Marna B. McKenzie

DNM3 and genetic modifiers of age of onset in LRRK2 Gly2019Ser parkinsonism: a genome-wide linkage and association study

BACKGROUND Leucine-rich repeat kinase 2 (LRRK2) mutation 6055G→A (Gly2019Ser) accounts for roughly 1% of patients with Parkinsons disease in white populations, 13-30% in Ashkenazi Jewish populations, and 30-40% in North African Arab-Berber populations, although age of onset is variable. Some carriers have early-onset parkinsonism, whereas others remain asymptomatic despite advanced age. We aimed to use a genome-wide approach to identify genetic variability that directly affects LRRK2 Gly2019Ser penetrance. METHODS Between 2006 and 2012, we recruited Arab-Berber patients with Parkinsons disease and their family members (aged 18 years or older) at the Mongi Ben Hamida National Institute of Neurology (Tunis, Tunisia). Patients with Parkinsons disease were diagnosed by movement disorder specialists in accordance with the UK Parkinsons Disease Society Brain Bank criteria, without exclusion of familial parkinsonism. LRRK2 carrier status was confirmed by Sanger sequencing or TaqMan SNP assays-on-demand. We did genome-wide linkage analysis using data from multi-incident Arab-Berber families with Parkinsons disease and LRRK2 Gly2019Ser (with both affected and unaffected family members). We assessed Parkinsons disease age of onset both as a categorical variable (dichotomised by median onset) and as a quantitative trait. We used data from another cohort of unrelated Tunisian LRRK2 Gly2019Ser carriers for subsequent locus-specific genotyping and association analyses. Whole-genome sequencing in a subset of 14 unrelated Arab-Berber individuals who were LRRK2 Gly2019Ser carriers (seven with early-onset disease and seven elderly unaffected individuals) subsequently informed imputation and haplotype analyses. We replicated the findings in separate series of LRRK2 Gly2019Ser carriers originating from Algeria, France, Norway, and North America. We also investigated associations between genotype, gene, and protein expression in human striatal tissues and murine LRRK2 Gly2019Ser cortical neurons. FINDINGS Using data from 41 multi-incident Arab-Berber families with Parkinsons disease and LRRK2 Gly2019Ser (150 patients and 103 unaffected family members), we identified significant linkage on chromosome 1q23.3 to 1q24.3 (non-parametric logarithm of odds score 2·9, model-based logarithm of odds score 4·99, θ=0 at D1S2768). In a cohort of unrelated Arab-Berber LRRK2 Gly2019Ser carriers, subsequent association mapping within the linkage region suggested genetic variability within DNM3 as an age-of-onset modifier of disease (n=232; rs2421947; haplotype p=1·07 × 10-7). We found that DNM3 rs2421947 was a haplotype tag for which the median onset of LRRK2 parkinsonism in GG carriers was 12·5 years younger than that of CC carriers (Arab-Berber cohort, hazard ratio [HR] 1·89, 95% CI 1·20-2·98). Replication analyses in separate series from Algeria, France, Norway, and North America (n=263) supported this finding (meta-analysis HR 1·61, 95% CI 1·15-2·27, p=0·02). In human striatum, DNM3 expression varied as a function of rs2421947 genotype, and dynamin-3 localisation was perturbed in murine LRRK2 Gly2019Ser cortical neurons. INTERPRETATION Genetic variability in DNM3 modifies age of onset for LRRK2 Gly2019Ser parkinsonism and informs disease-relevant translational neuroscience. Our results could be useful in genetic counselling for carriers of this mutation and in clinical trial design. FUNDING The Canada Excellence Research Chairs (CERC), Leading Edge Endowment Fund (LEEF), Don Rix BC Leadership Chair in Genetic Medicine, National Institute on Aging, National Institute of Neurological Disorders and Stroke, the Michael J Fox Foundation, Mayo Foundation, the Roger de Spoelberch Foundation, and GlaxoSmithKline.

Loss-of-Function and Gain-of-Function Mutations in KCNQ5 Cause Intellectual Disability or Epileptic Encephalopathy

KCNQ5 is a highly conserved gene encoding an important channel for neuronal function; it is widely expressed in the brain and generates M-type current. Exome sequencing identified de novo heterozygous missense mutations in four probands with intellectual disability, abnormal neurological findings, and treatment-resistant epilepsy (in two of four). Comprehensive analysis of this potassium channel for the four variants expressed in frog oocytes revealed shifts in the voltage dependence of activation, including altered activation and deactivation kinetics. Specifically, both loss-of-function and gain-of-function KCNQ5 mutations, associated with increased excitability and decreased repolarization reserve, lead to pathophysiology.

De novo FGF12 mutation in 2 patients with neonatal-onset epilepsy.

Objective: We describe 2 additional patients with early-onset epilepsy with a de novo FGF12 mutation. Methods: Whole-exome sequencing was performed in 2 unrelated patients with early-onset epilepsy and their unaffected parents. Genetic variants were assessed by comparative trio analysis. Clinical evolution, EEG, and neuroimaging are described. The phenotype and response to treatment was reviewed and compared to affected siblings in the original report. Results: We identified the same FGF12 de novo mutation reported previously (c.G155A, p.R52H) in 2 additional patients with early-onset epilepsy. Similar to the original brothers described, both presented with tonic seizures in the first month of life. In the first patient, seizures responded to sodium channel blockers and her development was normal at 11 months. Patient 2 is a 15-year-old girl with treatment-resistant focal epilepsy, moderate intellectual disability, and autism. Carbamazepine (sodium channel blocker) was tried later in her course but not continued due to an allergic reaction. Conclusions: The identification of a recurrent de novo mutation in 2 additional unrelated probands with early-onset epilepsy supports the role of FGF12 p.R52H in disease pathogenesis. Affected carriers presented with similar early clinical phenotypes; however, this report expands the phenotype associated with this mutation which contrasts with the progressive course and early mortality of the siblings in the original report.

Genetic Identification in Early Onset Parkinsonism among Norwegian Patients

An initial diagnosis of Parkinsons disease (PD) is challenging, especially in patients who have early onset and atypical disease. A genetic etiology for parkinsonism, when established, ends that diagnostic odyssey and may inform prognosis and therapy. The objective of this study was to elucidate the genetic etiology of parkinsonism in patients with early onset disease (age at onset <45 years).

Neurobehavioral characterization of adult-onset Alexander disease A family study

Alexander disease is a clinically heterogeneous condition associated with glial fibrillary acidic protein ( GFAP ) gene mutations initially described in infants, but juvenile and adult forms exist. Adult-onset Alexander disease (AOAD) has an insidious onset of symptoms localized largely to brainstem, but may also include cognitive dysfunction.

A.01 Targeted analysis of whole exome sequencing and genotype-phenotype correlation in epileptic encephalopathies

SE Buerki (Vancouver) EB Toyota (Vancouver) I Guella (Vancouver) M McKenzie (Vancouver) D Evans (Vancouver) S Adam (Vancouver) MI van Allen (Vancouver) C Boelman (Vancouver) G Horvath (Vancouver) CD Van Karnebeek (Vancouver) P Eydoux (Vancouver) L Huh (Vancouver) A Datta (Vancouver) KA Selby (Vancouver) A Michoulas (Vancouver) TN Nelson (Vancouver) MJ Farrer (Vancouver) MB Demos (Vancouver)* MB Connolly (Vancouver)*