Background and ObjectivesIdentifying genetic causes of dementia in patients visiting memory clinics is important for patient care and family planning. Traditional clinical selection criteria for genetic testing may miss carriers of pathogenic variants in dementia-related genes. This study aimed identify how many carriers we are missing and to optimize criteria for selecting patients for genetic counseling in memory clinics.MethodsIn this clinical cohort study, we retrospectively genetically tested patients during 2.5 years (2010-2012) visiting the Alzheimer Center Amsterdam, a specialized memory clinic. Genetic tests consisted of a 54-gene dementia panel, focusing on Class IV/V variants per American College of Medical Genetics and Genomics guidelines, including APP duplications and the C9ORF72 repeat expansion. We determined the prevalence of pathogenic variants and propose new eligibility criteria for genetic testing in memory clinics. The eligibility criteria were prospectively applied for 1 year (2021-2022), and results were compared with the retrospective cohort.ResultsGenetic tests were retrospectively performed in in 1,022 of 1,138 patients (90%) who consecutively visited the memory clinic. Among these, 1,022 patients analyzed (mean age 62.1 ± 8.9 years; 40.4% were female), 34 pathogenic variant carriers were identified (3.3%), with 24 being symptomatic. Previous clinical criteria would have identified only 15 carriers (44% of all carriers, 65% of symptomatic carriers). The proposed criteria increased identification to 22 carriers (62.5% of all carriers, 91% of symptomatic carriers). In the prospective cohort, 148 (28.7%) of 515 patients were eligible for testing under the new criteria. Of the 90 eligible patients who consented to testing, 13 pathogenic carriers were identified, representing a 73% increase compared with the previous criteria.DiscussionWe found that patients who visit a memory clinic and carry a pathogenic genetic variant are often not eligible for genetic testing. The proposed new criteria improve the identification of patients with a genetic cause for their cognitive complaints. In systems without practical or financial barriers to genetic testing, the new criteria can enhance personalized care. In other countries where the health care systems differs and in other genetic ancestry groups, the performance of the criteria may be different.

Dysfunction of the endolysosomal-autophagy network is emerging as an important pathogenic process in Alzheimer's disease. Mutations in the sorting receptor-encoding gene SORL1 cause autosomal-dominant Alzheimer's disease, and SORL1 variants increase risk for late-onset AD. To understand the contribution of SORL1 mutations to AD pathogenesis, we analyze the effects of a SORL1 truncating mutation on SORL1 protein levels and endolysosome function in human neurons. We find that truncating mutation results in SORL1 haploinsufficiency and enlarged endosomes in human neurons. Analysis of isogenic SORL1 wild-type, heterozygous, and homozygous null neurons demonstrates that, whereas SORL1 haploinsufficiency results in endosome dysfunction, complete loss of SORL1 leads to additional defects in lysosome function and autophagy. Neuronal endolysosomal dysfunction caused by loss of SORL1 is relieved by extracellular antisense oligonucleotide-mediated reduction of APP protein, demonstrating that PSEN1, APP, and SORL1 act in a common pathway regulating the endolysosome system, which becomes dysfunctional in AD.

BACKGROUND: Dementia in families can be caused by one genetic variant. Identifying these so-called monogenic causes of dementia is important, because it explains the origin of dementia in families and raises the possibility of predictive testing for relatives. Still, we do not know how frequent these monogenic causes are, due to strict selection criteria for DNA testing based on age at onset and a positive family history. We aimed to identify the mutation frequency of monogenetic dementia by screening a large, unselected cohort of patients from a memory clinic specialized in early onset dementia. METHOD: Between 1-1-2010 and 1-7-2012, 1,138 patients visited the Alzheimer Center Amsterdam and all patients underwent the same diagnostic trajectory (van der Flier et al 2018). Of these, 1,093 (96%) consented to research and donated blood. An additional 73 patients (7%) were excluded because suboptimal DNA quality. Whole exome sequencing and C9orf72-repeat length analysis was performed in the remaining 1,020 patients (90% of all patients). All variants in 54 dementia related genes were analysed and classified. C9orf72 repeat length >30 repeat units was considered pathogenic. Variants classified as likely pathogenic and pathogenic were considered a monogenic cause of dementia. RESULT: The average age at presentation was 62(±6SD) years and 419(41%) were female. We found a monogenic cause of dementia in 34 (3.4%) patients. The most frequently occurring (likely) pathogenic variants were found in the genes C9orf72, PSEN1, NOTCH3 and MAPT. These genes explained 65% of the (likely) pathogenic variants. The clinical characteristics of the patients screened positive; 50% were diagnosed with dementia and 50% had a first degree relative with dementia; and 40% had an age at presentation of <60 years and 44% was between 60 to 70 years, the remainder was older. Surprisingly, only 47% of the patients with a (likely) pathogenic variant fulfilled our current criteria (based on diagnosis, age and familial history) for offering diagnostic genetic testing (21% of patients). CONCLUSION: In our large unselected cohort of patients from a memory clinic specialized in early onset dementia, the majority of the patients with a monogenetic predisposition for dementia did not fulfill our current criteria for genetic testing.