new targeting approach by using patient-specific structural connectivity to improve outcomes after SRS. METHODS The authors performed a retrospective study of patients in a prospective trial for frameless virtual-cone SRS on a linear accelerator for essential tremor or tremor-dominant Parkinson disease. The primary endpoint was percentage improvement in Fahn-Tolosa-Marin tremor rating scale scores contralateral to the treatment side. Probabilistic tractography assessed connectivity from each thalamic voxel to the primary motor cortex (M1), primary sensory cortex (S1), and supplemental motor area/premotor cortex (SMA/PMC). Group-level comparisons were conducted to evaluate the relationship between the sweet spot for maximum contralateral tremor improvement and areas maximally connected to M1, S1, and SMA/PMC. Multiple regression analysis assessed the relationship between the lesion centerpoint coordinates and the maximally connected voxel to M1, S1, and SMA/PMC at the individual level. RESULTS The analysis included 27 patients with a mean follow-up of 17.9 ± 11.1 months. The sweet spot for maximal contralateral tremor improvement at the group level was in the region most connected to M1 cortex. Smaller y-distances (anterior-posterior) from the lesion center to the M1 maximally connected voxel significantly correlated with tremor improvement at the single-subject level (p < 0.001). However, the authors found no significant correlation between the lesion y-coordinate and the maximally connected voxel to SMA/PMC and S1, nor between the x-distances from the lesions to the SMA/PMC, M1, and S1 voxels (p > 0.07). CONCLUSIONS This study demonstrates that patient-specific connectivity between the treatment target and M1 correlates with treatment outcomes. The authors’ approach provides a practical targeting method for SRS thalamotomy for tremor.

ABSTRACTMutations in leucine‐rich repeat kinase 2 (LRRK2) are found in a significant proportion of late‐onset Parkinson's disease (PD) patients. Elucidating the neuroanatomical localization of LRRK2 will further define LRRK2 function and the molecular basis of PD. Here, we utilize recently characterized monoclonal antibodies to evaluate LRRK2 expression in rodent brain regions relevant to PD. In both mice and rats, LRRK2 is highly expressed in the cortex and striatum, particularly in pyramidal neurons of layer V and in medium spiny neurons within striosomes. Overall, rats have a more restricted distribution of LRRK2 compared with mice. Mice, but not rats, show high levels of LRRK2 expression in the substantia nigra pars compacta. Expression of the pathogenic LRRK2‐G2019S protein from mouse bacterial artificial chromosome (BAC) constructs closely mimics endogenous LRRK2 distribution in the mouse brain. However, LRRK2‐G2019S expression derived from human BAC constructs causes LRRK2 to be expressed in additional neuron subtypes in the rat such as striatal cholinergic interneurons and the substantia nigra pars compacta. The distribution of LRRK2 from human BAC constructs more closely resembles descriptions of LRRK2 in humans and nonhuman primates. Computational analyses of DNA regulatory elements in LRRK2 show a primate‐specific promoter sequence that does not exist in lower mammalian species. These noncoding regions may be involved in directing neuronal expression patterns. Together, these studies will aid in understanding the normal function of LRRK2 in the brain and will assist in model selection for future studies. J. Comp. Neurol. 522:2465–2480, 2014. © 2014 Wiley Periodicals, Inc.

ABSTRACTMutations in leucine‐rich repeat kinase 2 (LRRK2) are found in a significant proportion of late‐onset Parkinson's disease (PD) patients. Elucidating the neuroanatomical localization of LRRK2 will further define LRRK2 function and the molecular basis of PD. Here, we utilize recently characterized monoclonal antibodies to evaluate LRRK2 expression in rodent brain regions relevant to PD. In both mice and rats, LRRK2 is highly expressed in the cortex and striatum, particularly in pyramidal neurons of layer V and in medium spiny neurons within striosomes. Overall, rats have a more restricted distribution of LRRK2 compared with mice. Mice, but not rats, show high levels of LRRK2 expression in the substantia nigra pars compacta. Expression of the pathogenic LRRK2‐G2019S protein from mouse bacterial artificial chromosome (BAC) constructs closely mimics endogenous LRRK2 distribution in the mouse brain. However, LRRK2‐G2019S expression derived from human BAC constructs causes LRRK2 to be expressed in additional neuron subtypes in the rat such as striatal cholinergic interneurons and the substantia nigra pars compacta. The distribution of LRRK2 from human BAC constructs more closely resembles descriptions of LRRK2 in humans and nonhuman primates. Computational analyses of DNA regulatory elements in LRRK2 show a primate‐specific promoter sequence that does not exist in lower mammalian species. These noncoding regions may be involved in directing neuronal expression patterns. Together, these studies will aid in understanding the normal function of LRRK2 in the brain and will assist in model selection for future studies. J. Comp. Neurol. 522:2465–2480, 2014. © 2014 Wiley Periodicals, Inc.