Characterization of the genetic landscape of Alzheimer’s disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/‘proxy’ AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele.

Genetic discoveries of Alzheimer’s disease are the drivers of our understanding, and together with polygenetic risk stratification can contribute towards planning of feasible and efficient preventive and curative clinical trials. We first perform a large genetic association study by merging all available case-control datasets and by-proxy study results (discovery n = 409,435 and validation size n = 58,190). Here, we add six variants associated with Alzheimer’s disease risk (near APP, CHRNE, PRKD3/NDUFAF7, PLCG2 and two exonic variants in the SHARPIN gene). Assessment of the polygenic risk score and stratifying by APOE reveal a 4 to 5.5 years difference in median age at onset of Alzheimer’s disease patients in APOE ɛ4 carriers. Because of this study, the underlying mechanisms of APP can be studied to refine the amyloid cascade and the polygenic risk score provides a tool to select individuals at high risk of Alzheimer’s disease.

Deciphering the genetic landscape of Alzheimer disease (AD) is essential to define the pathophysiological pathways involved and to successfully translate genomics to potential tailored medical care. To generate the most complete knowledge of the AD genetics, we developed through the European Alzheimer Disease BioBank (EADB) consortium a discovery meta-analysis of genome-wide association studies (GWAS) based on a new large case-control study and previous GWAS (in total 39,106 clinically diagnosed cases, 46,828 proxy-AD cases and 401,577 controls) with the most promising signals followed-up in independent samples (18,063 cases and 23,207 controls). In addition to 34 known AD loci, we report here the genome-wide significant association of 31 new loci with the risk of AD. Pathway-enrichment analyses strongly indicated the involvement of gene sets related to amyloid and Tau, but also highlighted microglia, in which increased gene expression corresponds to more significant AD risk. In addition, we successfully prioritized candidate genes in the majority of our new loci, with nine being primarily expressed in microglia. Finally, we observed that a polygenic risk score generated from this new genetic landscape was strongly associated with the risk of progression from mild cognitive impairment (MCI) to dementia (4,609 MCI cases of whom 1,532 converted to dementia), independently of age and the APOE e4 allele.

A 68-year-old man presented with a 4-month history of progressive memory loss and mood disorders. Neurologic examination revealed severe impairment of attention and verbal skills, without motor and sensory deficits. His medical history included mild arterial hypertension, idiopathic partial epilepsy, and obsessive compulsive disorder.Brain MRI showed the presence of bilateral, asymmetric, swollen white matter lesions in the cerebral hemispheres, hyperintense in T2-weighted images, that partially involved the left frontal cortex (figure). On diffusion-weighted sequences, the white matter abnormalities were consistent with vasogenic edema. No pathologic contrast enhancement was present.Routine blood tests, inflammatory markers, autoantibodies, neoplastic markers, and paraneoplastic antibodies were within normal limits. CSF examination revealed increased level of proteins (152 mg/dL) and cell count (14 leukocyte/L), without intrathecal synthesis of oligoclonal bands. Bacterioscopic and virologic tests (including HIV and JCV) were negative, both on CSF and serum. Search for tumor or infection by total body CT scan was negative.Stereotactic biopsy of the left frontal white matter lesion showed gliosis without signs of infections or neoplasm.After the biopsy, the patient was treated with dexamethasone 24 mg/day IV for 20 days with marked clinical improvement. A control CSF analysis performed 3 months later was within normal limits (Ͻ1 leukocyte/ L, protein 27 mg/dL). Brain MRI demonstrated a reduction in number and extension of the white matter T2-hyperintense lesions (figure). T2*-weighted gradient echo images showed the presence of multiple microhemorrhages scattered over the entire cerebral cortex. No microbleeds were present in basal ganglia, thalami, and posterior fossa (figure).Diagnosis of probable cerebral amyloid angiopathy-related inflammation (CAA-ri) was made upon clinical and MRI findings, supported by the demonstration of APOE ⑀4 homozygosity.A search for A␤ deposits in brain tissue and vessel walls on the biopsy sample was negative; a possible explanation is the deep white matter target, with absence of cortex and leptomeninges in the specimen. The A␤ 1-42 protein in the CSF was reduced both in the first (129 pg/mL) and second (125 pg/mL) lumbar puncture compared to normal values (682-1,063 pg/mL). The A␤ 1-40 protein was also investigated (457 pg/mL in the first CSF; 238 pg/mL in the second); however, due to the large variability of this assay as reported in literature, the meaning of these values is unclear.We hypothesized a spontaneous autoimmune process against CNS A␤ proteins, and assessed the levels of anti-A␤ 1-40 and 1-42 autoantibodies in our patient's CSF, both before and after steroid treatment, compared to 6 age-matched controls (mean age: 63 Ϯ 19 years) and 4 patients with MS (mean age: 45 Ϯ 17 years). We used our ELISA, as described, 1 and detected a marked increase of anti-A␤ 1-40 and 1-42 autoantibodies in the CSF of our CAA-ri patient obtained prior to treatment compared to controls and ...

IMPORTANCE Juvenile amyotrophic lateral sclerosis (ALS) is a rare form of ALS characterized by age of symptom onset less than 25 years and a variable presentation.OBJECTIVE To identify the genetic variants associated with juvenile ALS. DESIGN, SETTING, AND PARTICIPANTSIn this multicenter family-based genetic study, trio whole-exome sequencing was performed to identify the disease-associated gene in a case series of unrelated patients diagnosed with juvenile ALS and severe growth retardation. The patients and their family members were enrolled at academic hospitals and a government research facility between March 1, 2016, and March 13, 2020, and were observed until October 1, 2020. Whole-exome sequencing was also performed in a series of patients with juvenile ALS. A total of 66 patients with juvenile ALS and 6258 adult patients with ALS participated in the study. Patients were selected for the study based on their diagnosis, and all eligible participants were enrolled in the study. None of the participants had a family history of neurological disorders, suggesting de novo variants as the underlying genetic mechanism. MAIN OUTCOMES AND MEASURESDe novo variants present only in the index case and not in unaffected family members. RESULTSTrio whole-exome sequencing was performed in 3 patients diagnosed with juvenile ALS and their parents. An additional 63 patients with juvenile ALS and 6258 adult patients with ALS were subsequently screened for variants in the SPTLC1 gene. De novo variants in SPTLC1 (p.Ala20Ser in 2 patients and p.Ser331Tyr in 1 patient) were identified in 3 unrelated patients diagnosed with juvenile ALS and failure to thrive. A fourth variant (p.Leu39del) was identified in a patient with juvenile ALS where parental DNA was unavailable. Variants in this gene have been previously shown to be associated with autosomal-dominant hereditary sensory autonomic neuropathy, type 1A, by disrupting an essential enzyme complex in the sphingolipid synthesis pathway.CONCLUSIONS AND RELEVANCE These data broaden the phenotype associated with SPTLC1 and suggest that patients presenting with juvenile ALS should be screened for variants in this gene.