Batzler, Anthony

Thiopurine drugs such as 6‐mercaptopurine (6‐MP) and 6‐thioguanine (6‐TG) are effective immunosuppressants and antineoplastic agents. We used a genome‐wide approach to identify genes that might contribute to individual variation in thiopurine response. Basal gene expression profiles, genome‐wide SNP data, and 6‐MP and 6‐TG Cell growth inhibition (GI50) values were generated for 200 Coriell Institute “Human Variation Panel” lymphoblastoid cell lines. Gene expression and genome‐wide SNPs were correlated with GI50 values to identify candidate genes that might contribute to thiopurine response. We identified 104 expression probes and 161 SNPs, as well as 315 gene probes and 579 SNPs that correlated significantly with GI50 values for 6‐MP and 6‐TG, respectively (P<10 −5 and 10 −6 , respectively). Three genes, CD83 , TXNDC13 and SNAP23 , contained SNPs that contributed significantly to both 6‐MP and 6‐TG cytotoxicity and were also significantly associated with expression levels (P<10 −4 ), suggesting a “three‐way model” involving genotype, gene expression and cytotoxicity. GBP5 , a gene with an expression level that correlated negatively with 6‐MP and 6‐TG GI50 values, sensitized leukemia cells when overexpressed. Functional studies of the remainder of the candidate genes are being performed. These results may enhance our ability to predict thiopurine response phenotypes. NIH GM28157.

AbstractBackgroundTau deposition is a key biological feature of Alzheimer’s disease (AD) that is closely related to cognitive impairment. However, it remains poorly understood why certain individuals may be more susceptible to tau accumulation while others are more resistant. The recent availability of tau positron emission tomography (tau‐PET) provides an opportunity to test the hypothesis that genetic factors are associated with differential tau deposition.MethodsWe performed a genome‐wide association study (GWAS) of tau‐PET on a sample of 754 individuals over age 50 (mean age 72.4 years, 54.6% men, 87.4% cognitively unimpaired) from the population‐based Mayo Clinic Study of Aging. Following genotyping with the Illumina GSA array and standard quality control, 515,206 single nucleotide polymorphisms (SNPs) were tested for association with entorhinal cortex 18F‐flortaucipir tau‐PET burden using linear regression under an additive genetic model and covarying for age and sex.ResultA genome‐wide significant association was identified for rs75546066, an intergenic SNP on chromosome 9 between MED27 (mediator complex subunit 27) and NTNG2 (netrin G2), with the minor (A) allele associated with lower tau burden (p=2.85 x 10‐8, β=‐0.48). Linkage disequilibrium and public expression quantitative trait loci (eQTL) data suggested a functional relationship between rs75546066 and NTNG2, the latter of which is highly expressed in the brain. In addition to this novel finding, three SNPs within MAPT (microtubule‐associated protein tau) displayed nominal associations to tau‐PET burden, including rs3785883 (p=0.04, β=0.07) which was previously associated with higher cerebrospinal fluid tau in an independent cohort. No associations with tau‐PET burden were identified for the APOE (apolipoprotein E) ɛ4 or ɛ2 alleles or for genotyped SNPs previously associated with AD in large case‐control studies.ConclusionTo our knowledge, this study represents the first reported neuroimaging GWAS of tau pathology. Our findings confirm the association of MAPT with tau burden and nominate the rs75546066‐NTNG2 locus as a novel potential protective influence against tau pathology which warrants further functional characterization. Our data also supports the inference that tau accumulation may have a genetic architecture distinct from APOE and other known AD susceptibility genes, which may have implications for improved risk stratification and therapeutic targeting models.