Rare nonsynonymous variants in SORT1 are associated with increased risk for frontotemporal dementia.

We investigated the genetic role of sortilin (SORT1) in frontotemporal dementia (FTD). SORT1 is the neuronal receptor for granulin, encoded by the progranulin gene (GRN), a major causal gene for inherited FTD. In Belgian cohorts of 636 FTD patients and 1066 unaffected control individuals, we identified 5 patient-only nonsynonymous rare variants in SORT1. Rare variant burden analysis showed a significant increase in rare coding variants in patients compared to control individuals (p = 0.04), particularly in the ß-propeller domain (p = 0.04), with 2 rare variants located in the predicted binding site for GRN (p = 0.001). We extended these observations by analyzing 3 independent patient/control cohorts sampled in Spain, Italy, and Portugal by partners of the European Early-Onset Dementia Consortium, together with 1155 FTD patients and 1161 control persons. An additional 7 patient-only nonsynonymous variants were observed in SORT1 in European patients. Meta-analysis of the rare nonsynonymous variants in the Belgian and European patient/control cohorts revealed a significant enrichment in FTD patients (p = 0.006), establishing SORT1 as a genetic risk factor for FTD.

Clinical Evidence of Disease Anticipation in Families Segregating a C9orf72 Repeat Expansion.

Importance: Patients carrying a C9orf72 repeat expansion leading to frontotemporal dementia and/or amyotrophic lateral sclerosis have highly variable ages at onset of disease, suggesting the presence of modifying factors. Objective: To provide clinical-based evidence for disease anticipation in families carrying a C9orf72 repeat expansion by analyzing age at onset, disease duration, and age at death in successive generations. Design, Setting, and Participants: This cohort study was performed from June 16, 2000, to June 1, 2016, in 36 extended Belgian families in which a C9orf72 repeat expansion was segregating. The generational effect on age at onset, disease duration, and age at death was estimated using a mixed effects Cox proportional hazards regression model, including random-effects terms for within-family correlation and kinship. Time until disease onset or last examination, time from disease onset until death or last examination, or age at death was collected for for 244 individuals (132 proven or obligate C9orf72 carriers), of whom 147 were clinically affected (89 proven or obligate C9orf72 carriers). Main Outcomes and Measures: Generational effect on age at onset, disease duration, and age at death. Results: Among the 111 individuals with age at onset available (66 men and 45 women; mean [SD] age, 57.2 [9.1] years), the mean (SD) age at onset per generation (from earliest-born to latest-born generation) was 62.5 (8.3), 57.1 (8.2), 54.6 (10.2), and 49.3 (7.5) years. Censored regression analysis on all affected and unaffected at-risk relatives confirmed a decrease in age at onset in successive generations (P < .001). No generational effect was observed for disease duration or age at death. Conclusions and Relevance: The clinical data provide supportive evidence for the occurrence of disease anticipation in families carrying a C9orf72 repeat expansion by means of a decrease in age at onset across successive generations. This finding may help clinicians decide from which age onward it may be relevant to clinically follow presymptomatic individuals who carry a C9orf72 repeat expansion.

Safety and efficacy of natalizumab in Belgian multiple sclerosis patients: subgroup analysis of the natalizumab observational program.

Natalizumab (Tysabri(®)) is highly efficacious in controlling disease activity in relapsing multiple sclerosis (MS) patients. As it is one of the more recent therapies for MS, there remains a need for long-term safety and efficacy data of natalizumab in a clinical practice setting. The Tysabri observational program (TOP) is an open-label, multicenter, multinational, prospective observational study, aiming to recruit up to 6,000 patients with relapsing-remitting MS from Europe, Canada and Australia. The objectives of this study are to collect long-term safety and efficacy data on disease activity and disability progression. We report here the interim results of the 563 patients included in TOP between December 2007 and 2012 from Belgium. This patient cohort was older at baseline, had longer disease duration, higher neurological impairment, and a higher baseline annualized relapse rate, when compared to patients included in the pivotal phase III AFFIRM trial. Nevertheless, the efficacy of natalizumab was comparable. The annualized relapse rate on treatment was reduced by 90.70 % (p < 0.0001) with a cumulative probability of relapse of 26.87 % at 24 months. The cumulative probabilities of sustained disability improvement and progression at 24 months were 25.68 and 9.01 %, respectively. There were no new safety concerns over the follow-up period. Two cases of progressive multifocal leukoencephalopathy were diagnosed. Our results are consistent with other observational studies in the post-marketing setting.

Distinct clinical characteristics of C9orf72 expansion carriers compared with GRN, MAPT, and nonmutation carriers in a Flanders-Belgian FTLD cohort.

OBJECTIVE: To characterize patients with frontotemporal lobar degeneration (FTLD) with a repeat expansion mutation in the gene C9orf72, and to determine whether there are differences in the clinical presentation compared with FTLD carriers of a mutation in GRN or MAPT or with patients with FTLD without mutation. DESIGN: Patient series. SETTING: Dementia clinics in Flanders, Belgium. PATIENTS: Two hundred seventy-five genetically and phenotypically thoroughly characterized patients with FTLD. MAIN OUTCOME MEASURES: Clinical and demographic characteristics of 26 C9orf72 expansion carriers compared with patients with a GRN or MAPT mutation, as well as patients with familial and sporadic FTLD without mutation. RESULTS: C9orf72 expansion carriers developed FTLD at an early age (average, 55.3 years; range, 42-69 years), significantly earlier than in GRN mutation carriers or patients with FTLD without mutation. Mean survival (6.2 years; range, 1.5-17.0 years) was similar to other patient groups. Most developed behavioral variant frontotemporal dementia (85%), with disinhibited behavior as the prominent feature. Concomitant amyotrophic lateral sclerosis is a strong distinguishing feature for C9orf72 -associated FTLD. However, in most patients (73%), amyotrophic lateral sclerosis symptoms were absent. Compared with C9orf72 expansion carriers, nonfluent aphasia and limb apraxia were significantly more common in GRN mutation carriers. CONCLUSIONS: C9orf72 -associated FTLD most often presents with early-onset behavioral variant frontotemporal dementia with disinhibition as the prominent feature, with or without amyotrophic lateral sclerosis. Based on the observed genotype-phenotype correlations between the different FTLD syndromes and different genetic causes, we propose a decision tree to guide clinical genetic testing in patients clinically diagnosed as having FTLD.