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Whole-genome sequencing of monozygotic twins, along with their parents, spouses and children, identifies postzygotic mutations present in the somatic tissue of one twin, but not the other, and characterizes differences in the number and timing of these mutations.

Genome-wide association analyses of migraine and its subtypes identify new susceptibility loci, including rare variants with large effects implicating PRRT2, SCN11A and KCNK5.

Diagnosis and classification of peripheral neuropathy (PN) is facilitated by nerve conduction (NC) studies. Here, Bjornsdottir et al. find a low-frequency PRPH splice-donor variant that associates with NC amplitude and neurological assessment of recalled PRPH variant carriers reveals increased risk of a mild sensory-negative PN.

In this paper gene expression is treated as a quantitative trait in both blood and adipose tissue, and associations between specific genetic loci and body mass index are identified using a molecular network approach.

Analysis of long-read sequencing data from 3,622 Icelanders identifies a set of high-confidence structural variants and provides insights into their effect on human traits and diseases.

Whole-genome sequencing of 78 Icelandic parent–offspring trios is used to study the de novo mutation rate at the genome-wide level; the rate is shown to increase by about two mutations a year as a function of the increasing age of the father at conception, highlighting the importance of father’s age on the risk of diseases such as autism and schizophrenia.

Bjarni Halldorsson, Kari Stefansson and colleagues analyze genomic data from 15,219 Icelanders to identify non-repetitive sequences that are missing from the reference genome. They describe 3,791 breakpoint-resolved sequence variants and find overlap with GWAS markers as well as the presence of a proportion of these variants in the chimpanzee genome.

Patrick Sulem, Hannes Helgason and colleagues identify homozygous and compound heterozygous loss-of-function variants of minor allele frequency <2% in 7.7% of the genotyped Icelandic population. Under transmission of some of these variants from heterozygous parents provides evidence that they are actually deleterious.

Ingileif Jonsdottir, Kari Stefansson and colleagues show that variants in the HLA class II region contribute to tuberculosis risk in populations of European ancestry. They propose that the associated variants influence disease risk by altering expression of HLA class II molecules presenting protective M. tuberculosis antigens to T cells.

Bjarni Halldorsson, Kari Stefansson and colleagues use SNP array and whole-genome sequencing data to estimate the meiotic gene conversion rate (G) in humans. They find that G for SNPs is 7.0 conversions/Mb per generation, is 2.17 greater in mothers than in fathers, and increases with maternal age.

Analysis of whole-genome sequence data of Icelandic individuals has revealed a rare nonsense mutation within the LGR4 gene that is strongly associated with, among other things, low bone mineral density, late onset of menarche, and increased risk of biliary tract cancer.

The effect of sequence variants on phenotypes may depend on parental origin. Here, a method is developed that takes parental origin — the impact of which, to date, has largely been ignored — into account in genome-wide association studies. For 38,167 Icelanders genotyped, the parental origin of most alleles is determined; furthermore, a number of variants are found that show associations specific to parental origin, including three with type 2 diabetes.

Using a combination of whole-genome sequencing, haplotype sharing and the genealogies of the Icelandic population, Thorunn Rafnar, Kari Stefansson and colleagues identified a rare coding mutation in the gene of a BRCA1-interacting factor, BRIP1, that confers a high relative risk of ovarian cancer.

Solveig Gretarsdottir, Kari Stefansson and colleagues report a genome-wide association study for abdominal aortic aneurysm. They identified a variant located within the DAB2IP gene on 9q33 associated with risk of developing abdominal aortic aneurysm.

While the consequences of homozygous loss of function variants have been studied, the effect of missense variants is less understood. Here, the authors identify pathogenic genotypes through an observed deficit of homozygous carriers of missense variants in a population, elucidating previously unexplained recessive disease and miscarriage.

Here, human genome-wide single-nucleotide polymorphism (SNP) data from more than 15,000 parent–offspring pairs have been used to construct the first recombination maps that are based on directly observed recombination events. The data reveal interesting differences between the sexes: for instance, in males recombination tends to shuffle exons, whereas in females it generates new combinations of nearby genes. Comparison of these maps with others also reveals population differences.

Creatine kinase (CK) and lactate dehydrogenase (LDH) are biomarkers of tissue damages including myopathy and myocardial infarction. Here, Patrick Sulem and colleagues perform a genome-wide association study to identify common and rare genetic variants that associates with serum CK or LDH levels.

Whole-genome sequencing identifies a rare missense variant in IKBKB associated with high risk of cutaneous and systemic lupus erythematosus among people with African ancestry.

Graphtyper is a fast and scalable method for variant genotyping that aligns short-read sequence data to a pangenome. Graphtyper was able to accurately genotype ∼90 million sequence variants in the whole genomes of ∼28,000 Icelanders, including those in six HLA genes.

Intellectual disability (ID) is characterized by an intelligence quotient of below 70 and impaired adaptive skills. Here, analyzing whole genome sequences from 31,463 Icelanders, Walters et al. identify variants in MAP1B associated with ID and extensive brain-wide white matter deficits.

Mutations in genes encoding NAPDH oxidase subunits are known to be causative for the primary immunodeficiency chronic granulomatous disease (CGD). Here, the authors identify CYBC1 mutations in patients with CGD and show that CYBC1 is important for formation of the NADPH complex and respiratory burst.

Patrick Sulem and colleagues report a genome-wide association study of age at menarche, finding and replicating an association with LIN28B. The authors test a number of variants previously associated with height and BMI and find that five loci previously associated with BMI are also associated with age at menarche.

Analysis of 1,007 sibling pairs from 251 families identifies 878 de novo mutations shared by siblings at 448 sites. Recurrence probability based on parental somatic mosaicism, sibling sharing, parent of origin, mutation type and genomic position can range from 0.011% to 28.5%.

The genetics of schizophrenia and other mental disorders are complex and poorly understood, and made even harder to study due to reduced reproduction resulting in negative selection pressure on risk alleles. Two independent large-scale genome wide studies of thousands of patients and controls by two international consortia confirm a previously identified locus, but also reveal novel associations. In this study, de novo (spontaneous) copy number variants are reported on chromosomes 1 and 15.

Immunoglobulin G (IgG) is the main isotype of antibody in human blood. Here the authors describe 14 genetic variants that affect IgG levels in blood. The data provide new insight into the regulation of humoral immunity that could be useful in the development of antibody-based therapeutics.

Whole-genome sequencing data of 14,688 Icelanders, including 1,548 parent–offspring trios, show how the age and sex of parents affect the rate and spectrum of de novo mutations.

The concentration of SARS-CoV-2 changes during an individual’s infection, and mutations accumulate as viruses are transmitted between people. Here, the authors use data from Iceland to demonstrate how this information can be exploited at the population-level to determine the phase of the epidemic.

Hilma Holm et al. report a rare missense variant MYH6 that is associated with a high risk of sick sinus syndrome in Icelanders. This heart condition is found most often in elderly people and is the most frequent reason a heart pacemaker is implanted.

Kari Stefansson and colleagues report discovery of 13 variants with large effects on non-HDL cholesterol, LDL cholesterol, HDL cholesterol or triglyceride lipid fractions. They further show that, among these lipid fractions, the non-HDL cholesterol genetic risk score associates most strongly with coronary disease and confers risk beyond that of LDL cholesterol and that, after accounting for non-HDL cholesterol, neither HDL cholesterol nor triglyceride genetic risk scores associate with coronary disease.

Ingileif Jonsdottir, Björn Nilsson, Kari Stefansson and colleagues perform a genome-wide association study for immunoglobulin levels in Icelandic and Swedish cohorts. They find 38 new variants associated with IgA, IgG, IgM or composite immunoglobulin traits and identify candidate genes underlying the regulation of immunoglobulin levels.

Hilma Holm and colleagues report genome-wide association studies to electrocardiographic measures of heart rate, PR interval, QRS duration and QT interval.

A GWAS in Iceland reveals that variants in inner nuclear membrane proteins are associated with nuclear morphology of granulocytes and band neutrophil fraction.

Erna Ivarsdottir et al. report a genome-wide association meta-analysis for age-related hearing loss in the Icelandic and UK populations. They identify 21 novel variants, 13 of which are rare, and reveal a genetic correlation between age-related hearing loss and tinnitus.

Gudjon Oskarsson et al. report a genome-wide association study of hemoglobin concentration in more than 680,000 individuals from Iceland and the UK. They identify six novel rare coding variants at the ACO1 locus that associate with either increased or decreased hemoglobin concentration, two of which have large and opposite effects.

Aimee Deaton et al. identify a rare missense variant in the bile acid receptor gene NR1H4, which is associated with lower levels of total cholesterol in the Icelandic population. Hepatocytes expressing the missense variant showed altered expression of a small number of genes, with enrichment in lipid-related pathways.

Simon Stacey, Kari Stefansson and colleagues show that a germline variant in the TP53 polyadenylation signal is associated with increased risk of basal cell carcinoma and other solid tumors.

Kari Stefansson and colleagues performed a genome-wide association study for severe hand osteoarthritis and found associated variants within the ALDH1A2 gene and at 1p31.

Julius Gudmundsson and colleagues report a genome-wide association study for circulating levels of thyroid-stimulating hormone in 27,758 individuals not known to have thyroid cancer. They follow with thyroid cancer association analyses and identify common variants at three loci newly associated with susceptibility to thyroid cancer.

Simon Stacey and colleagues report results of a genome-wide association study for cutaneous basal cell carcinoma. They identify two loci, at 1p36 and 1q42, associated with BCC risk, and show that neither is associated with melanoma or pigmentation traits.

Kari Stefansson, Unnur Styrkarsdottir and colleagues identify rare genotypes in COMP and CHADL associated with high risk of total hip replacement due to osteoarthritis. The high odds ratios associated with these rare risk genotypes suggest that they may represent Mendelian forms of osteoarthritis.