👤 Sarah Ross

Hypertrophic cardiomyopathy is a genetically heterogeneous myocardial disease with >1000 causal variants identified. Nonunique variants account for disease in many families. We sought to characterize nonunique variants in Australian families and determine whether they arise from common ancestral mutations or recurrent mutation events. Genetic test results of 467 index patients from apparently unrelated families with hypertrophic cardiomyopathy were evaluated. Causal variants were found in 185 of 467 (40%) families. Nonunique variants accounted for 122 of 185 (66%) families. The most common single genetic cause of hypertrophic cardiomyopathy is the recurrent The majority of families with a causal variant identified have a nonunique variant. Discovery of the genetic origins of human disease forms a fundamental basis for improved understanding of disease pathogenesis and phenotype development. Show less

We conducted a genome-wide association study of essential tremor, a common movement disorder characterized mainly by a postural and kinetic tremor of the upper extremities. Twin and family history studies show a high heritability for essential tremor. The molecular genetic determinants of essential tremor are unknown. We included 2807 patients and 6441 controls of European descent in our two-stage genome-wide association study. The 59 most significantly disease-associated markers of the discovery stage were genotyped in the replication stage. After Bonferroni correction two markers, one (rs10937625) located in the serine/threonine kinase STK32B and one (rs17590046) in the transcriptional coactivator PPARGC1A were associated with essential tremor. Three markers (rs12764057, rs10822974, rs7903491) in the cell-adhesion molecule CTNNA3 were significant in the combined analysis of both stages. The expression of STK32B was increased in the cerebellar cortex of patients and expression quantitative trait loci database mining showed association between the protective minor allele of rs10937625 and reduced expression in cerebellar cortex. We found no expression differences related to disease status or marker genotype for the other two genes. Replication of two lead single nucleotide polymorphisms of previous small genome-wide association studies (rs3794087 in SLC1A2, rs9652490 in LINGO1) did not confirm the association with essential tremor. Show less

Identifying rare genetic variants that drive the onset of disease is challenging, even before considering the additional genetic and environmental influences that likely exist in complex diseases. We recently published a study proposing a rare variant in the NR1H3 gene (p.R415Q, rs61731956) as responsible for the onset of multiple sclerosis (MS) in two multi-incident families (Wang et al., 2016). This publication has generated much discussion, and fortunately the possibility to validate a finding or prove it spurious can occur rapidly in genetic studies. All novel discoveries must be replicated, and best efforts should be made to ensure that these replications use the appropriate samples and approach, and provide the correct interpretation of the results. This Matters Arising Response paper addresses the Minikel and MacArthur (2016) and The International Multiple Sclerosis Genetics Consortium (2016) Matters Arising papers, published concurrently in Neuron. Show less

Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss and neuronal dysfunction. Despite the aggregation observed in some families, pathogenic mutations have remained elusive. In this study, we describe the identification of NR1H3 p.Arg415Gln in seven MS patients from two multi-incident families presenting severe and progressive disease, with an average age at onset of 34 years. Additionally, association analysis of common variants in NR1H3 identified rs2279238 conferring a 1.35-fold increased risk of developing progressive MS. The p.Arg415Gln position is highly conserved in orthologs and paralogs, and disrupts NR1H3 heterodimerization and transcriptional activation of target genes. Protein expression analysis revealed that mutant NR1H3 (LXRA) alters gene expression profiles, suggesting a disruption in transcriptional regulation as one of the mechanisms underlying MS pathogenesis. Our study indicates that pharmacological activation of LXRA or its targets may lead to effective treatments for the highly debilitating and currently untreatable progressive phase of MS. Show less

Carbohydrate response element-binding protein (ChREBP) is a transcription factor involved in hepatic lipogenesis. Its function is in part under the control of AMP-activated protein kinase (AMPK) and protein phosphatase 2A (PP2A). Given known effects of ethanol on AMPK and PP2A, it is plausible that ethanol might enhance fatty acid synthesis by increasing the activity of ChREBP. We hypothesized that another potential pathway of ethanol-induced hepatic steatosis is mediated by activation of ChREBP. The effects of ethanol on ChREBP were assessed in hepatoma cells and in C57BL/6J mice fed with the Lieber-DeCarli diet. When the cells were exposed to ethanol (50 mM) for 24 hours, the activity of a liver pyruvate kinase (LPK) promoter-luciferase reporter was increased by ∼4-fold. Ethanol feeding of mice resulted in the translocation of ChREBP from cytosol to the nucleus. Protein phosphatase 2A activity was increased in the liver of ethanol-fed mice by 22%. We found no difference in the levels of hepatic Xu-5-P between ethanol-fed mice and controls. Transfection of a constitutively active AMPK expression plasmid suppressed the basal activity of the LPK luciferase reporter and abolished the effect of ethanol on the reporter activity. However, transfection of rat hepatoma cells with a dominant-negative AMPK expression plasmid induced basal LPK luciferase activity by only ∼20%. The effect of ethanol on ChREBP was attenuated in the presence of okadaic acid, an inhibitor of PP2A. The effects of ethanol on AMPK and PP2A may result in activation of ChREBP, providing another potential mechanism for ethanol-induced hepatic steatosis. However, additional okadaic acid-insensitive effects appear to be important as well. Show less

Elucidating the genetic background of Parkinson disease and essential tremor is crucial to understand the pathogenesis and improve diagnostic and therapeutic strategies. A number of approaches have been applied including familial and association studies, and studies of gene expression profiles to identify genes involved in susceptibility to Parkinson disease. These studies have nominated a number of candidate Parkinson disease genes and novel loci including Omi/HtrA2, GIGYF2, FGF20, PDXK, EIF4G1 and PARK16. A recent notable finding has been the confirmation for the role of heterozygous mutations in glucocerebrosidase (GBA) as risk factors for Parkinson disease. Finally, association studies have nominated genetic variation in the leucine-rich repeat and Ig containing 1 gene (LINGO1) as a risk for both Parkinson disease and essential tremor, providing the first genetic evidence of a link between the two conditions. Although undoubtedly genes remain to be identified, considerable progress has been achieved in the understanding of the genetic basis of Parkinson disease. This same effort is now required for essential tremor. The use of next-generation high-throughput sequencing and genotyping technologies will help pave the way for future insight leading to advances in diagnosis, prevention and cure. Show less

Genetic variation in the leucine-rich repeat and Ig domain containing 1 gene (LINGO1) was recently associated with an increased risk of developing essential tremor (ET) and Parkinson disease (PD). Herein, we performed a comprehensive study of LINGO1 and its paralog LINGO2 in ET and PD by sequencing both genes in patients (ET, n=95; PD, n=96) and by examining haplotype-tagging single-nucleotide polymorphisms (tSNPs) in a multicenter North American series of patients (ET, n=1,247; PD, n= 633) and controls (n=642). The sequencing study identified six novel coding variants in LINGO1 (p.S4C, p.V107M, p.A277T, p.R423R, p.G537A, p.D610D) and three in LINGO2 (p.D135D, p.P217P, p.V565V), however segregation analysis did not support pathogenicity. The association study employed 16 tSNPs at the LINGO1 locus and 21 at the LINGO2 locus. One variant in LINGO1 (rs9652490) displayed evidence of an association with ET (odds ratio (OR) =0.63; P=0.026) and PD (OR=0.54; P=0.016). Additionally, four other tSNPs in LINGO1 and one in LINGO2 were associated with ET and one tSNP in LINGO2 associated with PD (P<0.05). Further analysis identified one tSNP in LINGO1 and two in LINGO2 which influenced age at onset of ET and two tSNPs in LINGO1 which altered age at onset of PD (P<0.05). Our results support a role for LINGO1 and LINGO2 in determining risk for and perhaps age at onset of ET and PD. Further studies are warranted to confirm these findings and to determine the pathogenic mechanisms involved. Show less

Recently, a variant in LINGO1 (rs9652490) was found to associate with increased risk of essential tremor. We set out to replicate this association in an independent case-control series of essential tremor from North America. In addition, given the clinical and pathological overlap between essential tremor and Parkinson disease, we also evaluate the effect of LINGO1 rs9652490 in two case-control series of Parkinson disease. Our study demonstrates a significant association between LINGO1 rs9652490 and essential tremor (P = 0.014) and Parkinson disease (P = 0.0003), thus providing the first evidence of a genetic link between both diseases. Show less

Apolipoprotein AV (apoAV) overexpression causes a decrease in plasma triglyceride (TG) levels, while deficiency of apoAV causes hypertriglyceridemia in both men and mice. However, contrary to what would be expected, plasma apoAV and TG levels in humans are positively correlated. To address this apparent paradox, we determined plasma apoAV levels in various mouse models with median TG levels ranging from 30 mg/dl in wild-type mice to 2089 mg/dl in glycosylphosphatidylinositol-anchored HDL binding protein 1-deficient mice. The data show that apoAV and TG levels are positively correlated in mice (r = +0.798, P < 0.001). In addition, we show that LPL gene transfer caused a simultaneous decrease in TG and apoAV in LPL-deficient mice. The combined data suggest that apoAV levels follow TG levels due to an intimate link between the apoAV molecule and TG-rich lipoproteins, comprising both secretion and removal of these lipoproteins. Taken together, the data suggest that higher plasma apoAV levels reflect an increased demand for plasma TG hydrolysis under normal physiological conditions. Show less

Bardet-Biedl syndrome is a heterogeneous disorder causing a spectrum of symptoms, including visual impairment, kidney disease, and hearing impairment. Evidence suggests that BBS gene mutations cause defective ciliogenesis and/or cilium dysfunction. Cochlear development is affected by BBS gene deletion, and adult Bbs6(-/-) and Bbs4(-/-) mice are hearing impaired. This study addresses BBS protein expression in the rodent cochlea, to gain a better understanding of its function in vivo. As predicted by in vitro studies, Bbs6 immunofluorescence was localized to the basal bodies of supporting cells and sensory hair cells prior to the onset of hearing. In adult tissue, Bbs6 expression persisted in afferent neurons, including within the dendrites that innervate hair cells, implicating Bbs6 in a sensory neuronal function. Bbs2, which interacts with Bbs6, was also localized to hair cell basal bodies and stereociliary bundles. Additionally, Bbs2 was expressed in supporting cells at their intercellular boundaries, in a spatiotemporal pattern mirroring the development of the microtubule network. Bbs4 localized to cilia and developing cytoplasmic microtubule arrays. Pcm-1, a microtubular protein that interacts with Bbs4 in vitro, showed a comparable expression. Depolymerization of microtubules in slice preparations of the living cochlea resulted in Bbs4 and Pcm-1 mislocalization. Pcm-1 was also mislocalized in Bbs4(-/-) mice. This suggests that Bbs4/Pcm-1 interactions may be important in microtubule-dependent cytoplasmic trafficking in vivo. In summary, our findings indicate that BBS proteins adopt a range of cellular distributions in vivo, not restricted to the centrosome or cilium, and so broaden the possible underlying pathomechanisms of the disease. Show less

Toxicogenomic studies are increasingly used to uncover potential biomarkers of adverse health events, enrich chemical risk assessment, and to facilitate proper identification and treatment of persons susceptible to toxicity. Current approaches to biomarker discovery through gene expression profiling usually utilize a single or few strains of rodents, limiting the ability to detect biomarkers that may represent the wide range of toxicity responses typically observed in genetically heterogeneous human populations. To enhance the utility of animal models to detect response biomarkers for genetically diverse populations, we used a laboratory mouse strain diversity panel. Specifically, mice from 36 inbred strains derived from Mus mus musculus, Mus mus castaneous, and Mus mus domesticus origins were treated with a model hepatotoxic agent, acetaminophen (300 mg/kg, ig). Gene expression profiling was performed on liver tissue collected at 24 h after dosing. We identified 26 population-wide biomarkers of response to acetaminophen hepatotoxicity in which the changes in gene expression were significant across treatment and liver necrosis score but not significant for individual mouse strains. Importantly, most of these biomarker genes are part of the intracellular signaling involved in hepatocyte death and include genes previously associated with acetaminophen-induced hepatotoxicity, such as cyclin-dependent kinase inhibitor 1A (p21) and interleukin 6 signal transducer (Il6st), and genes not previously associated with acetaminophen, such as oncostatin M receptor (Osmr) and MLX interacting protein like (Mlxipl). Our data demonstrate that a multistrain approach may provide utility for understanding genotype-independent toxicity responses and facilitate identification of novel targets of therapeutic intervention. Show less

To identify and characterize gene expression changes associated with photoreceptor cell loss in a Bbs4-knockout mouse model of retinal degeneration. Differential gene expression in the eyes of 5-month-old Bbs4(-/-) mice undergoing retinal degeneration were analyzed using gene microarrays (Affymetrix, Santa Clara, CA). Elevated ocular transcripts were confirmed by Northern blotting of RNA from Bbs4(-/-) and three additional mouse models of Bardet-Biedl Syndrome (BBS). TUNEL assays and transmission electron microscopy were used to study cell death and photoreceptor morphology in these mice. Three hundred fifty-four probes were differentially expressed in Bbs4(-/-) eyes compared with controls using a twofold cutoff. Numerous vision-related transcripts decreased because of photoreceptor cell loss. Increased expression of the stress response genes Edn2, Lcn2, Serpina3n, and Socs3 was noted at 5 months of age and as early as postnatal week 4 in the eyes of four BBS mouse model strains. A burst of apoptotic activity in the photoreceptor outer nuclear layer at postnatal week 2 and highly disorganized outer segments by postnatal weeks 4 to 6 was observed in all four strains. The specific loss of photoreceptors in Bbs4(-)(/)(-) mice allows us to identify a set of genes that are preferentially expressed in photoreceptors compared with other cell types found in the eye and is a valuable resource in the continuing search for genes involved in retinal disease. The molecular and morphologic changes observed in young BBS animal model eyes implies that BBS proteins play a critical, early role in establishing the correct structure and function of photoreceptors. Show less

The evolutionarily conserved planar cell polarity (PCP) pathway (or noncanonical Wnt pathway) drives several important cellular processes, including epithelial cell polarization, cell migration and mitotic spindle orientation. In vertebrates, PCP genes have a vital role in polarized convergent extension movements during gastrulation and neurulation. Here we show that mice with mutations in genes involved in Bardet-Biedl syndrome (BBS), a disorder associated with ciliary dysfunction, share phenotypes with PCP mutants including open eyelids, neural tube defects and disrupted cochlear stereociliary bundles. Furthermore, we identify genetic interactions between BBS genes and a PCP gene in both mouse (Ltap, also called Vangl2) and zebrafish (vangl2). In zebrafish, the augmented phenotype results from enhanced defective convergent extension movements. We also show that Vangl2 localizes to the basal body and axoneme of ciliated cells, a pattern reminiscent of that of the BBS proteins. These data suggest that cilia are intrinsically involved in PCP processes. Show less

BBS4 is one of several proteins that cause Bardet-Biedl syndrome (BBS), a multisystemic disorder of genetic and clinical complexity. Here we show that BBS4 localizes to the centriolar satellites of centrosomes and basal bodies of primary cilia, where it functions as an adaptor of the p150(glued) subunit of the dynein transport machinery to recruit PCM1 (pericentriolar material 1 protein) and its associated cargo to the satellites. Silencing of BBS4 induces PCM1 mislocalization and concomitant deanchoring of centrosomal microtubules, arrest in cell division and apoptotic cell death. Expression of two truncated forms of BBS4 that are similar to those found in some individuals with BBS had a similar effect on PCM1 and microtubules. Our findings indicate that defective targeting or anchoring of pericentriolar proteins and microtubule disorganization contribute to the BBS phenotype and provide new insights into possible causes of familial obesity, diabetes and retinal degeneration. Show less

Bardet-Biedl syndrome is a genetically and clinically heterogeneous disorder caused by mutations in at least seven loci (BBS1-7), five of which are cloned (BBS1, BBS2, BBS4, BBS6, and BBS7). Genetic and mutational analyses have indicated that, in some families, a combination of three mutant alleles at two loci (triallelic inheritance) is necessary for pathogenesis. To date, four of the five known BBS loci have been implicated in this mode of oligogenic disease transmission. We present a comprehensive analysis of the spectrum, distribution, and involvement in non-Mendelian trait transmission of mutant alleles in BBS1, the most common BBS locus. Analyses of 259 independent families segregating a BBS phenotype indicate that BBS1 participates in complex inheritance and that, in different families, mutations in BBS1 can interact genetically with mutations at each of the other known BBS genes, as well as at unknown loci, to cause the phenotype. Consistent with this model, we identified homozygous M390R alleles, the most frequent BBS1 mutation, in asymptomatic individuals in two families. Moreover, our statistical analyses indicate that the prevalence of the M390R allele in the general population is consistent with an oligogenic rather than a recessive model of disease transmission. The distribution of BBS oligogenic alleles also indicates that all BBS loci might interact genetically with each other, but some genes, especially BBS2 and BBS6, are more likely to participate in triallelic inheritance, suggesting a variable ability of the BBS proteins to interact genetically with each other. Show less

Activation of Wnt signaling through beta-catenin mutations contributes to the development of hepatocellular carcinoma (HCC) and hepatoblastoma (HB). To explore the contribution of additional Wnt pathway molecules to hepatocarcinogenesis, we examined beta-catenin, AXIN1 and AXIN2 mutations in 73 HCCs and 27 HBs. beta-catenin mutations were detected in 19.2% (14 out of 73) HCCs and 70.4% (19 out of 27) HBs. beta-catenin mutations in HCCs were primarily point mutations, whereas more than half of the HBs had deletions. AXIN1 mutations occurred in seven (9.6%) HCCs and two (7.4%) HBs. The AXIN1 mutations included seven missense mutations, a 1 bp deletion, and a 12 bp insertion. The predominance of missense mutations found in the AXIN1 gene is different from the small deletions or nonsense mutations described previously. Loss of heterozygosity at the AXIN1 locus was present in four of five informative HCCs with AXIN1 mutations, suggesting a tumor suppressor function of this gene. AXIN2 mutations were found in two (2.7%) HCCs but not in HBs. Two HCCs had both AXIN1 and beta-catenin mutations, and one HCC had both AXIN2 and beta-catenin mutations. About half the HCCs with AXIN1 or AXIN2 mutations showed beta-catenin accumulation in the nucleus, cytoplasm or membrane. Overall, these data indicate that besides the approximately 20% of HCCs and 80% of HBs with beta-catenin mutations contributing to hepatocarcinogenesis, AXIN1 and AXIN2 mutations appear to be important in an additional 10% of HCCs and HBs. Show less

The gene-poor human-specific Xq21.3/Yp11.2 block of homology exhibits 99% nucleotide identity, with the exception of an internal X-specific region containing the marker DXS214. This paper describes the characterization of a novel gene (PABPC5) from this X-specific subinterval that belongs to the poly(A)-binding protein gene family. The genomic structure of PABPC5 covers 4061 bp of an uninterrupted open reading frame (ORF) and a 5'UTR spanning across two exons and associated with a CpG island; the potential 382-amino-acid protein contains four RNA recognition motif domains. PABPC5 has 73% nucleotide identity with PABPC4 over 1801 bp of the ORF. At the protein level, 60% identity and 75% similarity are obtained in the comparison with human PABPC4, as well as human, mouse, and Xenopus PABPC1. RT-PCR indicates that PABPC5 is expressed in fetal brain and in a range of adult tissues. Conservation of the PABPC5 ORF and genomic structure is shown in primates and rodents. The close proximity of this gene to translocation breakpoints associated with premature ovarian failure makes it a potential candidate for this condition. Show less

Atrophin-1 contains a polyglutamine repeat, expansion of which is responsible for dentatorubral and pallidoluysian atrophy (DRPLA). The normal function of atrophin-1 is unknown. We have identified five atrophin-1 interacting proteins (AIPs) which bind to atrophin-1 in the vicinity of the polyglutamine tract using the yeast two-hybrid system. Four of the interactions were confirmed using in vitro binding assays. All five interactors contained multiple WW domains. Two are novel. The AIPs can be divided into two distinct classes. AIP1 and AIP3/WWP3 are MAGUK-like multidomain proteins containing a number of protein-protein interaction modules, namely a guanylate kinase-like region, two WW domains, and multiple PDZ domains. AIP2/WWP2, AIP4, and AIP5/WWP1 are highly homologous, each having four WW domains and a HECT domain characteristic of ubiquitin ligases. These interactors are similar to recently isolated huntingtin-interacting proteins, suggesting possible commonality of function between two proteins responsible for very similar diseases. Show less