We analyzed four families that presented with a similar condition characterized by congenital microcephaly, intellectual disability, progressive cerebral atrophy and intractable seizures. We show that recessive mutations in the ASNS gene are responsible for this syndrome. Two of the identified missense mutations dramatically reduce ASNS protein abundance, suggesting that the mutations cause loss of function. Hypomorphic Asns mutant mice have structural brain abnormalities, including enlarged ventricles and reduced cortical thickness, and show deficits in learning and memory mimicking aspects of the patient phenotype. ASNS encodes asparagine synthetase, which catalyzes the synthesis of asparagine from glutamine and aspartate. The neurological impairment resulting from ASNS deficiency may be explained by asparagine depletion in the brain, or by accumulation of aspartate/glutamate leading to enhanced excitability and neuronal damage. Our study thus indicates that asparagine synthesis is essential for the development and function of the brain but not for that of other organs.
The endoplasmic reticulum-associated degradation (ERAD) pathway is responsible for the translocation of misfolded proteins across the ER membrane into the cytosol for subsequent degradation by the proteasome. In order to understand the spectrum of clinical and molecular findings in a complex neurological syndrome, we studied a series of eight patients with inherited deficiency of N-glycanase 1 (NGLY1), a novel disorder of cytosolic ERAD dysfunction.
Whole-genome, whole-exome or standard Sanger sequencing techniques were employed. Retrospective chart reviews were performed in order to obtain clinical data.
All patients had global developmental delay, a movement disorder, and hypotonia. Other common findings included hypo- or alacrima (7/8), elevated liver transaminases (6/7), microcephaly (6/8), diminished reflexes (6/8), hepatocyte cytoplasmic storage material or vacuolization (5/6), and seizures (4/8). The nonsense mutation c.1201A>T (p.R401X) was the most common deleterious allele.
NGLY1 deficiency is a novel autosomal recessive disorder of the ERAD pathway associated with neurological dysfunction, abnormal tear production, and liver disease. The majority of patients detected to date carry a specific nonsense mutation that appears to be associated with severe disease. The phenotypic spectrum is likely to enlarge as cases with a more broad range of mutations are detected.
NGLY1; alacrima; choreoathetosis; seizures; liver disease
Next-gene ration sequencing is becoming the primary discovery tool in human genetics. There have been many clear successes in identifying genes that are responsible for Mendelian diseases, and sequencing approaches are now poised to identify the mutations that cause undiagnosed childhood genetic diseases and those that predispose individuals to more common complex diseases. There are, however, growing concerns that the complexity and magnitude of complete sequence data could lead to an explosion of weakly justified claims of association between genetic variants and disease. Here, we provide an overview of the basic workflow in next-generation sequencing studies and emphasize, where possible, measures and considerations that facilitate accurate inferences from human sequencing studies.
Human genetic variation contributes to differences in susceptibility to HIV-1 infection. To search for novel host resistance factors, we performed a genome-wide association study (GWAS) in hemophilia patients highly exposed to potentially contaminated factor VIII infusions.
Individuals with hemophilia A and a documented history of factor VIII infusions before the introduction of viral inactivation procedures (1979–1984) were recruited from 36 hemophilia treatment centers (HTCs), and their genome-wide genetic variants were compared with those from matched HIV-infected individuals. Homozygous carriers of known CCR5 resistance mutations were excluded. Single nucleotide polymorphisms (SNPs) and inferred copy number variants (CNVs) were tested using logistic regression. In addition, we performed a pathway enrichment analysis, a heritability analysis, and a search for epistatic interactions with CCR5 Δ32 heterozygosity.
A total of 560 HIV-uninfected cases were recruited: 36 (6.4%) were homozygous for CCR5 Δ32 or m303. After quality control and SNP imputation, we tested 1 081 435 SNPs and 3686 CNVs for association with HIV-1 serostatus in 431 cases and 765 HIV-infected controls. No SNP or CNV reached genome-wide significance. The additional analyses did not reveal any strong genetic effect.
Highly exposed, yet uninfected hemophiliacs form an ideal study group to investigate host resistance factors. Using a genome-wide approach, we did not detect any significant associations between SNPs and HIV-1 susceptibility, indicating that common genetic variants of major effect are unlikely to explain the observed resistance phenotype in this population.
Background & Aims
We studied the relationship between IL28B gene-related SNP rs12979860 and early viral kinetics (day 0–28) during peginterferon and ribavirin treatment, in 173 African Americans (AA) and 188 Caucasian Americans (CA) with HCV genotype 1.
We studied the relationship between IL28B 16 gene-related SNP rs12979860 and early viral kinetics (day 0–28) 17 during peginterferon and ribavirin treatment, in 171 African 18 Americans (AA) and 188 Caucasian Americans (CA) with HCV 19 genotype 1.
Compared to non-C/C genotypes, C/C was associated with greater declines in serum HCV RNA during phase 1 (day 0–2), phase 2 (day 7–28), and day 0–28 and higher response (undetected HCV RNA) rates at weeks 4 and 12 in AA and CA. A static phase and increases in HCV RNA from day 2 to 7 were more common in patients with non-C/C genotypes. C/C was also associated with higher week 24, 48, and 72 response rates in CA (p <0.01) but not in AA. At baseline, SNP genotype was the only independent predictor of phase 1; SNP genotype and phase 1 were independent predictors of phase 2 (p<0.001). There were no racial differences in HCV RNA declines during phase 1, day 2–7, phase 2, and day 0–28 with the same SNP genotype. AA with C/C and C/T genotypes had lower week 24, 48, and 72 (SVR) rates than did CA (p = 0.03). SNP C/C predicted higher SVR rates in AA and CA with high baseline HCV RNA (≥ 600,000 IU/ml), and in CA with ≥ 1 log10 IU/ml decrease in HCV RNA from day 0 to 28.
SNP rs12979860 is strongly associated with both phase 1 and phase 2 HCV RNA kinetics in AA and CA with HCV genotype 1.
IL28B gene; Hepatitis C virus; Viral kinetics; Single nucleotide polymorphism
The 12th International Meeting on Human Genome Variation and Complex Genome Analysis (HGV2011: Berkeley, California, USA, 8th–10th September 2011) was a stimulating workshop where researchers from academia and industry explored the latest progress, challenges, and opportunities in genome variation research. Key themes included progress beyond GWAS, variation in human populations, use of sequence data in medical settings, large-scale sequencing data analysis, and bioinformatics approaches to large datasets.
human variation; GWAS; SNP; medical genomics
A central challenge in interpreting personal genomes is determining which mutations most likely influence disease. Although progress has been made in scoring the functional impact of individual mutations, the characteristics of the genes in which those mutations are found remain largely unexplored. For example, genes known to carry few common functional variants in healthy individuals may be judged more likely to cause certain kinds of disease than genes known to carry many such variants. Until now, however, it has not been possible to develop a quantitative assessment of how well genes tolerate functional genetic variation on a genome-wide scale. Here we describe an effort that uses sequence data from 6503 whole exome sequences made available by the NHLBI Exome Sequencing Project (ESP). Specifically, we develop an intolerance scoring system that assesses whether genes have relatively more or less functional genetic variation than expected based on the apparently neutral variation found in the gene. To illustrate the utility of this intolerance score, we show that genes responsible for Mendelian diseases are significantly more intolerant to functional genetic variation than genes that do not cause any known disease, but with striking variation in intolerance among genes causing different classes of genetic disease. We conclude by showing that use of an intolerance ranking system can aid in interpreting personal genomes and identifying pathogenic mutations.
This work uses empirical single nucleotide variant data from the NHLBI Exome Sequencing Project to introduce a genome-wide scoring system that ranks human genes in terms of their intolerance to standing functional genetic variation in the human population. It is often inferred that genes carrying relatively fewer or relatively more common functional variants in healthy individuals may be judged respectively more or less likely to cause certain kinds of disease. We show that this intolerance score correlates remarkably well with genes already known to cause Mendelian diseases (P<10−26). Equally striking, however, are the differences in the relationship between standing genetic variation and disease causing genes for different disease types. Considering disorder classes defined by Goh et al (2007) human disease network, we show a nearly opposite pattern for genes linked to developmental disorders and those linked to immunological disorders, with the former being preferentially caused by genes that do not tolerate functional variation and the latter caused by genes with an excess of common functional variation. We conclude by showing that use of an intolerance ranking system can facilitate interpreting personal genomes and can facilitate identifying high impact mutations through the gene in which they occur.
Multiple genome-wide association studies (GWAS) have been performed in HIV-1 infected individuals, identifying common genetic influences on viral control and disease course. Similarly, common genetic correlates of acquisition of HIV-1 after exposure have been interrogated using GWAS, although in generally small samples. Under the auspices of the International Collaboration for the Genomics of HIV, we have combined the genome-wide single nucleotide polymorphism (SNP) data collected by 25 cohorts, studies, or institutions on HIV-1 infected individuals and compared them to carefully matched population-level data sets (a list of all collaborators appears in Note S1 in Text S1). After imputation using the 1,000 Genomes Project reference panel, we tested approximately 8 million common DNA variants (SNPs and indels) for association with HIV-1 acquisition in 6,334 infected patients and 7,247 population samples of European ancestry. Initial association testing identified the SNP rs4418214, the C allele of which is known to tag the HLA-B*57:01 and B*27:05 alleles, as genome-wide significant (p = 3.6×10−11). However, restricting analysis to individuals with a known date of seroconversion suggested that this association was due to the frailty bias in studies of lethal diseases. Further analyses including testing recessive genetic models, testing for bulk effects of non-genome-wide significant variants, stratifying by sexual or parenteral transmission risk and testing previously reported associations showed no evidence for genetic influence on HIV-1 acquisition (with the exception of CCR5Δ32 homozygosity). Thus, these data suggest that genetic influences on HIV acquisition are either rare or have smaller effects than can be detected by this sample size.
Comparing the frequency differences between common DNA variants in disease-affected cases and in unaffected controls has been successful in uncovering the genetic component of multiple diseases. This approach is most effective when large samples of cases and controls are available. Here we combine information from multiple studies of HIV infected patients, including more than 6,300 HIV+ individuals, with data from 7,200 general population samples of European ancestry to test nearly 8 million common DNA variants for an impact on HIV acquisition. With this large sample we did not observe any single common genetic variant that significantly associated with HIV acquisition. We further tested 22 variants previously identified by smaller studies as influencing HIV acquisition. With the exception of a deletion polymorphism in the CCR5 gene (CCR5Δ32) we found no convincing evidence to support these previous associations. Taken together these data suggest that genetic influences on HIV acquisition are either rare or have smaller effects than can be detected by this sample size.
To evaluate systematically in real clinical settings whether functional genetic variations in drug metabolizing enzymes influence optimized doses, efficacy, and safety of antipsychotic medications.
DNA was collected from 750 patients with chronic schizophrenia treated with five antipsychotic drugs (olanzapine, quetiapine, risperidone, ziprasidone and perphenazine) as part of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study. Doses for each of the medicines were optimized to 1, 2, 3, or 4x units in identically-appearing capsules in a double blind design. We analyzed 25 known functional genetic variants in the major and minor metabolizing enzymes for each medication. These variants were tested for association with optimized dose and other relevant clinical outcomes.
None of the tested variants showed a nominally significant main effect in association with any of the tested phenotypes in European-Americans, African-Americans or all patients. Even after accounting for potential covariates no genetic variant was found to be associated with dosing, efficacy, overall tolerability, or tardive dyskinesia.
There are no strong associations between common functional genetic variants in drug metabolizing enzymes and dosing, safety or efficacy of leading antipsychotics, strongly suggesting merely modest effects on the use of these medicines in most patients in typical clinical settings.
Pharmacogenetics; CYP 450; Drug Metabolizing Enzymes; Antipsychotics; Personalized Medicine
Genetic variation in the IL28B region has been associated with sustained virological response (SVR) rates in chronic hepatitis C (CHC) patients treated with peginterferon-α and ribavirin. We hypothesized that IL28B polymorphism is associated with intrahepatic expression of interferon-stimulated genes (ISGs), known to influence treatment outcome. IL28B genotyping (rs12979860) and whole-genome RNA expression were performed using liver biopsies from 61 North American CHC patients. After correction for multiple testing (false discovery rate < 0.10), 164 transcripts were found to be differentially expressed by IL28B-type. The interferon signaling pathway was the most enriched canonical pathway differentially expressed by IL28B-type (p < 10−5), with most genes showing higher expression in livers of individuals carrying the poor-response IL28B-type. In 25 patients for which treatment response data were available, IL28B-type was associated with SVR (p = 0.0054). ISG expression was also associated with SVR; however, this was not independent of IL28B-type. Analysis of miR-122 expression in liver biopsies showed reduced miR-122 levels associated with poorer treatment outcome, independently of IL28B-type. No association was observed between IL28B-type and levels of liver IL28B or IL28A mRNA expression. IL28B protein sequence variants associated with rs12979860 were therefore investigated in vitro: no differences in ISG induction or inhibition of HCV replication were observed in Huh7.5 cells.
The good response IL28B variant was strongly associated with lower level ISG expression. The results suggest that IL28B genotype may explain the relationship between hepatic ISG expression and HCV treatment outcome, and this is independent of miR-122 expression. IL28B-type was not associated with intrahepatic IL28B mRNA expression in vivo. Further investigation of the precise molecular mechanism(s) by which IL28B genetic variation influences HCV outcomes is warranted.
interferon lambda; hepatitis C virus; gene expression
A single-nucleotide polymorphism (rs2395029) in the HCP5 gene associated with HLA-B*5701 is correlated with lower HIV-1 viral set point. The two allelic forms of coding region were ectopically expressed in TZM-bl cells for an effect on HIV-1 replication. No significant HIV-1 restriction was observed in the cells with infectivity assays throughout HIV-1 life cycle, suggesting that the association of HCP5 variant with viral control is likely due to HLA-B*5701-related effect or other functional variants in the haplotype or both.
Background & Aims
Interferon-alfa (IFN)-related cytopenias are common and may be dose-limiting. We performed a genome wide association study on a well-characterized genotype 1 HCV cohort to identify genetic determinants of peginterferon-α (peg-IFN)-related thrombocytopenia, neutropenia, and leukopenia.
1604/3070 patients in the IDEAL study consented to genetic testing. Trial inclusion criteria included a platelet (Pl) count ≥80 × 109/L and an absolute neutrophil count (ANC) ≥ 1500/mm3. Samples were genotyped using the Illumina Human610-quad BeadChip. The primary analyses focused on the genetic determinants of quantitative change in cell counts (Pl, ANC, lymphocytes, monocytes, eosinophils, and basophils) at week 4 in patients >80% adherent to therapy (n = 1294).
6 SNPs on chromosome 20 were positively associated with Pl reduction (top SNP rs965469, p = 10−10). These tag SNPs are in high linkage disequilibrium with 2 functional variants in the ITPA gene, rs1127354 and rs7270101, that cause ITPase deficiency and protect against ribavirin (RBV)-induced hemolytic anemia (HA). rs1127354 and rs7270101 showed strong independent associations with Pl reduction (p = 10−12, p = 10−7) and entirely explained the genome-wide significant associations. We believe this is an example of an indirect genetic association due to a reactive thrombocytosis to RBV-induced anemia: Hb decline was inversely correlated with Pl reduction (r = −0.28, p = 10−17) and Hb change largely attenuated the association between the ITPA variants and Pl reduction in regression models. No common genetic variants were associated with pegIFN-induced neutropenia or leucopenia.
Two ITPA variants were associated with thrombocytopenia; this was largely explained by a thrombocytotic response to RBV-induced HA attenuating IFN-related thrombocytopenia. No genetic determinants of pegIFN-induced neutropenia were identified.
GWAS; ITPA; Thrombocytopenia; Hepatitis C; Neutropenia; IL28B
A new study focuses attention on multigenic interactions influencing the risk of autism spectrum disorders.
Alternating hemiplegia of childhood (AHC) is a rare, severe neurodevelopmental syndrome characterized by recurrent hemiplegic episodes and distinct neurologic manifestations. AHC is usually a sporadic disorder with unknown etiology. Using exome sequencing of seven patients with AHC, and their unaffected parents, we identified de novo nonsynonymous mutations in ATP1A3 in all seven AHC patients. Subsequent sequence analysis of ATP1A3 in 98 additional patients revealed that 78% of AHC cases have a likely causal ATP1A3 mutation, including one inherited mutation in a familial case of AHC. Remarkably, six ATP1A3 mutations explain the majority of patients, including one observed in 36 patients. Unlike ATP1A3 mutations that cause rapid-onset-dystonia-parkinsonism, AHC-causing mutations revealed consistent reductions in ATPase activity without effects on protein expression. This work identifies de novo ATP1A3 mutations as the primary cause of AHC, and offers insight into disease pathophysiology by expanding the spectrum of phenotypes associated with mutations in this gene.
Amyotrophic lateral sclerosis (ALS) is a late-onset neurodegenerative disorder resulting from motor neuron death. Approximately 10% of cases are familial (FALS), typically with a dominant inheritance mode. Despite numerous advances in recent years1-9, nearly 50% of FALS cases have unknown genetic etiology. Here we show that mutations within the profilin 1 (PFN1) gene can cause FALS. PFN1 is critical for monomeric (G)-actin conversion to filamentous (F)-actin. Exome sequencing of two large ALS families revealed different mutations within the PFN1 gene. Additional sequence analysis identified 4 mutations in 7 out of 274 FALS cases. Cells expressing PFN1 mutants contain ubiquitinated, insoluble aggregates that in many cases contain the ALS-associated protein TDP-43. PFN1 mutants also display decreased bound actin levels and can inhibit axon outgrowth. Furthermore, primary motor neurons expressing mutant PFN1 display smaller growth cones with a reduced F-/G-actin ratio. These observations further document that cytoskeletal pathway alterations contribute to ALS pathogenesis.
Background. A recent genome-wide association study reported a strong association with a single-nucleotide polymorphism (SNP) in the inosine triphosphate (ITPA) gene and hemolytic anemia in patients infected with hepatitis C virus (HCV) receiving pegylated interferon and ribavirin. We investigate these polymorphisms in a cohort of human immunodeficiency virus (HIV)/HCV–coinfected patients.
Methods. DNA was available for 161 patients with validated outcomes. We analyzed the association between the variants and week 4 hemoglobin reduction. Anemia over the course of therapy, ribavirin (RBV) dose reduction, serum RBV level, and rapid virological response (RVR) and sustained virological response (SVR) were also investigated. Using a candidate gene approach, ITPA variants rs1127354 and rs7270101 were tested using the ABI TaqMan kit. Multivariable models were used to identify predictors of anemia.
Results. A significant minority (33%) of patients were predicted to have reduced ITPase activity. The minor allele of each variant was associated with protection against week 4 anemia. In multivariable models only the genetic variants, creatinine, and zidovudine exposure remained significant. ITPase deficiency was not associated with RBV-dose reduction, RVR, or SVR.
Conclusions. This study confirms that polymorphisms in the ITPA gene are associated with protection from RBV-induced anemia in HIV/HCV-coinfected patients but not improved clinical outcomes.
Topiramate is an antiepileptic drug that has marked, treatment-limiting side effects on specific aspects of cognitive performance in both patients and healthy volunteers. As these severe side-effects occur only in certain individuals, identifying genetic or environmental variables that influence cognitive response would be of great utility in determining whether to administer this drug to a patient. We gave an acute 100 mg oral dose of topiramate to 158 healthy volunteers and measured how the drug changed their performance on a diverse battery of cognitive tests. We found a wide range of responses to topiramate and demonstrated that not all tests in the battery were equally affected. There was no correlation between the effect of topiramate and either education level or baseline cognitive performance. Interestingly, there was up to 55-fold variation in the topiramate plasma levels of the participants. Our genome-wide association study (GWAS) of cognitive response did not reveal any genome-wide significant associations; the study was powered to find variants explaining at least 25% of the variation in cognitive response. Combining the results of this GWAS with a retrospective study of cognitive complaints in 290 epilepsy patients who received topiramate as part of their treatment also did not result in a significant association. Our results support the need for additional genetic studies of topiramate that utilize larger sample sizes.
topiramate; cognition; genome-wide association study; genetics; taste change
Partial epilepsies have a substantial heritability. However, the actual genetic causes are largely unknown. In contrast to many other common diseases for which genetic association-studies have successfully revealed common variants associated with disease risk, the role of common variation in partial epilepsies has not yet been explored in a well-powered study. We undertook a genome-wide association-study to identify common variants which influence risk for epilepsy shared amongst partial epilepsy syndromes, in 3445 patients and 6935 controls of European ancestry. We did not identify any genome-wide significant association. A few single nucleotide polymorphisms may warrant further investigation. We exclude common genetic variants with effect sizes above a modest 1.3 odds ratio for a single variant as contributors to genetic susceptibility shared across the partial epilepsies. We show that, at best, common genetic variation can only have a modest role in predisposition to the partial epilepsies when considered across syndromes in Europeans. The genetic architecture of the partial epilepsies is likely to be very complex, reflecting genotypic and phenotypic heterogeneity. Larger meta-analyses are required to identify variants of smaller effect sizes (odds ratio <1.3) or syndrome-specific variants. Further, our results suggest research efforts should also be directed towards identifying the multiple rare variants likely to account for at least part of the heritability of the partial epilepsies. Data emerging from genome-wide association-studies will be valuable during the next serious challenge of interpreting all the genetic variation emerging from whole-genome sequencing studies.
partial epilepsy; genome-wide association; genetics; common variants
The genetic basis of variation in human cognitive abilities is poorly understood. RIMS1 encodes a synapse active‐zone protein with important roles in the maintenance of normal synaptic function: mice lacking this protein have greatly reduced learning ability and memory function.
An established paradigm examining the structural and functional effects of mutations in genes expressed in the eye and the brain was used to study a kindred with an inherited retinal dystrophy due to RIMS1 mutation.
Materials and methods
Neuropsychological tests and high‐resolution MRI brain scanning were undertaken in the kindred. In a population cohort, neuropsychological scores were associated with common variation in RIMS1. Additionally, RIMS1 was sequenced in top‐scoring individuals. Evolution of RIMS1 was assessed, and its expression in developing human brain was studied.
Affected individuals showed significantly enhanced cognitive abilities across a range of domains. Analysis suggests that factors other than RIMS1 mutation were unlikely to explain enhanced cognition. No association with common variation and verbal IQ was found in the population cohort, and no other mutations in RIMS1 were detected in the highest scoring individuals from this cohort. RIMS1 protein is expressed in developing human brain, but RIMS1 does not seem to have been subjected to accelerated evolution in man.
A possible role for RIMS1 in the enhancement of cognitive function at least in this kindred is suggested. Although further work is clearly required to explore these findings before a role for RIMS1 in human cognition can be formally accepted, the findings suggest that genetic mutation may enhance human cognition in some cases.
Single-nucleotide polymorphisms (SNPs) in the IL28B and PNPLA3 gene regions have been associated with hepatic steatosis in genotype 1 (G1) chronic HCV infection but their clinical impacts remain to be determined.
We sought to validate these associations and to explore their impact on treatment response to peginterferon and ribavirin therapy.
A total of 972 G1 HCV-infected Caucasian patients were genotyped for the SNPs rs12979860 (IL28B) and rs2896019 (PNPLA3). Multivariable analysis tested IL28B and PNPLA3 for association with the presence of any steatosis (>0 %); clinically significant steatosis (>5 %); steatosis severity (grade 0–3/4); and the interacting associations of the SNPs and hepatic steatosis to sustained viral response (SVR).
IL28B and PNPLA3 polymorphisms were associated with the presence of any steatosis (rs12979860, p = 1.87 × 10−7; rs2896019, p = 7.56 × 10−4); clinically significant steatosis (rs12979860, p = 1.82 × 10−3; rs2896019, p = 1.27 × 10−4); and steatosis severity (rs12979860, p = 2.05 × 10−8; rs2896019, p = 2.62 × 10−6). Obesity, hypertriglyceridemia, hyperglycemia, liver fibrosis, and liver inflammation were all independently associated with worse steatosis. Hepatic steatosis was associated with lower SVR, and this effect was attenuated by IL28B. PNPLA3 had no independent association with SVR.
IL28B and PNPLA3 are associated with hepatic steatosis prevalence and severity in Caucasians with G1 HCV, suggesting differing potential genetic risk pathways to steatosis. IL28B attenuates the association between steatosis and SVR. Remediable metabolic risk factors remain important, independently of these polymorphisms, and remain key therapeutic goals to achieve better outcomes for patients with HCV-associated hepatic steatosis.
Polymorphism, single-nucleotide, SNP; IL28B protein, human; PNPLA3 protein, human; Adiponutrin, human; Fatty liver; Abdominal obesity metabolic syndrome
We sequenced the genomes of ten unrelated individuals and identified heterozygous stop gain variants in protein-coding genes: we then sequenced their transcriptomes and assessed the expression levels of the stop gain alleles. An ANOVA showed statistically significant differences between their expression levels (p=4×10-16). This difference was almost entirely accounted for by whether the stop gain variant had a second, non-protein-truncating function in or near an alternate transcript: stop gains without alternate functions were generally not found in the cDNA (p=3×10-5). Additionally, stop gain variants in two intronless genes were not expressed, an unexpected outcome given previous studies. In this study, stop gain variants were either well expressed in all individuals or were never expressed. Our finding that stop gain variants were generally expressed only when they had an alternate function suggests that most naturally occurring stop gain variants in protein-coding genes are either not transcribed or have their transcripts destroyed.
Nonsense-mediated decay; whole-genome sequencing; RNA-Seq; premature termination codons
With rapid advances in our knowledge of the human genome and increasing availability of high-throughput investigative technology, genome-wide association (GWA) studies have recently gained marked popularity. As an unbiased approach to identifying genomic regions of importance in complex human disease, the results of such studies have the potential to illuminate novel causal pathways, guide mechanistic research, and aid in prediction of disease risk. The use of a genome-wide approach presents considerable methodological and statistical challenges, and properly conducted studies are essential to avoid false-positive results. A total of 22 GWA studies have been published in pulmonary medicine thus far, implicating several intriguing genomic regions in the determination of pulmonary function measures, onset of asthma, and susceptibility to chronic obstructive pulmonary disease. Many questions remain, however, as most identified genetic variants contribute only nominally to overall disease risk, genetic disease mechanisms remain uncertain, and disease-associated variants are not consistent across studies. Perhaps most fundamentally, the association signals identified have not yet been traced to causal variants. This perspective will review the current state of GWA studies in pulmonary disease. We begin with an introduction to the hypothesis, principles, and limitations of this type of genome-wide approach, highlight key points from available studies, and conclude by addressing future approaches to better understand the genetics of complex pulmonary disease.
genetics; chronic obstructive pulmonary disease; asthma
Brain-derived neurotrophic factor (BDNF) is a neurotrophin which has been shown to regulate cell survival and proliferation, as well as synaptic growth and hippocampal long-term potentiation. A naturally occurring single nucleotide polymorphism in the human BDNF gene (val66met) has been associated with altered intercellular trafficking and regulated secretion of BDNF in met compared to val carriers. Additionally, previous studies have found a relationship between the BDNF val66met genotype and functional activity in the hippocampus during episodic and working memory tasks in healthy young adults. Specifically, studies have found that met carriers exhibit both poorer performance and reduced neural activity within the medial temporal lobe (MTL) when performing episodic memory tasks. However, these studies have not been well replicated and have not considered the role of behavioral differences in the interpretation of neural differences. The current study sought to control for cognitive performance in investigating the role of the BDNF val66met genotype on neural activity associated with episodic memory. Across item and relational memory tests, met carriers exhibited increased MTL activation during both encoding and retrieval stages, compared to non-carriers. The results suggest that met carriers are able to recruit MTL activity to support successful memory processes, and reductions in cognitive performance observed in prior studies are not a ubiquitous effect associated with variants of the BDNF val66met genotype.