Population-based and family-based designs to analyze rare variants in complex diseases

Hirschsprung disease (HSCR) is the leading cause of neonatal functional intestinal obstruction. It is a rare congenital disease with an incidence of one in 3,500–5,000 live births. HSCR is characterized by the absence of enteric ganglia in the distal colon, plausibly due to genetic defects perturbing the normal migration, proliferation, differentiation, and/or survival of the enteric neural crest cells as well as impaired interaction with the enteric progenitor cell niche. Early linkage analyses in Mendelian and syndromic forms of HSCR uncovered variants with large effects in major HSCR genes including RET, EDNRB, and their interacting partners in the same biological pathways. With the advances in genome-wide genotyping and next-generation sequencing technologies, there has been a remarkable progress in understanding of the genetic basis of HSCR in the past few years, with common and rare variants with small to moderate effects being uncovered. The discovery of new HSCR genes such as neuregulin and BACE2 as well as the deeper understanding of the roles and mechanisms of known HSCR genes provided solid evidence that many HSCR cases are in the form of complex polygenic/oligogenic disorder where rare variants act in the sensitized background of HSCR-associated common variants. This review summarizes the roadmap of genetic discoveries of HSCR from the earlier family-based linkage analyses to the recent population-based genome-wide analyses coupled with functional genomics, and how these discoveries facilitated our understanding of the genetic architecture of this complex disease and provide the foundation of clinical translation for precision and stratified medicine.

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Identifying the phenotypic effect of rare variants by including between-pedigree coancestry in variance components linkage analysis

10.1101/215863 ◽

2017 ◽

Author(s):

J.E. Hicks ◽

M. A. Province

Keyword(s):

Linkage Analysis ◽

Variance Components ◽

Rare Variants ◽

Simulated Data ◽

Population Based ◽

Pedigree Information ◽

Phenotypic Effect ◽

Sequencing Technologies ◽

Variance Components Analysis ◽

Family Based

AbstractThe contribution of rare variants to disease burden has become an important focus in genetic epidemiology. These effects are difficult to detect in population-based datasets, and as a result, interest in family-based study designs has resurfaced. Linkage analysis tools will need to be updated to accommodate the scale of data generated by modern genotyping and sequencing technologies.In conventional linkage analysis individuals in different pedigrees are assumed to be independent of each other. However, cryptic relatedness is often present in populations and haplotypes that harbor rare variants may be shared between pedigrees as well as within them.With millions of polymorphisms, Identity-by-descent (IBD) states across the genome can now be inferred without use of pedigree information. This is done by identifying long runs of identical-by-state genotypes which are unlikely to arise without IBD. Previously, IBD had to be estimated in pedigrees from recombination events in a sparse set of markers.We present a method for variance-components linkage that can incorporate large number of markers and allows for between-pedigree relatedness. We replace the IBD matrix generated from pedigree-based analysis with one generated from a genotype-based method. All pedigrees in a dataset are considered jointly, allowing between-pedigree IBD to be included in the model.In simulated data, we show that power is increased in the scenario when there is a haplotype shared IBD between members of different pedigrees. If there is no between-pedigree IBD, the analysis reduces to conventional variance-components analysis. By determining IBD states by long runs of dense IBS genotypes, linkage signals can be determined from their physical position, allowing more precise localization.

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Faculty Opinions recommendation of Family-based association test using both common and rare variants and accounting for directions of effects for sequencing data.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.718882382.793500875 ◽

2014 ◽

Author(s):

Melanie Bahlo

Keyword(s):

Rare Variants ◽

Association Test ◽

Sequencing Data ◽

Family Based

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Case–Parent Trio Studies in Cleft Lip and Palate

Global Medical Genetics ◽

10.1055/s-0040-1722097 ◽

2020 ◽

Vol 07 (03) ◽

pp. 075-079

Author(s):

Mahamad Irfanulla Khan ◽

Prashanth CS

Keyword(s):

Genetic Variants ◽

Cleft Lip ◽

Cleft Lip And Palate ◽

Association Studies ◽

Geographical Location ◽

Genetic Association Studies ◽

Population Based ◽

Genome Wide Association Studies ◽

Family Based ◽

Study Designs

AbstractCleft lip with or without cleft palate (CL/P) is one of the most common congenital malformations in humans involving various genetic and environmental risk factors. The prevalence of CL/P varies according to geographical location, ethnicity, race, gender, and socioeconomic status, affecting approximately 1 in 800 live births worldwide. Genetic studies aim to understand the mechanisms contributory to a phenotype by measuring the association between genetic variants and also between genetic variants and phenotype population. Genome-wide association studies are standard tools used to discover genetic loci related to a trait of interest. Genetic association studies are generally divided into two main design types: population-based studies and family-based studies. The epidemiological population-based studies comprise unrelated individuals that directly compare the frequency of genetic variants between (usually independent) cases and controls. The alternative to population-based studies (case–control designs) includes various family-based study designs that comprise related individuals. An example of such a study is a case–parent trio design study, which is commonly employed in genetics to identify the variants underlying complex human disease where transmission of alleles from parents to offspring is studied. This article describes the fundamentals of case–parent trio study, trio design and its significances, statistical methods, and limitations of the trio studies.

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Identification of sixteen novel candidate genes for late onset Parkinson’s disease

Molecular Neurodegeneration ◽

10.1186/s13024-021-00455-2 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Alessandro Gialluisi ◽

Mafalda Giovanna Reccia ◽

Nicola Modugno ◽

Teresa Nutile ◽

Alessia Lombardi ◽

...

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Candidate Genes ◽

Rare Variants ◽

Late Onset ◽

High Specificity ◽

Diagnostic Tools ◽

Multi Stage ◽

Whole Exome ◽

Family Based

Abstract Background Parkinson’s disease (PD) is a neurodegenerative movement disorder affecting 1–5% of the general population for which neither effective cure nor early diagnostic tools are available that could tackle the pathology in the early phase. Here we report a multi-stage procedure to identify candidate genes likely involved in the etiopathogenesis of PD. Methods The study includes a discovery stage based on the analysis of whole exome data from 26 dominant late onset PD families, a validation analysis performed on 1542 independent PD patients and 706 controls from different cohorts and the assessment of polygenic variants load in the Italian cohort (394 unrelated patients and 203 controls). Results Family-based approach identified 28 disrupting variants in 26 candidate genes for PD including PARK2, PINK1, DJ-1(PARK7), LRRK2, HTRA2, FBXO7, EIF4G1, DNAJC6, DNAJC13, SNCAIP, AIMP2, CHMP1A, GIPC1, HMOX2, HSPA8, IMMT, KIF21B, KIF24, MAN2C1, RHOT2, SLC25A39, SPTBN1, TMEM175, TOMM22, TVP23A and ZSCAN21. Sixteen of them have not been associated to PD before, were expressed in mesencephalon and were involved in pathways potentially deregulated in PD. Mutation analysis in independent cohorts disclosed a significant excess of highly deleterious variants in cases (p = 0.0001), supporting their role in PD. Moreover, we demonstrated that the co-inheritance of multiple rare variants (≥ 2) in the 26 genes may predict PD occurrence in about 20% of patients, both familial and sporadic cases, with high specificity (> 93%; p = 4.4 × 10− 5). Moreover, our data highlight the fact that the genetic landmarks of late onset PD does not systematically differ between sporadic and familial forms, especially in the case of small nuclear families and underline the importance of rare variants in the genetics of sporadic PD. Furthermore, patients carrying multiple rare variants showed higher risk of manifesting dyskinesia induced by levodopa treatment. Conclusions Besides confirming the extreme genetic heterogeneity of PD, these data provide novel insights into the genetic of the disease and may be relevant for its prediction, diagnosis and treatment.

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Characterisation of protein-truncating and missense variants in PALB2 in 15 768 women from Malaysia and Singapore

Journal of Medical Genetics ◽

10.1136/jmedgenet-2020-107471 ◽

2021 ◽

pp. jmedgenet-2020-107471

Author(s):

Pei Sze Ng ◽

Rick ACM Boonen ◽

Eldarina Wijaya ◽

Chan Eng Chong ◽

Milan Sharma ◽

...

Keyword(s):

Breast Cancer ◽

Rare Variants ◽

Embryonic Stem ◽

Mouse Embryonic Stem Cell ◽

Population Based ◽

Breast Cancer Patients ◽

Dna Double Strand Breaks ◽

Functional Impact ◽

Missense Variants ◽

Increased Risk

BackgroundRare protein-truncating variants (PTVs) in partner and localiser of BRCA2 (PALB2) confer increased risk to breast cancer, but relatively few studies have reported the prevalence in South-East Asian populations. Here, we describe the prevalence of rare variants in PALB2 in a population-based study of 7840 breast cancer cases and 7928 healthy Chinese, Malay and Indian women from Malaysia and Singapore, and describe the functional impact of germline missense variants identified in this population.MethodsMutation testing was performed on germline DNA (n=15 768) using targeted sequencing panels. The functional impact of missense variants was tested in mouse embryonic stem cell based functional assays.ResultsPTVs in PALB2 were found in 0.73% of breast cancer patients and 0.14% of healthy individuals (OR=5.44; 95% CI 2.85 to 10.39, p<0.0001). In contrast, rare missense variants in PALB2 were not associated with increased risk of breast cancer. Whereas PTVs were associated with later stage of presentation and higher-grade tumours, no significant association was observed with missense variants in PALB2. However, two novel rare missense variants (p.L1027R and p.G1043V) produced unstable proteins and resulted in a decrease in homologous recombination-mediated repair of DNA double-strand breaks.ConclusionDespite genetic and lifestyle differences between Asian and other populations, the population prevalence of PALB2 PTVs and associated relative risk of breast cancer, are similar to those reported in European populations.

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Testing rare variants for hypertension using family-based tests with different weighting schemes

BMC Proceedings ◽

10.1186/s12919-016-0036-7 ◽

2016 ◽

Vol 10 (S7) ◽

Cited By ~ 2

Author(s):

Xuexia Wang ◽

Xingwang Zhao ◽

Jin Zhou

Keyword(s):

Rare Variants ◽

Weighting Schemes ◽

Family Based

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A Systematic Review on Extreme Phenotype Strategies to Search for Rare Variants in Genetic Studies of Complex Disorders

10.20944/preprints202007.0583.v1 ◽

2020 ◽

Author(s):

Sana Amanat ◽

Teresa Requena ◽

Jose Antonio Lopez-Escamez

Keyword(s):

Systematic Review ◽

Candidate Genes ◽

Rare Variants ◽

De Novo ◽

Complex Diseases ◽

De Novo Mutations ◽

Genetic Studies ◽

Complex Disorders ◽

Extreme Phenotype ◽

Age Related

Exome sequencing has been commonly used in rare diseases by selecting multiplex families or singletons with an extreme phenotype (EP) to search for rare variants in coding regions. The EP strategy covers both extreme ends of a disease spectrum and it has been also used to investigate the contribution of rare variants to heritability in complex clinical traits. We have conducted a systematic review to find evidence supporting the use of EP strategies to search for rare variants in genetic studies of complex diseases, to highlight the contribution of rare variation to the genetic structure of multiallelic conditions. After performing the quality assessment of the retrieved records, we selected 19 genetic studies considering EP to demonstrate genetic association. All the studies successfully identified several rare variants, de novo mutations and many novel candidate genes were also identified by selecting an EP. There is enough evidence to support that the EP approach in patients with an early onset of the disease can contribute to the identification of rare variants in candidate genes or pathways involved in complex diseases. EP patients may contribute to a better understanding of the underlying genetic architecture of common heterogeneous disorders such as tinnitus or age-related hearing loss.

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Abstract 12: Heritability of Ischemic Stroke and its Subtypes

Stroke ◽

10.1161/str.43.suppl_1.a12 ◽

2012 ◽

Vol 43 (suppl_1) ◽

Author(s):

Andrew E Bluher ◽

Michael A Nalls ◽

John W Cole ◽

Pankaj Sharma ◽

James F Meschia ◽

...

Keyword(s):

Ischemic Stroke ◽

Fixed Effects ◽

Rare Variants ◽

Phenotypic Variability ◽

Fixed Effects Model ◽

Stroke Subtype ◽

Genome Wide ◽

Weighted Means ◽

Family Based ◽

And Gender

Background and Purpose: Family-based methods for estimating heritability cannot discriminate between shared genetic and shared environmental exposures. Recently, methods have been developed for estimating heritability in population samples using genome-wide SNPs. We used the approach developed by Visscher and colleagues to estimate the heritability of ischemic stroke in Caucasian subjects. In addition to evaluating the overall heritability of ischemic stroke, we assessed whether stroke heritability varies by age, gender, and stroke subtype. Methods: Using publicly available software (GCTA and PLINK), we estimated ischemic stroke heritability stratified by age and gender using genome-wide association (GWA) data from three Caucasian ischemic stroke studies: Ischemic Stroke Genetics Study (ISGS), Bio-Repository of DNA in Stroke (BRAINS), and Genetics of Early-Onset Stroke (GEOS). Weighted means of site-specific heritability point estimates were combined according to a standard fixed effects model. Results: Conclusions: A SNP-based approach may be useful in discerning differences in ischemic stroke heritability between different cohorts and subtypes. Overall, our analysis estimated ischemic stroke heritability to be 31% (SE = 7%), with a suggestion of higher heritability for younger cases. Small vessel stroke showed the highest heritability (58 ± 19%), with cardioembolic showing the lowest heritability (16 ± 14%). It should be emphasized that heritability estimates are population-specific and that the method used only reflects the heritability captured by common SNP variants measured in GWA studies, and not phenotypic variability explained by rare variants.

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