An evolutionary perspective on complex neuropsychiatric disease

The forces of evolution-mutation, selection, migration, and genetic drift-shape the genetic architecture of human traits, including the genetic architecture of complex neuropsychiatric illnesses. Studying these illnesses in populations that are diverse in genetic ancestry, historical demography, and cultural history can reveal how evolutionary forces have guided adaptation over time and place. A fundamental truth of shared human biology is that an allele responsible for a disease in anyone, anywhere, reveals a gene critical to the normal biology underlying that condition in everyone, everywhere. Understanding the genetic causes of neuropsychiatric disease in the widest possible range of human populations thus yields the greatest possible range of insight into genes critical to human brain development. In this perspective, we explore some of the relationships between genes, adaptation, and history that can be illuminated by an evolutionary perspective on studies of complex neuropsychiatric disease in diverse populations.

Whole-Exome Sequencing of 21 Families: Candidate Genes for Early-Onset High Myopia

High myopia is the most severe and pathological form of myopia. It occurs when the spherical refractive error exceeds -6.00 spherical diopters (SDs) or the axial length (AL) of the eye is greater than 26 mm. This article focuses on early-onset high myopia, an increasingly common condition that affects children under 10 years of age and can lead to other serious ocular pathologies. Through the genetic analysis of 21 families with early-onset high myopia, this study seeks to contribute to a better understanding of the role of genetics in this disease and to propose candidate genes. Whole-exome sequencing studies with a panel of genes known to be involved in the pathology were performed in families with inconclusive results: 3% of the variants found were classified as pathogenic, 6% were likely pathogenic and the remaining 91% were variants of uncertain significance. Most of the families in this study were found to have alterations in several of the proposed genes. This suggests a polygenic inheritance of the pathology due to the cumulative effect of the alterations. Further studies are needed to validate and confirm the role of these alterations in the development of early-onset high myopia and its polygenic inheritance.

Complex traits and candidate genes: estimation of genetic variance components across multiple genetic architectures

Large-effect loci-those statistically significant loci discovered by genome-wide association studies or linkage mapping-associated with key traits segregate amidst a background of minor, often undetectable, genetic effects in wild and domesticated plants and animals. Accurately attributing mean differences and variance explained to the correct components in the linear mixed model analysis is vital for selecting superior progeny and parents in plant and animal breeding, gene therapy, and medical genetics in humans. Marker-assisted prediction and its successor, genomic prediction, have many advantages for selecting superior individuals and understanding disease risk. However, these two approaches are less often integrated to study complex traits with different genetic architectures. This simulation study demonstrates that the average semivariance can be applied to models incorporating Mendelian, oligogenic, and polygenic terms simultaneously and yields accurate estimates of the variance explained for all relevant variables. Our previous research focused on large-effect loci and polygenic variance separately. This work aims to synthesize and expand the average semivariance framework to various genetic architectures and the corresponding mixed models. This framework independently accounts for the effects of large-effect loci and the polygenic genetic background and is universally applicable to genetics studies in humans, plants, animals, and microbes.

Inheritance of Early and Late Ascochyta Blight Resistance in Wide Crosses of Chickpea

Chickpea (Cicer arietinum) is a globally important food legume but its yield is negatively impacted by the fungal pathogen Ascochyta blight (Ascochyta rabiei) causing necrotic lesions leading to plant death. Past studies have found that Ascochyta resistance is polygenic. It is important to find new resistance genes from the wider genepool of chickpeas. This study reports the inheritance of Ascochyta blight resistance of two wide crosses between the cultivar Gokce and wild chickpea accessions of C. reticulatum and C. echinospermum under field conditions in Southern Turkey. Following inoculation, infection damage was scored weekly for six weeks. The families were genotyped for 60 SNPs mapped to the reference genome for quantitative locus (QTL) mapping of resistance. Family lines showed broad resistance score distributions. A late responding QTL on chromosome 7 was identified in the C. reticulatum family and three early responding QTLs on chromosomes 2, 3, and 6 in the C. echinospermum family. Wild alleles mostly showed reduced disease severity, while heterozygous genotypes were most diseased. Interrogation of 200k bp genomic regions of the reference CDC Frontier genome surrounding QTLs identified nine gene candidates involved in disease resistance and cell wall remodeling. This study identifies new candidate chickpea Ascochyta blight resistance QTLs of breeding potential.

Combining canopy reflectance spectrometry and genome-wide prediction to increase response to selection for powdery mildew resistance in cultivated strawberry

High-throughput phenotyping is an emerging approach in plant science, but thus far only a few applications have been made in horticultural crop breeding. Remote sensing of leaf or canopy spectral reflectance can help breeders rapidly measure traits, increase selection accuracy, and thereby improve response to selection. In the present study, we evaluated the integration of spectral analysis of canopy reflectance and genomic information for the prediction of strawberry (Fragaria × ananassa) powdery mildew disease. Two multi-parental breeding populations of strawberry comprising a total of 340 and 464 pedigree-connected seedlings were evaluated in two separate seasons. A single-trait Bayesian prediction method using 1001 spectral wavebands in the ultraviolet-visible-near infrared region (350-1350 nm wavelength) combined with 8552 single nucleotide polymorphism markers showed up to 2-fold increase in predictive ability over models using markers alone. The integration of high-throughput phenotyping was further validated independently across years/trials with improved response to selection of up to 90%. We also conducted Bayesian multi-trait analysis using the estimated vegetative indices as secondary traits. Three vegetative indices (Datt3, REP_Li, and Vogelmann2) had high genetic correlations (rA) with powdery mildew visual ratings with average rA values of 0.76, 0.71, and 0.71, respectively. Increasing training population sizes by incorporating individuals with only vegetative index information yielded substantial increases in predictive ability. These results strongly indicate the use of vegetative indices as secondary traits for indirect selection. Overall, combining spectrometry and genome-wide prediction improved selection accuracy and response to selection for powdery mildew resistance, demonstrating the power of an integrated phenomics-genomics approach in strawberry breeding.

Evaluation of the Genetic Variance of Alzheimer's Disease Explained by the Disease-Associated Chromosomal Regions

Heritability analysis of complex traits/diseases is commonly performed to obtain illustrative information about the potential contribution of the genetic factors to their phenotypic variances. In this study, we investigated the narrow-sense heritability (h2) of Alzheimer's disease (AD) using genome-wide single-nucleotide polymorphisms (SNPs) data from three independent studies in the linear mixed models framework. Our meta-analyses demonstrated that the estimated h2 values (and their standard errors) of AD in liability scale were 0.280 (0.091), 0.348 (0.113), and 0.389 (0.126) assuming AD prevalence rates of 10%, 20%, or 30% at ages of 65+, 75+, and 85+ years, respectively. We also found that chromosomal regions containing two or more AD-associated SNPs at p < 5E-08 could collectively explain 37% of the additive genetic variance of AD in our samples. AD-associated regions in which at least one SNP had attained p < 5E-08 explained 56% of the additive genetic variance of AD. These regions harbored 3% and 11% of SNPs in our analyses. Also, the chromosomal regions containing two or more and one or more AD-associated SNPs at p < 5E-06 accounted for 72% and 94% of the additive genetic variance of AD, respectively. These regions harbored 27% and 44% of SNPs in our analyses. Our findings showed that the overall contribution of the additive genetic effects to the AD liability was moderate and age-dependent. Also, they supported the importance of focusing on known AD-associated chromosomal regions to investigate the genetic basis of AD, e.g., through haplotype analysis, analysis of heterogeneity, and functional studies.

Patients With High Genome-Wide Polygenic Risk Scores for Coronary Artery Disease May Receive Greater Clinical Benefit From Alirocumab Treatment in the ODYSSEY OUTCOMES Trial

BACKGROUND

Alirocumab, an antibody that blocks PCSK9 (proprotein convertase subtilisin/kexin type 9), was associated with reduced major adverse cardiovascular events (MACE) and death in the ODYSSEY OUTCOMES trial (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab). In this study, higher baseline levels of low-density lipoprotein cholesterol (LDL-C) predicted greater benefit from alirocumab treatment. Recent studies indicate high polygenic risk scores (PRS) for coronary artery disease (CAD) identify individuals at higher risk who derive increased benefit from statins. We performed post hoc analyses to determine whether high PRS for CAD identifies higher-risk individuals, independent of baseline LDL-C and other known risk factors, who might derive greater benefit from alirocumab treatment.

METHODS

ODYSSEY OUTCOMES was a randomized, double-blind, placebo-controlled trial comparing alirocumab or placebo in 18 924 patients with acute coronary syndrome and elevated atherogenic lipoproteins despite optimized statin treatment. The primary endpoint (MACE) comprised death of CAD, nonfatal myocardial infarction, ischemic stroke, or unstable angina requiring hospitalization. A genome-wide PRS for CAD comprising 6 579 025 genetic variants was evaluated in 11 953 patients with available DNA samples. Analysis of MACE risk was performed in placebo-treated patients, whereas treatment benefit analysis was performed in all patients.

RESULTS

The incidence of MACE in the placebo group was related to PRS for CAD: 17.0% for high PRS patients (>90th percentile) and 11.4% for lower PRS patients (≤90th percentile; P<0.001); this PRS relationship was not explained by baseline LDL-C or other established risk factors. Both the absolute and relative reduction of MACE by alirocumab compared with placebo was greater in high versus low PRS patients. There was an absolute reduction by alirocumab in high versus low PRS groups of 6.0% and 1.5%, respectively, and a relative risk reduction by alirocumab of 37% in the high PRS group (hazard ratio, 0.63 [95% CI, 0.46-0.86]; P=0.004) versus a 13% reduction in the low PRS group (hazard ratio, 0.87 [95% CI, 0.78-0.98]; P=0.022; interaction P=0.04).

CONCLUSIONS

A high PRS for CAD is associated with elevated risk for recurrent MACE after acute coronary syndrome and a larger absolute and relative risk reduction with alirocumab treatment, providing an independent tool for risk stratification and precision medicine.

Family Clustering of Autoimmune Vitiligo Results Principally from Polygenic Inheritance of Common Risk Alleles

Vitiligo is an autoimmune disease that results in patches of depigmented skin and hair. Previous genome-wide association studies (GWASs) of vitiligo have identified 50 susceptibility loci. Variants at the associated loci are generally common and have individually small effects on risk. Most vitiligo cases are "simplex," where there is no family history of vitiligo, though occasional family clustering of vitiligo occurs, and some "multiplex" families report numerous close affected relatives. Here, we investigate whether simplex and multiplex vitiligo comprise different disease subtypes with different underlying genetic etiologies. We developed and compared the performance of several different vitiligo polygenic risk scores derived from GWAS data. By using the best-performing risk score, we find increased polygenic burden of risk alleles identified by GWAS in multiplex vitiligo cases relative to simplex cases. We additionally find evidence of polygenic transmission of common, low-effect-size risk alleles within multiplex-vitiligo-affected families. Our findings strongly suggest that family clustering of vitiligo involves a high burden of the same common, low-effect-size variants that are relevant in simplex cases. We furthermore find that a variant within the major histocompatibility complex (MHC) class II region contributes disproportionately more to risk in multiplex vitiligo cases than in simplex cases, supporting a special role for adaptive immune triggering in the etiology of multiplex cases. We suggest that genetic risk scores can be a useful tool in analyzing the genetic architecture of clinical disease subtypes and identifying subjects with unusual etiologies for further investigation.

A robust method to estimate regional polygenic correlation under misspecified linkage disequilibrium structure

Complex traits can share a substantial proportion of their polygenic heritability. However, genome-wide polygenic correlations between pairs of traits can mask heterogeneity in their shared polygenic effects across loci. We propose a novel method (weighted maximum likelihood-regional polygenic correlation [RPC]) to evaluate polygenic correlation between two complex traits in small genomic regions using summary association statistics. Our method tests for evidence that the polygenic effect at a given region affects two traits concurrently. We show through simulations that our method is well calibrated, powerful, and more robust to misspecification of linkage disequilibrium than other methods under a polygenic model. As small genomic regions are more likely to harbor specific genetic effects, our method is ideal to identify heterogeneity in shared polygenic correlation across regions. We illustrate the usefulness of our method by addressing two questions related to cardiometabolic traits. First, we explored how RPC can inform on the strong epidemiological association between high-density lipoprotein cholesterol and coronary artery disease (CAD), suggesting a key role for triglycerides metabolism. Second, we investigated the potential role of PPARγ activators in the prevention of CAD. Our results provide a compelling argument that shared heritability between complex traits is highly heterogeneous across loci.

[Genetic heterogeneity and complexity of congenital heart defects]

Congenital heart defects are the most common birth defects, they account for approximately one third of all cases. They are clinically heterogeneous, vary widely in severity, treatability and prognosis and may occur as part of multiple developmental disorders, such as chromosome aberrations, microdeletion syndromes and monogenic diseases, or as isolated defects. Syndromic forms account for 25-40%, isolated forms for 60-75% of all cases. With conventional cytogenetic and next-generation molecular genetic methods, numerous genetic alterations have been identified in evolutionarily highly conserved genes of transcriptional regulators, signaling molecules and structural proteins, which are critical to normal cardiogenesis, mostly in cases with syndromic congenital heart defects. On the other hand, the genetic cause can be detected only in around 11% of isolated heart defects. The survival rate and life quality of patients with congenital heart defects have improved significantly in the last decades thanks to the remarkable development of prenatal, postnatal diagnostics as well as of heart and thoracic surgery of cardiovascular diseases. Since the number of patients, living into adulthood and reproductive age, is constantly increasing, the better understanding of the genetics of congenital heart defects may be crucial for the diagnosis, prognosis and positive family planning of patients. Orv Hetil. 2018; 159(17): 661-670.

Penetrance of Polygenic Obesity Susceptibility Loci across the Body Mass Index Distribution

A growing number of single-nucleotide polymorphisms (SNPs) have been associated with body mass index (BMI) and obesity, but whether the effects of these obesity-susceptibility loci are uniform across the BMI distribution remains unclear. We studied the effects of 37 BMI-associated SNPs in 75,230 adults of European ancestry across BMI percentiles by using conditional quantile regression (CQR) and meta-regression (MR) models. The effects of nine SNPs (24%)-rs1421085 (FTO; p = 8.69 × 10-15), rs6235 (PCSK1; p = 7.11 × 10-6), rs7903146 (TCF7L2; p = 9.60 × 10-6), rs11873305 (MC4R; p = 5.08 × 10-5), rs12617233 (FANCL; p = 5.30 × 10-5), rs11672660 (GIPR; p = 1.64 × 10-4), rs997295 (MAP2K5; p = 3.25 × 10-4), rs6499653 (FTO; p = 6.23 × 10-4), and rs3824755 (NT5C2; p = 7.90 × 10-4)-increased significantly across the sample BMI distribution. We showed that such increases stemmed from unadjusted gene interactions that enhanced the effects of SNPs in persons with a high BMI. When 125 height-associated SNPs were analyzed for comparison, only one (<1%), rs6219 (IGF1, p = 1.80 × 10-4), showed effects that varied significantly across height percentiles. Cumulative gene scores of these SNPs (GS-BMI and GS-height) showed that only GS-BMI had effects that increased significantly across the sample distribution (BMI: p = 7.03 × 10-37; height: p = 0.499). Overall, these findings underscore the importance of gene-gene and gene-environment interactions in shaping the genetic architecture of BMI and advance a method for detecting such interactions by using only the sample outcome distribution.

Current Status of Early Blight Resistance in Tomato: An Update

Early blight (EB) is one of the dreadful diseases of tomato caused by several species of Alternaria including Alternaria linariae (which includes A. solani and A. tomatophila), as well as A. alternata. In some instances, annual economic yield losses due to EB have been estimated at 79%. Alternaria are known only to reproduce asexually, but a highly-virulent isolate has the potential to overcome existing resistance genes. Currently, cultural practices and fungicide applications are employed for the management of EB due to the lack of strong resistant cultivars. Resistance sources have been identified in wild species of tomato; some breeding lines and cultivars with moderate resistance have been developed through conventional breeding methods. Polygenic inheritance of EB resistance, insufficient resistance in cultivated species and the association of EB resistance with undesirable horticultural traits have thwarted the effective breeding of EB resistance in tomato. Several quantitative trait loci (QTL) conferring EB resistance have been detected in the populations derived from different wild species including Solanum habrochaites, Solanum arcanum and S. pimpinellifolium, but none of them could be used in EB resistance breeding due to low individual QTL effects. Pyramiding of those QTLs would provide strong resistance. More research is needed to identify additional sources of useful resistance, to incorporate resistant QTLs into breeding lines through marker-assisted selection (MAS) and to develop resistant cultivars with desirable horticultural traits including high yielding potential and early maturity. This paper will review the current understanding of causal agents of EB of tomato, resistance genetics and breeding, problems associated with breeding and future prospects.

A comprehensive analysis of rare genetic variation in amyotrophic lateral sclerosis in the UK

Amyotrophic lateral sclerosis is a progressive neurodegenerative disease of motor neurons. About 25 genes have been verified as relevant to the disease process, with rare and common variation implicated. We used next generation sequencing and repeat sizing to comprehensively assay genetic variation in a panel of known amyotrophic lateral sclerosis genes in 1126 patient samples and 613 controls. About 10% of patients were predicted to carry a pathological expansion of the C9orf72 gene. We found an increased burden of rare variants in patients within the untranslated regions of known disease-causing genes, driven by SOD1, TARDBP, FUS, VCP, OPTN and UBQLN2. We found 11 patients (1%) carried more than one pathogenic variant (P = 0.001) consistent with an oligogenic basis of amyotrophic lateral sclerosis. These findings show that the genetic architecture of amyotrophic lateral sclerosis is complex and that variation in the regulatory regions of associated genes may be important in disease pathogenesis.

Rare Variants in Neurodegeneration Associated Genes Revealed by Targeted Panel Sequencing in a German ALS Cohort

Amyotrophic lateral sclerosis (ALS) is a progressive fatal multisystemic neurodegenerative disorder caused by preferential degeneration of upper and lower motor neurons. To further delineate the genetic architecture of the disease, we used comprehensive panel sequencing in a cohort of 80 German ALS patients. The panel covered 39 confirmed ALS genes and candidate genes, as well as 238 genes associated with other entities of the neurodegenerative disease spectrum. In addition, we performed repeat length analysis for C9orf72. Our aim was to (1) identify potentially disease-causing variants, to (2) assess a proposed model of polygenic inheritance in ALS and to (3) connect ALS with other neurodegenerative entities. We identified 79 rare potentially pathogenic variants in 27 ALS associated genes in familial and sporadic cases. Five patients had pathogenic C9orf72 repeat expansions, a further four patients harbored intermediate length repeat expansions. Our findings demonstrate that a genetic background of the disease can actually be found in a large proportion of seemingly sporadic cases and that it is not limited to putative most frequently affected genes such as C9orf72 or SOD1. Assessing the polygenic nature of ALS, we identified 15 patients carrying at least two rare potentially pathogenic variants in ALS associated genes including pathogenic or intermediate C9orf72 repeat expansions. Multiple variants might influence severity or duration of disease or could account for intrafamilial phenotypic variability or reduced penetrance. However, we could not observe a correlation with age of onset in this study. We further detected potentially pathogenic variants in other neurodegeneration associated genes in 12 patients, supporting the hypothesis of common pathways in neurodegenerative diseases and linking ALS to other entities of the neurodegenerative spectrum. Most interestingly we found variants in GBE1 and SPG7 which might represent differential diagnoses. Based on our findings, we recommend two-staged genetic testing for ALS in Germany in patients with familial and sporadic ALS, comprising C9orf72 repeat analysis followed by comprehensive panel sequencing including differential diagnoses that impair motor neuron function to meet the complexity of ALS genetics.

Mutation analyses in pedigrees and sporadic cases of ethnic Han Chinese Kallmann syndrome patients

Kallmann syndrome, a form of idiopathic hypogonadotropic hypogonadism, is characterized by developmental abnormalities of the reproductive system and abnormal olfaction. Despite association of certain genes with idiopathic hypogonadotropic hypogonadism, the genetic inheritance and expression are complex and incompletely known. In the present study, seven Kallmann syndrome pedigrees in an ethnic Han Chinese population were screened for genetic mutations. The exons and intron-exon boundaries of 19 idiopathic hypogonadotropic hypogonadism (idiopathic hypogonadotropic hypogonadism)-related genes in seven Chinese Kallmann syndrome pedigrees were sequenced. Detected mutations were also tested in 70 sporadic Kallmann syndrome cases and 200 Chinese healthy controls. In pedigrees 1, 2, and 7, the secondary sex characteristics were poorly developed and the patients' sense of smell was severely or completely lost. We detected a genetic mutation in five of the seven pedigrees: homozygous KAL1 p.R191ter (pedigree 1); homozygous KAL1 p.C13ter (pedigree 2; a novel mutation); heterozygous FGFR1 p.R250W (pedigree 3); and homozygous PROKR2 p.Y113H (pedigrees 4 and 5). No genetic change of the assayed genes was detected in pedigrees 6 and 7. Among the 70 sporadic cases, we detected one homozygous and one heterozygous PROKR2 p.Y113H mutation. This mutation was also detected heterozygously in 2/200 normal controls and its pathogenicity is likely questionable. The genetics and genotype-phenotype relationships in Kallmann syndrome are complicated. Classical monogenic inheritance does not explain the full range of genetic inheritance of Kallmann syndrome patients. Because of stochastic nature of genetic mutations, exome analyses of Kallmann syndrome patients may provide novel insights.