O5‐04‐02: RARE CODING MUTATIONS ASSOCIATED WITH ALZHEIMER DISEASE AND OTHER DEMENTIAS (2018)

Much of the unexplained heritability of Alzheimer disease (AD) may be due to rare variants whose effects are not captured in genome-wide association studies. We applied a strategy focused on rare variants occurring only in cases or controls. The AD Sequencing Project performed whole-exome sequencing on non-Hispanic white elders (5617 AD cases, 4594 controls). In 110 genes previously associated with AD or dementia, minor alleles of rare variants occurring only in AD cases or controls were tabulated. Top findings were explored with bioinformatics analyses and protein homology modeling. NOTCH3 rs149307620 had the largest number of minor alleles in only AD cases (n=10). NOTCH3 has been associated with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a diagnostically distinct disorder from AD, marked by severe headaches in young adulthood and stroke and dementia later in life. A genetic link between AD and NOTCH3 has not been established, except for a single report of a distinct NOTCH3 mutation shared by several AD-affected members of one family. Seven cases with rs149307620 and available clinical or autopsy data displayed classic AD symptoms with progressive memory loss, moderate to severe amyloid and tau pathology at autopsy and no evidence of stroke or severe microvascular disease. The mutation is found in the EGF protein domain near the JAG1-NOTCH3 binding site. Previous studies showed JAG1-Notch signaling and subsequent hippocampal neurogenesis and astrogenesis is regulated by BACE1, a promising AD drug target. Protein modeling showed the AD NOTCH3 mutation displays quantitative changes in bonding whereas CADASIL NOTCH3 mutations display qualitative changes involving the gain or loss of Cysteine and di-sulfide bonding. TREM2 rs104894002 was a high disease impact mutation found in four AD cases. Rs104894002 has previously been reported to contribute to AD and was recently linked to Nasu-Hakola disease, an autosomal recessive disorder characterized by dementia and multifocal bone cysts. We are currently soliciting clinical data for these four subjects to assess pleiotropy related to this mutation We identified several novel rare variants predicted to have high impact on protein structure which may alter AD risk and be potential therapeutic targets. References: Cruchaga, Carlos, et al. “GWAS of Cerebrospinal Fluid Tau Levels Identifies Risk Variants for Alzheimer's Disease.” Neuron, vol. 78, no. 2, 2013, pp. 256-268. Fernández, Maria Victoria, et al. “Sorl1 Variants Across Alzheimer's Disease Cohorts In European Americans.” Alzheimers & Dementia, vol. 12, no. 7, 2016, https://doi.org/10.1016/j.jalz.2016.06.1756. Ghezzi, L. “Evidence of CNS ß-Amyloid deposition in Nasu-Hakola disease due to the TREM2 Q33X mutation.” Neurology, vol. 89, no. 24, 2017, pp. 2503-2505. 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Lu, Yanjun, et al. “TREM2 variants and risk of Alzheimer's disease: a meta-Analysis.” Neurological Sciences, vol. 36, no. 10, 2015, pp. 1881-1888., https://doi.org/10.1007/sl0072-015-2274-2. Scheltens, P. “Clinicopathological concordance and discordance in three monozygotictwin pairs with familial Alzheimers disease.” Journal of Neurology, Neurosurgery & Psychiatry, vol. 78, no. 10, 2007, pp. 1039- 1039., https://doi.org/10.1136/jnnp.2007.118562. Vardarajan, Badri N., et al. “Rare coding mutations identified by sequencing of Alzheimer disease genome-Wide association studies loci.” Annals of Neurology, vol. 78, no. 3, 2015, pp. 487-498., https://doi.org/10.1002/ana.24466 . Protein Homology Modeling for NOTCH3 rs149307620 mutation. Using Maestro software, we modeled the predicted wild type NOTCH3 region protein structure with an alanine amino acid at the site of rs149307620 in Figure 1a. Alanine is non-polar and so would not have any interactions. Figure 1b shows the predicted mutated NOTCH3 region protein structure containing rs149307620 with a threonine amino acid at the mutation. Threonine is polar and will form hydrogen bonds where possible. In the JAG1 ligand, at the site of JAG1-NOTCH3 binding, there is a polar arginine. Figure1c shows the predicted model of the mutated NOTCH3 region with JAG1. Possible hydrogen bonding of NOTCH3's threonine is seen with the yellow dotted lines with both JAG1's arginine and within the protein structure itself. In contrast, study of CADASIL mutations in NOTCH3 involve the loss or gain of a cysteine residue, which is slighly polar, disrupting di-sulfide bonding within the protein structure.