We have previously linked families with autosomal-dominant, late-onset parkinsonism to chromosome 12p11.2-q13.1 (PARK8). By high-resolution recombination mapping and candidate gene sequencing in 46 families, we have found six disease-segregating mutations (five missense and one putative splice site mutation) in a gene encoding a large, multifunctional protein, LRRK2 (leucine-rich repeat kinase 2). It belongs to the ROCO protein family and includes a protein kinase domain of the MAPKKK class and several other major functional domains. Within affected carriers of families A and D, six post mortem diagnoses reveal brainstem dopaminergic degeneration accompanied by strikingly diverse pathologies. These include abnormalities consistent with Lewy body Parkinson's disease, diffuse Lewy body disease, nigral degeneration without distinctive histopathology, and progressive supranuclear palsy-like pathology. Clinical diagnoses of Parkinsonism with dementia or amyotrophy or both, with their associated pathologies, are also noted. Hence, LRRK2 may be central to the pathogenesis of several major neurodegenerative disorders associated with parkinsonism.

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) cause late-onset Parkinson's disease (PD) with a clinical appearance indistinguishable from idiopathic PD. Initial studies suggest that LRRK2 mutations are the most common yet identified determinant of PD susceptibility, transmitted in an autosomal-dominant mode of inheritance. Herein, we characterize the LRRK2 gene and transcript in human brain and subclone the predominant ORF. Exogenously expressed LRRK2 protein migrates at Ϸ280 kDa and is present largely in the cytoplasm but also associates with the mitochondrial outer membrane. Familial-linked mutations G2019S or R1441C do not have an obvious effect on protein steady-state levels, turnover, or localization. However, in vitro kinase assays using full-length recombinant LRRK2 reveal an increase in activity caused by familial-linked mutations in both autophosphorylation and the phosphorylation of a generic substrate. These results suggest a gain-of-function mechanism for LRRK2-linked disease with a central role for kinase activity in the development of PD.dardarin ͉ parkinsonism ͉ PARK8

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) cause late-onset Parkinson's disease indistinguishable from idiopathic disease. The mechanisms whereby missense alterations in the LRRK2 gene initiate neurodegeneration remain unknown. Here, we demonstrate that seven of 10 suspected familial-linked mutations result in increased kinase activity. Functional and disease-associated mutations in conserved residues reveal the critical link between intrinsic guanosine triphosphatase (GTPase) activity and downstream kinase activity. LRRK2 kinase activity requires GTPase activity, whereas GTPase activity functions independently of kinase activity. Both LRRK2 kinase and GTPase activity are required for neurotoxicity and potentiate peroxide-induced cell death, although LRRK2 does not function as a canonical MAP-kinase-kinase-kinase. These results suggest a link between LRRK2 kinase activity and pathogenic mechanisms relating to neurodegeneration, further supporting a gain-of-function role for LRRK2 mutations.

Mutations in SCN2A, a gene encoding the voltage-gated sodium channel Nav1.2, have been associated with a spectrum of epilepsies and neurodevelopmental disorders. Here, we report the phenotypes of 71 patients and review 130 previously reported patients. We found that (i) encephalopathies with infantile/childhood onset epilepsies (≥3 months of age) occur almost as often as those with an early infantile onset (<3 months), and are thus more frequent than previously reported; (ii) distinct phenotypes can be seen within the late onset group, including myoclonic-atonic epilepsy (two patients), Lennox-Gastaut not emerging from West syndrome (two patients), and focal epilepsies with an electrical status epilepticus during slow sleep-like EEG pattern (six patients); and (iii) West syndrome constitutes a common phenotype with a major recurring mutation (p.Arg853Gln: two new and four previously reported children). Other known phenotypes include Ohtahara syndrome, epilepsy of infancy with migrating focal seizures, and intellectual disability or autism without epilepsy. To assess the response to antiepileptic therapy, we retrospectively reviewed the treatment regimen and the course of the epilepsy in 66 patients for which well-documented medical information was available. We find that the use of sodium channel blockers was often associated with clinically relevant seizure reduction or seizure freedom in children with early infantile epilepsies (<3 months), whereas other antiepileptic drugs were less effective. In contrast, sodium channel blockers were rarely effective in epilepsies with later onset (≥3 months) and sometimes induced seizure worsening. Regarding the genetic findings, truncating mutations were exclusively seen in patients with late onset epilepsies and lack of response to sodium channel blockers. Functional characterization of four selected missense mutations using whole cell patch-clamping in tsA201 cells-together with data from the literature-suggest that mutations associated with early infantile epilepsy result in increased sodium channel activity with gain-of-function, characterized by slowing of fast inactivation, acceleration of its recovery or increased persistent sodium current. Further, a good response to sodium channel blockers clinically was found to be associated with a relatively small gain-of-function. In contrast, mutations in patients with late-onset forms and an insufficient response to sodium channel blockers were associated with loss-of-function effects, including a depolarizing shift of voltage-dependent activation or a hyperpolarizing shift of channel availability (steady-state inactivation). Our clinical and experimental data suggest a correlation between age at disease onset, response to sodium channel blockers and the functional properties of mutations in children with SCN2A-related epilepsy.