HERC2 rs12913832 modulates human pigmentation by attenuating chromatin-loop formation between a long-range enhancer and the OCA2 promoter

Case Report: Genetic analysis of oculocutaneous albinism type 2 caused by a new mutation in the OCA2

Oculocutaneous albinism (OCA) is a condition inherited in an autosomal recessive manner, leading to reduced pigmentation in the skin, hair, and eyes. Oculocutaneous albinism type 2 (OCA2) is one of the most common forms of OCA, caused by OCA2 mutations. This case report presents a newborn with suspected OCA. Postnatal examination revealed white skin, golden-colored hair, and reduced visibility of the retinal pigmented epithelium on fundus photography. Genomic DNA was extracted from the peripheral blood of the patient and her parents. Whole Exome Sequencing (WES) was conducted using chip capture-based high-throughput sequencing technology to analyze genomic DNA from the proband and her parents. Genetic variants of his parents were identified using sanger sequencing. A mutation in the OCA2 was identified: NM_000275.2: c.863_886delTGAGCAGGACCTTTGAGGTGA (p.Met288_Leu295del). Subsequently genetic analyses were conducted. This mutation was recognized as a potential disease-causing mutation, validating diagnosis of OCA2. Currently, few reports have been published regarding this mutation site. It represents a new mutation site in OCA2 (NM_000275.2:c.863_886del), contributing to the genetic diversity of the OCA2.

Why humans evolved blue eyes

A surprising number of humans are equipped with a subpar eye model-featuring pale, colorful irides that are nowhere as good as the original dark ones at guarding the retina from sunlight and do, in fact, raise one's risk of eye disease. Here I apply evolutionary theory to understand why. I propose that the allele for human blue eyes, which arose just once, managed to spread from one individual to millions at an astonishing speed because it is a greenbeard. "Greenbeards"-imaginary genes, or groups of genes, that produce both a green beard and a behavior that favors other bearers of a green beard-have been deemed exceedingly unlikely to show up in the real world. And yet, as individuals who prefer blue eyes are more inclined to mate with blue-eyed partners and invest in blue-eyed offspring, any blue-eye preference (whether random or arising from the bias for colorful stimuli shared by all recognition systems) becomes rapidly linked to the blue-eye trait. Thus, blue eyes gain an edge by working like a peacock's colorful tail and a nestling's colorful mouth: twice self-reinforcing, "double runaway" evolution via sexual and parental selection. The blue-eye ornament gene, by binding to a behavior that favors other bearers of the blue-eye ornament gene, is ultimately recognizing and helping copies of itself in both kin and strangers-and greatly prospering, just like theory predicts.

A 65 kilobase deletion of the upstream TYR gene region in a family with oculocutaneous albinism type 1

Oculocutaneous albinism type 1 is caused by variants in the TYR (tyrosinase) gene. We describe a family with two affected sibs who inherited the pathogenic missense TYR variant c.1146C > A;p.(Asn382Lys) from their mother and a deletion encompassing 65 kilobase pairs of the upstream region of the gene between hg38 coordinates chr11:89110944 and chr11:89175770, from their father. The deletion likely arose by non-homologous recombination since the regions including the two deletion breakpoints share no sequence homology. The deletion contains a single enhancer element that is homologous to a 5' Tyr core regulatory element in the mouse. A luciferase reporter assay showed that this element had a positive regulatory activity. This represents to our knowledge the first deletion solely restricted to non-coding upstream sequences of the TYR gene. It is assumed that the deletion down-regulates expression of the TYR gene and is therefore pathogenic, allowing to establish the diagnosis of OCA 1 in the patients. This study underscores the need to extend the search for pathogenic variants to regulatory regions either by whole genome sequencing or by targeted next generation sequencing of a panel including entire genes (exons, introns, flanking sequences) in order to improve the diagnostic rate in patients with albinism.

Association of Genetic Polymorphisms in SLC45A2, TYR, HERC2, and SLC24A in African Women with Melasma: A Pilot Study

Melasma is a chronic skin disorder characterized by hyperpigmentation, predominantly affecting women with darker skin types, including those of African descent. This study investigates the association between genetic variants in SLC45A2, TYR, HERC2, and SLC24A5 genes and the severity of melasma in women of reproductive age. Forty participants were divided into two groups: twenty with facial melasma and twenty without. Deoxyribonucleic acid (DNA) was extracted from blood samples and genotyped using TaqMan assays to identify allele frequencies and genotype distributions. Significant associations were observed for the TYR gene (rs1042602), HERC2 gene (rs1129038), and SLC24A5 gene (rs1426654) polymorphisms, highlighting their potential roles in melasma susceptibility. For example, the rs1042602 Single Nucleotide Polymorphisms (SNP) in the TYR gene showed a strong association with melasma, with the AA genotype conferring a markedly increased risk. Similarly, the rs1129038 SNP in the HERC2 gene and the rs1426654 SNP in the SLC24A5 gene revealed significant genetic variations between groups in women of African descent. These findings underscore the influence of genetic polymorphisms on melasma's pathogenesis, emphasizing the need for personalized approaches to its treatment, particularly for women with darker skin types.

Machine learning derived retinal pigment score from ophthalmic imaging shows ethnicity is not biology

Few metrics exist to describe phenotypic diversity within ophthalmic imaging datasets, with researchers often using ethnicity as a surrogate marker for biological variability. We derived a continuous, measured metric, the retinal pigment score (RPS), that quantifies the degree of pigmentation from a colour fundus photograph of the eye. RPS was validated using two large epidemiological studies with demographic and genetic data (UK Biobank and EPIC-Norfolk Study) and reproduced in a Tanzanian, an Australian, and a Chinese dataset. A genome-wide association study (GWAS) of RPS from UK Biobank identified 20 loci with known associations with skin, iris and hair pigmentation, of which eight were replicated in the EPIC-Norfolk cohort. There was a strong association between RPS and ethnicity, however, there was substantial overlap between each ethnicity and the respective distributions of RPS scores. RPS decouples traditional demographic variables from clinical imaging characteristics. RPS may serve as a useful metric to quantify the diversity of the training, validation, and testing datasets used in the development of AI algorithms to ensure adequate inclusion and explainability of the model performance, critical in evaluating all currently deployed AI models. The code to derive RPS is publicly available at: https://github.com/uw-biomedical-ml/retinal-pigmentation-score .

Mapping chromatin interactions at melanoma susceptibility loci and cell-type specific dataset integration uncovers distant gene targets of cis-regulation

Genome-wide association studies (GWAS) of melanoma risk have identified 68 independent signals at 54 loci. For most loci, specific functional variants and their respective target genes remain to be established. Capture-HiC is an assay that links fine-mapped risk variants to candidate target genes by comprehensively mapping cell-type specific chromatin interactions. We performed a melanoma GWAS region-focused capture-HiC assay in human primary melanocytes to identify physical interactions between fine-mapped risk variants and potential causal melanoma susceptibility genes. Overall, chromatin interaction data alone nominated potential causal genes for 61 of the 68 melanoma risk signals, identifying many candidates beyond those reported by previous studies. We further integrated these data with cell-type specific epigenomic (chromatin state, accessibility), gene expression (eQTL/TWAS), DNA methylation (meQTL/MWAS), and massively parallel reporter assay (MPRA) data to prioritize potentially cis-regulatory variants and their respective candidate gene targets. From the set of fine-mapped variants across these loci, we identified 140 prioritized candidate causal variants linked to 195 candidate genes at 42 risk signals. In addition, we developed an integrative scoring system to facilitate candidate gene prioritization, integrating melanocyte and melanoma datasets. Notably, at several GWAS risk signals we observed long-range chromatin connections (500 kb to >1 Mb) with distant candidate target genes. We validated several such cis-regulatory interactions using CRISPR inhibition, providing evidence for known cancer driver genes MDM4 and CBL, as well as the SRY-box transcription factor SOX4, as likely melanoma risk genes.

Modeling recent positive selection using identity-by-descent segments

Recent positive selection can result in an excess of long identity-by-descent (IBD) haplotype segments overlapping a locus. The statistical methods that we propose here address three major objectives in studying selective sweeps: scanning for regions of interest, identifying possible sweeping alleles, and estimating a selection coefficient s. First, we implement a selection scan to locate regions with excess IBD rates. Second, we estimate the allele frequency and location of an unknown sweeping allele by aggregating over variants that are more abundant in an inferred outgroup with excess IBD rate versus the rest of the sample. Third, we propose an estimator for the selection coefficient and quantify uncertainty using the parametric bootstrap. Comparing against state-of-the-art methods in extensive simulations, we show that our methods are more precise at estimating s when s≥0.015. We also show that our 95% confidence intervals contain s in nearly 95% of our simulations. We apply these methods to study positive selection in European ancestry samples from the Trans-Omics for Precision Medicine project. We analyze eight loci where IBD rates are more than four standard deviations above the genome-wide median, including LCT where the maximum IBD rate is 35 standard deviations above the genome-wide median. Overall, we present robust and accurate approaches to study recent adaptive evolution without knowing the identity of the causal allele or using time series data.

Nonadditive Effects of Common Genetic Variants Have a Negligent Contribution to Cancer Heritability

BACKGROUND

Contribution of dominance effects to cancer heritability is unknown. We leveraged existing genome-wide association data for seven cancers to estimate the contribution of dominance effects to the heritability of individual cancer types.

METHODS

We estimated the proportion of phenotypic variation caused by dominance genetic effects using genome-wide association data for seven cancers (breast, colorectal, lung, melanoma, nonmelanoma skin, ovarian, and prostate) in a total of 166,772 cases and 284,824 controls.

RESULTS

We observed no evidence of a meaningful contribution of dominance effects to cancer heritability. By contrast, additive effects ranged between 0.11 and 0.34.

CONCLUSIONS

In line with studies of other human traits, the dominance effects of common genetic variants play a minimal role in cancer etiology.

IMPACT

These results support the assumption of an additive inheritance model when conducting cancer association studies with common genetic variants.

The fork remodeler helicase-like transcription factor in cancer development: all at once

The Helicase-like Transcription Factor (HLTF) is a member of the SNF2-family of fork remodelers, primarily studied for its capacity to provide DNA Damage Tolerance (DDT) and to induce replication fork reversal (RFR). HLTF is recruited at stalled forks where both its ATPase motor and HIP116 Rad5p N-terminal (HIRAN) domains are necessary for regulating its interaction with DNA. HIRAN bestows specificity to ssDNA 3'-end and imparts branch migration as well as DNA remodeling capabilities facilitating damage repair. Both expression regulation and mutation rate affect HLTF activity. Gene hypermethylation induces loss of HLTF function, in particular in colorectal cancer (CRC), implying a tumour suppressor role. Surprisingly, a correlation between hypermethylation and HLTF mRNA upregulation has also been observed, even within the same cancer type. In many cancers, both complex mutation patterns and the presence of gene Copy Number Variations (CNVs) have been reported. These conditions affect the amount of functional HLTF and question the physiological role of this fork remodeler. This review offers a systematic collection of the presently strewed information regarding HLTF, its structural and functional characteristics, the multiple roles in DDT and the regulation in cancer progression highlighting new research perspectives.

Skin pigmentation related variants in Mexican population and interaction effects on serum 25(OH)D concentration and vitamin D deficiency

Skin pigmentation is negatively associated with circulating vitamin D (VD) concentration. Therefore, genetic factors involved in skin pigmentation could influence the risk of vitamin D deficiency (VDD). We evaluated the impact genetic variants related to skin pigmentation on VD in Mexican population. This cross-sectional analysis included 848 individuals from the Health Worker Cohort Study (ratio males to females ~ 1:3). Eight genetic variants: rs16891982 (SLC45A2), rs12203592 (IRF4), rs1042602 and rs1126809 (TYR), rs1800404 (OCA2), rs12913832 (HERC2), rs1426654 (SLC24A5), and rs2240751 (MFSD12); involved in skin pigmentation were genotyped. Skin pigmentation was assessed by self-report. Linear and logistic regression were used to assess the association between the variants of interest and VD and VDD, as appropriate. In our study, eight genetic variants were associated with skin pigmentation. A genetic risk score built with the variants rs1426654 and rs224075 was associated with lower VD levels (β = - 1.38, 95% CI - 2.59, - 0.17, p = 0.025). Nevertheless, when examining gene-gene interactions, we observed that rs2240751 × rs12203592 were associated with VD levels (P interaction = 0.021). Whereas rs2240751 × rs12913832 (P interaction = 0.0001) were associated with VDD. Our results suggest that skin pigmentation-related gene variants are associated with lower VD levels in Mexican population. These results underscore the importance of considering genetic interactions when assessing the impact of genetic polymorphisms on VD levels.

Enhanced MC1R-signalling and pH modulation facilitate melanogenesis within late endosomes of BLOC-1-deficient melanocytes

Photoprotective melanins in the skin are synthesised by epidermal melanocytes within specialised lysosome-related organelles called melanosomes. Melanosomes coexist with lysosomes; thus, melanocytes employ specific trafficking machineries to ensure correct cargo delivery to either the endolysosomal system or maturing melanosomes. Mutations in some of the protein complexes required for melanogenic cargo delivery, such as biogenesis of lysosome-related organelles complex 1 (BLOC-1), result in hypopigmentation due to mistrafficking of cargo to endolysosomes. We show that hypopigmented BLOC-1-deficient melanocytes retain melanogenic capacity that can be enhanced by treatment with cAMP elevating agents despite the mislocalisation of melanogenic proteins. The melanin formed in BLOC-1-deficient melanocytes is not generated in melanosomes but rather within late endosomes/lysosomes to which some cargoes mislocalise. Although these organelles generally are acidic, a cohort of late endosomes/lysosomes have a sufficiently neutral pH to facilitate melanogenesis, perhaps due to mislocalised melanosomal transporters and melanogenic enzymes. Modulation of the pH of late endosomes/lysosomes by genetic manipulation or via treatment with lysosomotropic agents significantly enhances the melanin content of BLOC-1-deficient melanocytes. Our data suggest that upregulation of mistargeted cargoes can facilitate reprogramming of a subset of endolysosomes to generate some functions of lysosome-related organelles.

Predictive accuracy of genetic variants for eye color in a Kazakh population using the IrisPlex system

OBJECTIVE

This study assesses the accuracy of the IrisPlex system, a genetic eye color prediction tool for forensic analysis, in the Kazakh population. The study compares previously published genotypes of 515 Kazakh individuals from varied geographical and ethnohistorical contexts with phenotypic data on their eye color, introduced for the first time in this research.

RESULTS

The IrisPlex panel's effectiveness in predicting eye color in the Kazakh population was validated. It exhibited slightly lower accuracy than in Western European populations but was higher than in Siberian populations. The sensitivity was notably high for brown-eyed individuals (0.99), but further research is needed for blue and intermediate eye colors. This study establishes IrisPlex as a useful predictive tool in the Kazakh population and provides a basis for future investigations into the genetic basis of phenotypic variations in this diverse population.

Functional analysis of two mutation sites in the OCA2 gene

To analyse the genetic aetiology of a child with oculocutaneous albinism and to explore the effects of two mutation sites on the function of the OCA2 protein at the mRNA and protein levels via the use of recombinant carriers in vitro. Whole-exome sequencing (WES) and Sanger sequencing were used to analyse the pathogenic genes of the child and validate the mutations in the parents. pEGFP and phage vectors carrying wild-type and mutant OCA2 were constructed using the coding DNA sequence (CDS) of the whole gene-synthesized OCA2 as a template and transfected into HEK293T cells, after which expression analysis was performed. The child in this study was born with white skin, hair, eyelashes, and eyebrows and exhibited nystagmus. Genetic analysis indicated that the child carried two heterozygous mutations: c.1079C > T (p.Ser360Phe) of maternal origin and c.1095_1103delAGCACTGGC (p.Ala366_Ala368del) of paternal origin, conforming to an autosomal recessive inheritance pattern. In vitro analysis showed that the expression of the c.1079C > T (p.Ser360Phe) mutant did not significantly change at the mRNA level but did increase at the protein level, suggesting that the mutation may lead to enhanced protein stability, and the c.1095_1103delAGCACTGGC (p.Ala366_Ala368del) mutation resulted in the loss of three amino acids in exon 10, producing a truncated protein. In vitro expression analysis also revealed that the expression of the mutant gene was significantly downregulated at both the mRNA and protein levels, suggesting that the mutation can simultaneously produce truncated proteins and lead to protein degradation. This case study enriches the phenotypic spectrum of OCA2 gene disease. In vitro expression analysis confirmed that both mutations affect protein expression, providing a theoretical basis for analysing the pathogenicity of these two mutations.

The Chromatin Organization Close to SNP rs12913832, Involved in Eye Color Variation, Is Evolutionary Conserved in Vertebrates

The most significant genetic influence on eye color pigmentation is attributed to the intronic SNP rs12913832 in the HERC2 gene, which interacts with the promoter region of the contiguous OCA2 gene. This interaction, through the formation of a chromatin loop, modulates the transcriptional activity of OCA2, directly affecting eye color pigmentation. Recent advancements in technology have elucidated the precise spatial organization of the genome within the cell nucleus, with chromatin architecture playing a pivotal role in regulating various genome functions. In this study, we investigated the organization of the chromatin close to the HERC2/OCA2 locus in human lymphocyte nuclei using fluorescence in situ hybridization (FISH) and high-throughput chromosome conformation capture (Hi-C) data. The 3 Mb of genomic DNA that belonged to the chromosomal region 15q12-q13.1 revealed the presence of three contiguous chromatin loops, which exhibited a different level of compaction depending on the presence of the A or G allele in the SNP rs12913832. Moreover, the analysis of the genomic organization of the genes has demonstrated that this chromosomal region is evolutionarily highly conserved, as evidenced by the analysis of syntenic regions in species from other Vertebrate classes. Thus, the role of rs12913832 variant is relevant not only in determining the transcriptional activation of the OCA2 gene but also in the chromatin compaction of a larger region, underscoring the critical role of chromatin organization in the proper regulation of the involved genes. It is crucial to consider the broader implications of this finding, especially regarding the potential regulatory role of similar polymorphisms located within intronic regions, which do not influence the same gene by modulating the splicing process, but they regulate the expression of adjacent genes. Therefore, caution should be exercised when utilizing whole-exome sequencing for diagnostic purposes, as intron sequences may provide valuable gene regulation information on the region where they reside. Thus, future research efforts should also be directed towards gaining a deeper understanding of the precise mechanisms underlying the role and mode of action of intronic SNPs in chromatin loop organization and transcriptional regulation.

Single-cell profiling of MC1R-inhibited melanocytes

The human red hair color (RHC) trait is caused by increased pheomelanin (red-yellow) and reduced eumelanin (black-brown) pigment in skin and hair due to diminished melanocortin 1 receptor (MC1R) function. In addition, individuals harboring the RHC trait are predisposed to melanoma development. While MC1R variants have been established as causative of RHC and are a well-defined risk factor for melanoma, it remains unclear mechanistically why decreased MC1R signaling alters pigmentation and increases melanoma susceptibility. Here, we use single-cell RNA sequencing (scRNA-seq) of melanocytes isolated from RHC mouse models to define a MC1R-inhibited Gene Signature (MiGS) comprising a large set of previously unidentified genes which may be implicated in melanogenesis and oncogenic transformation. We show that one of the candidate MiGS genes, TBX3, a well-known anti-senescence transcription factor implicated in melanoma progression, binds both E-box and T-box elements to regulate genes associated with melanogenesis and senescence bypass. Our results provide key insights into further mechanisms by which melanocytes with reduced MC1R signaling may regulate pigmentation and offer new candidates of study toward understanding how individuals with the RHC phenotype are predisposed to melanoma.

Identification of Candidate Genes for Red-Eyed (Albinism) Domestic Guppies Using Genomic and Transcriptomic Analyses

Guppies are small tropical fish with brightly colored bodies and variable tail shapes. There are two phenotypes of domestic guppy eye color: red and black. The wild type is black-eyed. The main object of this study was to identify candidate genes for the red-eyed phenotype in domestic guppies. We hope to provide molecular genetic information for the development of new domestic guppy strains. Additionally, the results also contribute to basic research concerning guppies. In this study, 121 domestic guppies were used for genomic analysis (GWAS), and 44 genes were identified. Furthermore, 21 domestic guppies were used for transcriptomic analysis, and 874 differentially expressed genes (DEGs) were identified, including 357 upregulated and 517 downregulated genes. Through GO and KEGG enrichment, we identified some important terms or pathways mainly related to melanin biosynthesis and ion transport. qRT-PCR was also performed to verify the differential expression levels of four important candidate genes (TYR, OCA2, SLC45A2, and SLC24A5) between red-eyed and black-eyed guppies. Based on the results of genomic and transcriptomic analyses, we propose that OCA2 is the most important candidate gene for the red-eyed phenotype in guppies.

Integrative functional genomic analyses identify genetic variants influencing skin pigmentation in Africans

Skin color is highly variable in Africans, yet little is known about the underlying molecular mechanism. Here we applied massively parallel reporter assays to screen 1,157 candidate variants influencing skin pigmentation in Africans and identified 165 single-nucleotide polymorphisms showing differential regulatory activities between alleles. We combine Hi-C, genome editing and melanin assays to identify regulatory elements for MFSD12, HMG20B, OCA2, MITF, LEF1, TRPS1, BLOC1S6 and CYB561A3 that impact melanin levels in vitro and modulate human skin color. We found that independent mutations in an OCA2 enhancer contribute to the evolution of human skin color diversity and detect signals of local adaptation at enhancers of MITF, LEF1 and TRPS1, which may contribute to the light skin color of Khoesan-speaking populations from Southern Africa. Additionally, we identified CYB561A3 as a novel pigmentation regulator that impacts genes involved in oxidative phosphorylation and melanogenesis. These results provide insights into the mechanisms underlying human skin color diversity and adaptive evolution.

Whole Exome Sequencing as a First-Line Molecular Genetic Test in Developmental and Epileptic Encephalopathies

Developmental and epileptic encephalopathies (DEE) are severe neurodevelopmental disorders characterized by recurrent, usually early-onset, epileptic seizures accompanied by developmental impairment often related to both underlying genetic etiology and abnormal epileptiform activity. Today, next-generation sequencing technologies (NGS) allow us to sequence large portions of DNA quickly and with low costs. The aim of this study is to evaluate the use of whole-exome sequencing (WES) as a first-line molecular genetic test in a sample of subjects with DEEs characterized by early-onset drug-resistant epilepsies, associated with global developmental delay and/or intellectual disability (ID). We performed 82 WESs, identifying 35 pathogenic variants with a detection rate of 43%. The identified variants were highlighted on 29 different genes including, 3 new candidate genes (KCNC2, STXBP6, DHRS9) for DEEs never identified before. In total, 23 out of 35 (66%) de novo variants were identified. The most frequently identified type of inheritance was autosomal dominant de novo (60%) followed by autosomal recessive in homozygosity (17%) and heterozygosity (11%), autosomal dominant inherited from parental mosaicism (6%) and X-linked dominant de novo (6%). The most frequent mutations identified were missense (75%) followed by frameshift deletions (16%), frameshift duplications (5%), and splicing mutations (3%). Considering the results obtained in the present study we support the use of WES as a form of first-line molecular genetic testing in DEEs.

Genetic landscape of forensic DNA phenotyping markers among Mediterranean populations

Forensic DNA Phenotyping can reveal the appearance of an unknown individual by predicting the External Visible Characteristics (EVC) from DNA obtained at the crime scene. Our aim is to characterize the genetic landscape of Human identification markers responsible for EVC among Mediterranean populations compared to other worldwide groups. We conducted an exhaustive search for genes involved in EVC variation. Then, variants located on these genes were extracted from public genotypic data of Mediterranean, American, African and East Asiatic populations. The genetic landscape of these Human identification markers, their allelic distribution and admixture analyses, were determined using plink, R and ADMIXTURE softwares. Our results showed that the Mediterranean populations appear close to the Mexican populations and distinguished from sub Saharan African populations living in the USA and from East Asiatic populations. We highlighted a total of 103454 common variants shared between the studied populations and among them, 25 common variants associated with EVC. Interestingly, genotype frequencies results showed that the rs17646946, rs13016869, rs977588, rs1805008 and rs2240751 variants located respectively in the TCHH, PRKCE, OCA2, MC1R and MFSD12 genes are significantly different between the Mediterranean and Asiatic populations. The genotype frequencies of the variants rs977589 and rs7179994 located in the OCA2 gene, and of rs12913832 and rs2240751 located respectively in HERC2 and MFSD12 genes are significantly different between the Mediterranean and American populations. Our work generates a large number of EVC variants that could be a valuable resource for future studies in the forensic field.

Whole Genome Resequencing Reveals Selection Signals Related to Wool Color in Sheep

Wool color is controlled by a variety of genes. Although the gene regulation of some wool colors has been studied in relative depth, there may still be unknown genetic variants and control genes for some colors or different breeds of wool that need to be identified and recognized by whole genome resequencing. Therefore, we used whole genome resequencing data to compare and analyze sheep populations of different breeds by population differentiation index and nucleotide diversity ratios (Fst and θπ ratio) as well as extended haplotype purity between populations (XP-EHH) to reveal selection signals related to wool coloration in sheep. Screening in the non-white wool color group (G1 vs. G2) yielded 365 candidate genes, among which PDE4B, GMDS, GATA1, RCOR1, MAPK4, SLC36A1, and PPP3CA were associated with the formation of non-white wool; an enrichment analysis of the candidate genes yielded 21 significant GO terms and 49 significant KEGG pathways (p < 0.05), among which 17 GO terms and 21 KEGG pathways were associated with the formation of non-white wool. Screening in the white wool color group (G2 vs. G1) yielded 214 candidate genes, including ABCD4, VSX2, ITCH, NNT, POLA1, IGF1R, HOXA10, and DAO, which were associated with the formation of white wool; an enrichment analysis of the candidate genes revealed 9 significant GO-enriched pathways and 19 significant KEGG pathways (p < 0.05), including 5 GO terms and 12 KEGG pathways associated with the formation of white wool. In addition to furthering our understanding of wool color genetics, this research is important for breeding purposes.

Specific Learning Disorders: Variation Analysis of 15 Candidate Genes in 9 Multiplex Families

Background and Objectives: Specific Learning Disorder (SLD) is a complex neurobiological disorder characterized by a persistent difficult in reading (dyslexia), written expression (dysgraphia), and mathematics (dyscalculia). The hereditary and genetic component is one of the underlying causes of SLD, but the relationship between genes and the environment should be considered. Several genetic studies were performed in different populations to identify causative genes. Materials and Methods: Here, we show the analysis of 9 multiplex families with at least 2 individuals diagnosed with SLD per family, with a total of 37 persons, 21 of whom are young subjects with SLD, by means of Next-Generation Sequencing (NGS) to identify possible causative mutations in a panel of 15 candidate genes: CCPG1, CYP19A1, DCDC2, DGKI, DIP2A, DYM, GCFC2, KIAA0319, MC5R, MRPL19, NEDD4L, PCNT, PRMT2, ROBO1, and S100B. Results: We detected, in eight families out nine, SNP variants in the DGKI, DIP2A, KIAA0319, and PCNT genes, even if in silico analysis did not show any causative effect on this behavioral condition. In all cases, the mutation was transmitted by one of the two parents, thus excluding the case of de novo mutation. Moreover, the parent carrying the allelic variant transmitted to the children, in six out of seven families, reports language difficulties. Conclusions: Although the present results cannot be considered conclusive due to the limited sample size, the identification of genetic variants in the above genes can provide input for further research on the same, as well as on other genes/mutations, to better understand the genetic basis of this disorder, and from this perspective, to better understand also the neuropsychological and social aspects connected to this disorder, which affects an increasing number of young people.

Forensic DNA Phenotyping: Genes and Genetic Variants for Eye Color Prediction

In recent decades, the use of genetic polymorphisms related to specific phenotypes, such as eye color, has greatly contributed to the development of the research field called forensic DNA phenotyping (FDP), enabling the investigators of crime cases to reduce the number of suspects, making their work faster and more precise. Eye color is a polygenic phenotype, and many genetic variants have been highlighted, with the major contributor being the HERC2-OCA2 locus, where many single nucleotide variations (SNPs) were identified. Interestingly, the HERC2-OCA2 locus, containing the intronic SNP rs12913832, the major eye color determinant, shows a high level of evolutionary conservation across many species of vertebrates. Currently, there are some genetic panels to predict eye color by genomic DNA analysis, even if the exact role of the SNP variants in the formation of eye color is still poorly understood, with a low level of predictivity in the so-called intermediate eye color. Many variants in OCA2, HERC2, and other genes lie in introns or correspond to synonymous variants, highlighting greater complexity in the mechanism of action of such genes than a simple missense variation. Here, we show the main genes involved in oculocutaneous pigmentation and their structural and functional features, as well as which genetic variants show the highest level of eye color predictivity in currently used FDP assays. Despite the great recent advances and impact of FDP in criminal cases, it is necessary to enhance scientific research to better understand the mechanism of action behind each genetic variant involved in eye color, with the goal of obtaining higher levels of prediction.

Ethnicity is not biology: retinal pigment score to evaluate biological variability from ophthalmic imaging using machine learning

Background

Few metrics exist to describe phenotypic diversity within ophthalmic imaging datasets, with researchers often using ethnicity as an inappropriate marker for biological variability.

Methods

We derived a continuous, measured metric, the retinal pigment score (RPS), that quantifies the degree of pigmentation from a colour fundus photograph of the eye. RPS was validated using two large epidemiological studies with demographic and genetic data (UK Biobank and EPIC-Norfolk Study).

Findings

A genome-wide association study (GWAS) of RPS from UK Biobank identified 20 loci with known associations with skin, iris and hair pigmentation, of which 8 were replicated in the EPIC-Norfolk cohort. There was a strong association between RPS and ethnicity, however, there was substantial overlap between each ethnicity and the respective distributions of RPS scores.

Interpretation

RPS serves to decouple traditional demographic variables, such as ethnicity, from clinical imaging characteristics. RPS may serve as a useful metric to quantify the diversity of the training, validation, and testing datasets used in the development of AI algorithms to ensure adequate inclusion and explainability of the model performance, critical in evaluating all currently deployed AI models. The code to derive RPS is publicly available at: https://github.com/uw-biomedical-ml/retinal-pigmentation-score.

Funding

The authors did not receive support from any organisation for the submitted work.

Analysis of genetic dominance in the UK Biobank

Classical statistical genetics theory defines dominance as any deviation from a purely additive, or dosage, effect of a genotype on a trait, which is known as the dominance deviation. Dominance is well documented in plant and animal breeding. Outside of rare monogenic traits, however, evidence in humans is limited. We systematically examined common genetic variation across 1060 traits in a large population cohort (UK Biobank, N = 361,194 samples analyzed) for evidence of dominance effects. We then developed a computationally efficient method to rapidly assess the aggregate contribution of dominance deviations to heritability. Lastly, observing that dominance associations are inherently less correlated between sites at a genomic locus than their additive counterparts, we explored whether they may be leveraged to identify causal variants more confidently.

Loss of MC1R signaling implicates TBX3 in pheomelanogenesis and melanoma predisposition

The human Red Hair Color (RHC) trait is caused by increased pheomelanin (red-yellow) and reduced eumelanin (black-brown) pigment in skin and hair due to diminished melanocortin 1 receptor (MC1R) function. In addition, individuals harboring the RHC trait are predisposed to melanoma development. While MC1R variants have been established as causative of RHC and are a well-defined risk factor for melanoma, it remains unclear mechanistically why decreased MC1R signaling alters pigmentation and increases melanoma susceptibility. Here, we use single-cell RNA-sequencing (scRNA-seq) of melanocytes isolated from RHC mouse models to reveal a Pheomelanin Gene Signature (PGS) comprising genes implicated in melanogenesis and oncogenic transformation. We show that TBX3, a well-known anti-senescence transcription factor implicated in melanoma progression, is part of the PGS and binds both E-box and T-box elements to regulate genes associated with melanogenesis and senescence bypass. Our results provide key insights into mechanisms by which MC1R signaling regulates pigmentation and how individuals with the RHC phenotype are predisposed to melanoma.

Association between Variants in the OCA2-HERC2 Region and Blue Eye Colour in HERC2 rs12913832 AA and AG Individuals

The OCA2-HERC2 region is strongly associated with human pigmentation, especially eye colour. The HERC2 SNP rs12913832 is currently the best-known predictor for blue and brown eye colour. However, in a previous study we found that 43 of 166 Norwegians with the brown eye colour genotype rs12913832:AA or AG, did not have the expected brown eye colour. In this study, we carried out massively parallel sequencing of a ~500 kbp HERC2-OCA2 region in 94 rs12913832:AA and AG Norwegians (43 blue-eyed and 51 brown-eyed) to search for novel blue eye colour variants. The new candidate variants were subsequently typed in a Norwegian biobank population (total n = 519) for population specific association analysis. We identified five new variants, rs74409036:A, rs78544415:T, rs72714116:T, rs191109490:C and rs551217952:C, to be the most promising candidates for explaining blue eye colour in individuals with the rs12913832:AA and AG genotype. Additionally, we confirmed the association of the missense variants rs74653330:T and rs121918166:T with blue eye colour, and observed lighter skin colour in rs74653330:T individuals. In total, 37 (86%) of the 43 blue-eyed rs12913832:AA and AG Norwegians could potentially be explained by these seven variants, and we suggest including them in future prediction models.

Massively parallel reporter assays and variant scoring identified functional variants and target genes for melanoma loci and highlighted cell-type specificity

The most recent genome-wide association study (GWAS) of cutaneous melanoma identified 54 risk-associated loci, but functional variants and their target genes for most have not been established. Here, we performed massively parallel reporter assays (MPRAs) by using malignant melanoma and normal melanocyte cells and further integrated multi-layer annotation to systematically prioritize functional variants and susceptibility genes from these GWAS loci. Of 1,992 risk-associated variants tested in MPRAs, we identified 285 from 42 loci (78% of the known loci) displaying significant allelic transcriptional activities in either cell type (FDR < 1%). We further characterized MPRA-significant variants by motif prediction, epigenomic annotation, and statistical/functional fine-mapping to create integrative variant scores, which prioritized one to six plausible candidate variants per locus for the 42 loci and nominated a single variant for 43% of these loci. Overlaying the MPRA-significant variants with genome-wide significant expression or methylation quantitative trait loci (eQTLs or meQTLs, respectively) from melanocytes or melanomas identified candidate susceptibility genes for 60% of variants (172 of 285 variants). CRISPRi of top-scoring variants validated their cis-regulatory effect on the eQTL target genes, MAFF (22q13.1) and GPRC5A (12p13.1). Finally, we identified 36 melanoma-specific and 45 melanocyte-specific MPRA-significant variants, a subset of which are linked to cell-type-specific target genes. Analyses of transcription factor availability in MPRA datasets and variant-transcription-factor interaction in eQTL datasets highlighted the roles of transcription factors in cell-type-specific variant functionality. In conclusion, MPRAs along with variant scoring effectively prioritized plausible candidates for most melanoma GWAS loci and highlighted cellular contexts where the susceptibility variants are functional.

Predicting Eye and Hair Color in a Turkish Population Using the HIrisPlex System

Forensic DNA Phenotyping (FDP) can reveal the appearance of an unknown individual by predicting the ancestry, phenotype (i.e., hair, eye, skin color), and age from DNA obtained at the crime scene. The HIrisPlex system has been developed to simultaneously predict eye and hair color. However, the prediction accuracy of the system needs to be assessed for the tested population before implementing FDP in casework. In this study, we evaluated the performance of the HIrisPlex system on 149 individuals from the Turkish population. We applied the single-based extension (SNaPshot chemistry) method and used the HIrisPlex online tool to test the prediction of the eye and hair colors. The accuracy of the HIrisPlex system was assessed through the calculation of the area under the receiver characteristic operating curves (AUC), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). The results showed that the proposed method successfully predicted the eye and hair color, especially for blue (100%) and brown (95.60%) eye and black (95.23) and brown (98.94) hair colors. As observed in previous studies, the system failed to predict intermediate eye color, representing 25% in our cohort. The majority of incorrect predictions were observed for blond hair color (40.7%). Previous HIrisPlex studies have also noted difficulties with these phenotypes. Our study shows that the HIrisPlex system can be applied to forensic casework in Turkey with careful interpretation of the data, particularly intermediate eye color and blond hair color.

Uncovering the extensive trade-off between adaptive evolution and disease susceptibility

Favored mutations in the human genome may make the carriers adapt to changing environments and lifestyles but also susceptible to specific diseases. The scale and details of the trade-off between adaptive evolution and disease susceptibility are unclear because most favored mutations in different populations remain unidentified. As no statistical test can discriminate favored mutations from nearby hitchhiking neutral ones, we report a deep-learning network (DeepFavored) to integrate multiple statistical tests and divide identifying favored mutations into two subtasks. We identify favored mutations in three human populations and analyzed the correlation between favored/hitchhiking mutations and genome-wide association study (GWAS) sites. Both favored and hitchhiking neutral mutations are enriched in GWAS sites with population-specific features, and the enrichment and population specificity are prominent in genes in specific Gene Ontology (GO) terms. These provide evidence for extensive and population-specific trade-offs between adaptive evolution and disease susceptibility. The unveiled scale helps understand and investigate differences and diseases of humans.

Applicability of the IrisPlex system for eye color prediction in an admixed population from Argentina

Eye color prediction based on an individual's genetic information is of interest in the field of forensic genetics. In recent years, researchers have studied different genes and markers associated with this externally visible characteristic and have developed methods for its prediction. The IrisPlex represents a validated tool for homogeneous populations, though its applicability in populations of mixed ancestry is limited, mainly regarding the prediction of intermediate eye colors. With the aim of validating the applicability of this system in an admixed population from Argentina (n = 302), we analyzed the six single nucleotide variants used in that multiplex for eye color and four additional SNPs, and evaluated its prediction ability. We also performed a genotype-phenotype association analysis. This system proved to be useful when dealing with the extreme ends of the eye color spectrum (blue and brown) but presented difficulties in determining the intermediate phenotypes (green), which were found in a large proportion of our population. We concluded that these genetic tools should be used with caution in admixed populations and that more studies are required in order to improve the prediction of intermediate phenotypes.

A new approach to broaden the range of eye colour identifiable by IrisPlex in DNA phenotyping

IrisPlex system represents the most popular model for eye colour prediction. Based on six polymorphisms this model provides very accurate predictions that strongly depend on the definition of eye colour phenotypes. The aim of the present study was to introduce a new approach to improve eye colour prediction using the well-validated IrisPlex system. A sample of 238 individuals from a Southern Italian population was collected and for each of them a high-resolution image of eye was obtained. By quantifying eye colour variation into CIELAB space several clustering algorithms were applied for eye colour classification. Predictions with the IrisPlex model were obtained using eye colour categories defined by both visual inspection and clustering algorithms. IrisPlex system predicted blue and brown eye colour with high accuracy while it was inefficient in the prediction of intermediate eye colour. Clustering-based eye colour resulted in a significantly increased accuracy of the model especially for brown eyes. Our results confirm the validity of the IrisPlex system for forensic purposes. Although the quantitative approach here proposed for eye colour definition slightly improves its prediction accuracy, further research is still required to improve the model particularly for the intermediate eye colour prediction.

QTL Mapping for Age-Related Eye Pigmentation in the Pink-Eyed Dilution Castaneus Mutant Mouse

Pink-eyed dilution castaneus (Oca2p-cas) is a mutant gene on mouse chromosome 7 that arose spontaneously in wild Mus musculus castaneus. Homozygotes for Oca2p-cas exhibit pink eyes and a light gray coat throughout life. In an ordinary mutant strain carrying Oca2p-cas, we previously discovered a novel spontaneous mutation that gradually increases melanin pigmentation in the eyes and coat with aging, and we developed a novel mutant strain that was fixed for the novel phenotype. The purpose of this study was to map major quantitative trait loci (QTLs) for the novel pigmentation phenotype and for expression levels of four important melanogenesis genes, microphthalmia-associated transcription factor (Mitf), tyrosinase (Tyr), tyrosinase-related protein-1 (Tyrp1) and dopachrome tautomerase (Dct). We developed 69 DNA markers and created 303 F2 mice from two reciprocal crosses between novel and ordinary mutant strains. The QTL analysis using a selective genotyping strategy revealed a significant QTL for eye pigmentation between 34 and 64 Mb on chromosome 13. This QTL explained approximately 20% of the phenotypic variance. The QTL allele derived from the novel strain increased pigmentation. Although eye pigmentation was positively correlated with Dct expression, no expression QTLs were found, suggesting that the pigmentation QTL on chromosome 13 may not be directly in the pathway of any of the four melanogenesis genes. This study is the first step toward identifying a causal gene for the novel spontaneous phenotype in mice and is expected to discover a new regulatory mechanism for complex melanin biosynthesis during aging.

Investigating the genetic architecture of eye colour in a Canadian cohort

Eye color is highly variable in populations with European ancestry, ranging from low to high quantities of melanin in the iris. Polymorphisms in the HERC2/OCA2 locus have the largest effect on eye color in these populations, although other genomic regions also influence eye color. We performed genome-wide association studies of eye color in a Canadian cohort of European ancestry (N = 5,641) and investigated candidate causal variants. We uncovered several candidate causal signals in the HERC2/OCA2 region, whereas other loci likely harbor a single causal signal. We observed colocalization of eye color signals with the expression or methylation profiles of cultured primary melanocytes. Genetic correlations of eye and hair color suggest high genome-wide pleiotropy, but locus-level differences in the genetic architecture of both traits. Overall, we provide a better picture of the polymorphisms underpinning eye color variation, which may be a consequence of specific molecular processes in the iris melanocytes.

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Genome-wide association studies of eye color in 5,641 participants

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Multiple independent candidate causal variants were identified across HERC2/OCA2

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Single candidate causal variants observed on or near IRF4, SLC24A4, TYR, and TYRP1

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Colocalization of eye color signals with expression and methylation profiles

The landscape of GWAS validation; systematic review identifying 309 validated non-coding variants across 130 human diseases

Background

The remarkable growth of genome-wide association studies (GWAS) has created a critical need to experimentally validate the disease-associated variants, 90% of which involve non-coding variants.

Methods

To determine how the field is addressing this urgent need, we performed a comprehensive literature review identifying 36,676 articles. These were reduced to 1454 articles through a set of filters using natural language processing and ontology-based text-mining. This was followed by manual curation and cross-referencing against the GWAS catalog, yielding a final set of 286 articles.

Results

We identified 309 experimentally validated non-coding GWAS variants, regulating 252 genes across 130 human disease traits. These variants covered a variety of regulatory mechanisms. Interestingly, 70% (215/309) acted through cis-regulatory elements, with the remaining through promoters (22%, 70/309) or non-coding RNAs (8%, 24/309). Several validation approaches were utilized in these studies, including gene expression (n = 272), transcription factor binding (n = 175), reporter assays (n = 171), in vivo models (n = 104), genome editing (n = 96) and chromatin interaction (n = 33).

Conclusions

This review of the literature is the first to systematically evaluate the status and the landscape of experimentation being used to validate non-coding GWAS-identified variants. Our results clearly underscore the multifaceted approach needed for experimental validation, have practical implications on variant prioritization and considerations of target gene nomination. While the field has a long way to go to validate the thousands of GWAS associations, we show that progress is being made and provide exemplars of validation studies covering a wide variety of mechanisms, target genes, and disease areas.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01216-w.

Zebrafish Syndromic Albinism Models as Tools for Understanding and Treating Pigment Cell Disease in Humans

Simple Summary

Zebrafish (Danio rerio) is an emerging model for studying many diseases, including disorders originating in black pigment cells, melanocytes. In this review of the melanocyte literature, we discuss the current knowledge of melanocyte biology relevant to understanding different forms of albinism and the potential of the zebrafish model system for finding novel mechanisms and treatments.

Abstract

Melanin is the pigment that protects DNA from ultraviolet (UV) damage by absorbing excess energy. Melanin is produced in a process called melanogenesis. When melanogenesis is altered, diseases such as albinism result. Albinism can result in an increased skin cancer risk. Conversely, black pigment cell (melanocyte) development pathways can be misregulated, causing excessive melanocyte growth that leads to melanoma (cancer of melanocytes). Zebrafish is an emerging model organism used to study pigment disorders due to their high fecundity, visible melanin development in melanophores (melanocytes in mammals) from 24 h post-fertilization, and conserved melanogenesis pathways. Here, we reviewed the conserved developmental pathways in zebrafish melanophores and mammalian melanocytes. Additionally, we summarized the progress made in understanding pigment cell disease and evidence supporting the strong potential for using zebrafish to find novel treatment options for albinism.

Candidate Genes in Bull Semen Production Traits: An Information Approach Review

Semen quality plays a crucial role in the successful implementation of breeding programs, especially where artificial insemination (AI) is practiced. Bulls with good semen traits have good fertility and can produce a volume of high semen per ejaculation. The aim of this review is to use an information approach to highlight candidate genes and their relation to bull semen production traits. The use of genome-wide association studies (GWAS) has been demonstrated to be successful in identifying genomic regions and individual variations associated with production traits. Studies have reported over 40 genes associated with semen traits using Illumina BeadChip single-nucleotide polymorphism (SNPs).

Epigenetics of alcohol-related liver diseases

Alcohol-related liver disease (ARLD) is a primary cause of chronic liver disease in the United States. Despite advances in the diagnosis and management of ARLD, it remains a major public health problem associated with significant morbidity and mortality, emphasising the need to adopt novel approaches to the study of ARLD and its complications. Epigenetic changes are increasingly being recognised as contributing to the pathogenesis of multiple disease states. Harnessing the power of innovative technologies for the study of epigenetics (e.g., next-generation sequencing, DNA methylation assays, histone modification profiling and computational techniques like machine learning) has resulted in a seismic shift in our understanding of the pathophysiology of ARLD. Knowledge of these techniques and advances is of paramount importance for the practicing hepatologist and researchers alike. Accordingly, in this review article we will summarise the current knowledge about alcohol-induced epigenetic alterations in the context of ARLD, including but not limited to, DNA hyper/hypo methylation, histone modifications, changes in non-coding RNA, 3D chromatin architecture and enhancer-promoter interactions. Additionally, we will discuss the state-of-the-art techniques used in the study of ARLD (e.g. single-cell sequencing). We will also highlight the epigenetic regulation of chemokines and their proinflammatory role in the context of ARLD. Lastly, we will examine the clinical applications of epigenetics in the diagnosis and management of ARLD.

Different Pigmentation Risk Loci for High-Risk Monosomy 3 and Low-Risk Disomy 3 Uveal Melanomas

BACKGROUND

Uveal melanoma (UM), a rare malignant tumor of the eye, is predominantly observed in populations of European ancestry. UMs carrying a monosomy 3 (M3) frequently relapse mainly in the liver, whereas UMs with disomy 3 (D3) are associated with more favorable outcome. Here, we explored the UM genetic predisposition factors in a large genome-wide association study (GWAS) of 1142 European UM patients and 882 healthy controls .

METHODS

We combined 2 independent datasets (Global Screening Array) with the dataset described in a previously published GWAS in UM (Omni5 array), which were imputed separately and subsequently merged. Patients were stratified according to their chromosome 3 status, and identified UM risk loci were tested for differential association with M3 or D3 subgroups. All statistical tests were 2-sided.

RESULTS

We recapitulated the previously identified risk locus on chromosome 5 on CLPTM1L (rs421284: odds ratio [OR] =1.58, 95% confidence interval [CI] = 1.35 to 1.86; P = 1.98 × 10-8) and identified 2 additional risk loci involved in eye pigmentation: IRF4 locus on chromosome 6 (rs12203592: OR = 1.76, 95% CI = 1.44 to 2.16; P = 3.55 × 10-8) and HERC2 locus on chromosome 15 (rs12913832: OR= 0.57, 95% CI = 0.48 to 0.67; P = 1.88 × 10-11). The IRF4 rs12203592 single-nucleotide polymorphism was found to be exclusively associated with risk for the D3 UM subtype (ORD3 = 2.73, 95% CI = 1.87 to 3.97; P = 1.78 × 10-7), and the HERC2 rs12913832 single-nucleotide polymorphism was exclusively associated with risk for the M3 UM subtype (ORM3 = 2.43, 95% CI = 1.79 to 3.29; P = 1.13 × 10-8). However, the CLPTM1L risk locus was equally statistically significant in both subgroups.

CONCLUSIONS

This work identified 2 additional UM risk loci known for their role in pigmentation. Importantly, we demonstrate that UM tumor biology and metastatic potential are influenced by patients' genetic backgrounds.

Study on the Correlation Between Iris Characteristics and Schizophrenia

BACKGROUND

Recently, researchers have conducted many studies on the potential contribution of the retina and other eye structures on schizophrenia. This study aimed to evaluate differences in iris characteristics between patients with schizophrenia and healthy individuals so as to find more easily accessible and easily measurable biomarkers with a view to improving clinical assessments and furthering our understanding of the disease.

METHODS

Overall, 80 patients with schizophrenia and 52 healthy individuals were included in the case group and the control group, respectively. Iris images were collected from all subjects to compare differences in the structure and color of the iris. The Positive and Negative Symptom Scale (PANSS) and the Modified Overt Aggression Scale (MOAS) were used to evaluate the clinical symptoms and characteristics of 45 first-episode untreated schizophrenics, and analyzed correlations between iris characteristics and schizophrenia symptoms.

RESULTS

There were significant differences in iris crypts (P<0.05) and pigment spots (P<0.01) between the case and control group, but no significant difference was found in iris wrinkles (P<0.05). The logistic regression analysis demonstrated that the total iris crypts [odds ratio (OR) 1.166, 95% confidence interval (CI) 1.022-1.330] and total iris pigment spots (OR 1.815, 95% CI 1.186-2.775) increased the risk of suffering from schizophrenia. Furthermore, it was demonstrated that the number of iris crypts was positively associated with the MOAS score (r=0.474, P<0.01). Moreover, the number of the iris pigment spots (r=0.395, P<0.01) and wrinkles (r=0.309, P<0.05) were positively correlated with the subjects' negative symptom scores, respectively.

CONCLUSION

Iris crypts and pigment spots were identified as potential biomarkers for detecting schizophrenia. In patients with first-episode untreated schizophrenia, iris characteristics may help psychiatrists to identify the illness and its severity, and to detect characteristic clinical symptoms.

Further insight into the global variability of the OCA2-HERC2 locus for human pigmentation from multiallelic markers

The OCA2-HERC2 locus is responsible for the greatest proportion of eye color variation in humans. Numerous studies extensively described both functional SNPs and associated patterns of variation over this region. The goal of our study is to examine how these haplotype structures and allelic associations vary when highly variable markers such as microsatellites are used. Eleven microsatellites spanning 357 Kb of OCA2-HERC2 genes are analyzed in 3029 individuals from worldwide populations. We found that several markers display large differences in allele frequency (10% to 35% difference) among Europeans, East Asians and Africans. In Europe, the alleles showing increased frequency can also discriminate individuals with (IrisPlex) predicted blue and brown eyes. Distinct haplotypes are identified around the variants C and T of the functional SNP rs12913832 (associated to blue eyes), with linkage disequilibrium r² values significant up to 237 Kb. The haplotype carrying the allele rs12913832 C has high frequency (76%) in blue eye predicted individuals (30% in brown eye predicted individuals), while the haplotype associated to the allele rs12913832 T is restricted to brown eye predicted individuals. Finally, homozygosity values reach levels of 91% near rs12913832. Odds ratios show values of 4.2, 7.4 and 10.4 for four markers around rs12913832 and 7.1 for their core haplotype. Hence, this study provides an example on the informativeness of multiallelic markers that, despite their current limited potential contribution to forensic eye color prediction, supports the use of microsatellites for identifying causing variants showing similar genetic features and history.

Predicting eye and hair colour in a Norwegian population using Verogen's ForenSeq™ DNA signature prep kit

Prediction of eye and hair colour from DNA can be an important investigative tool in forensic cases if conventional DNA profiling fails to match DNA from any known suspects or cannot obtain a hit in a DNA database. The HIrisPlex model for simultaneous eye and hair colour predictions was developed for forensic usage. To genotype a DNA sample, massively parallel sequencing (MPS) has brought new possibilities to the analysis of forensic DNA samples. As part of an in-house validation, this study presents the genotyping and predictive performance of the HIrisPlex SNPs in a Norwegian study population, using Verogen's ForenSeq™ DNA Signature Prep Kit on the MiSeq FGx system and the HIrisPlex webtool. DNA-profiles were successfully typed with DNA input down to 125 pg. In samples with DNA input < 125 pg, false homozygotes were observed with as many as 92 reads. Prediction accuracies in terms of AUC were high for red (0.97) and black (0.93) hair colours, as well as blue (0.85) and brown (0.94) eye colours. The AUCs for blond (0.72) and brown (0.70) hair colour were considerably lower. None of the individuals was predicted to have intermediate eye colour. Therefore, the error rates of the overall eye colour predictions were 37% with no predictive probability threshold (pmax) and 26% with a probability threshold of 0.7. We also observed that more than half of the incorrect predictions were for individuals carrying the rs12913832 GG genotype. For hair colour, 65% of the individuals were correctly predicted when using the highest probability category approach. The main error was observed for individuals with brown hair colour that were predicted to have blond hair. Utilising the prediction guide approach increased the correct predictions to 75%. Assessment of phenotype-genotype associations of eye colours using a quantitative eye colour score (PIE-score), revealed that rs12913832 AA individuals of Norwegian descent had statistically significantly higher PIE-score (less brown eye colour) than individuals of non-northern European descent. To our knowledge, this has not been reported in other studies. Our study suggests that careful assessment of the target population prior to the implementation of forensic DNA phenotyping to case work is beneficial.

A large Canadian cohort provides insights into the genetic architecture of human hair colour

Hair colour is a polygenic phenotype that results from differences in the amount and ratio of melanins located in the hair bulb. Genome-wide association studies (GWAS) have identified many loci involved in the pigmentation pathway affecting hair colour. However, most of the associated loci overlap non-protein coding regions and many of the molecular mechanisms underlying pigmentation variation are still not understood. Here, we conduct GWAS meta-analyses of hair colour in a Canadian cohort of 12,741 individuals of European ancestry. By performing fine-mapping analyses we identify candidate causal variants in pigmentation loci associated with blonde, red and brown hair colour. Additionally, we observe colocalization of several GWAS hits with expression and methylation quantitative trait loci (QTLs) of cultured melanocytes. Finally, transcriptome-wide association studies (TWAS) further nominate the expression of EDNRB and CDK10 as significantly associated with hair colour. Our results provide insights on the mechanisms regulating pigmentation biology in humans.

GenNet framework: interpretable deep learning for predicting phenotypes from genetic data

Applying deep learning in population genomics is challenging because of computational issues and lack of interpretable models. Here, we propose GenNet, a novel open-source deep learning framework for predicting phenotypes from genetic variants. In this framework, interpretable and memory-efficient neural network architectures are constructed by embedding biologically knowledge from public databases, resulting in neural networks that contain only biologically plausible connections. We applied the framework to seventeen phenotypes and found well-replicated genes such as HERC2 and OCA2 for hair and eye color, and novel genes such as ZNF773 and PCNT for schizophrenia. Additionally, the framework identified ubiquitin mediated proteolysis, endocrine system and viral infectious diseases as most predictive biological pathways for schizophrenia. GenNet is a freely available, end-to-end deep learning framework that allows researchers to develop and use interpretable neural networks to obtain novel insights into the genetic architecture of complex traits and diseases.

van Hilten and colleagues present GenNet, a deep-learning framework for predicting phenotype from genetic data. This framework generates interpretable neural networks that provide insight into the genetic basis of complex traits and diseases.

Cell-type-specific meQTLs extend melanoma GWAS annotation beyond eQTLs and inform melanocyte gene-regulatory mechanisms

Although expression quantitative trait loci (eQTLs) have been powerful in identifying susceptibility genes from genome-wide association study (GWAS) findings, most trait-associated loci are not explained by eQTLs alone. Alternative QTLs, including DNA methylation QTLs (meQTLs), are emerging, but cell-type-specific meQTLs using cells of disease origin have been lacking. Here, we established an meQTL dataset by using primary melanocytes from 106 individuals and identified 1,497,502 significant cis-meQTLs. Multi-QTL colocalization with meQTLs, eQTLs, and mRNA splice-junction QTLs from the same individuals together with imputed methylome-wide and transcriptome-wide association studies identified candidate susceptibility genes at 63% of melanoma GWAS loci. Among the three molecular QTLs, meQTLs were the single largest contributor. To compare melanocyte meQTLs with those from malignant melanomas, we performed meQTL analysis on skin cutaneous melanomas from The Cancer Genome Atlas (n = 444). A substantial proportion of meQTL probes (45.9%) in primary melanocytes is preserved in melanomas, while a smaller fraction of eQTL genes is preserved (12.7%). Integration of melanocyte multi-QTLs and melanoma meQTLs identified candidate susceptibility genes at 72% of melanoma GWAS loci. Beyond GWAS annotation, meQTL-eQTL colocalization in melanocytes suggested that 841 unique genes potentially share a causal variant with a nearby methylation probe in melanocytes. Finally, melanocyte trans-meQTLs identified a hotspot for rs12203592, a cis-eQTL of a transcription factor, IRF4, with 131 candidate target CpGs. Motif enrichment and IRF4 ChIP-seq analysis demonstrated that these target CpGs are enriched in IRF4 binding sites, suggesting an IRF4-mediated regulatory network. Our study highlights the utility of cell-type-specific meQTLs.

Biophysical evidence to support and extend the vitamin D-folate hypothesis as a paradigm for the evolution of human skin pigmentation

OBJECTIVE

To test the "vitamin D-folate hypothesis for the evolution of human skin pigmentation."

METHODS

Total ozone mapping spectrometer (TOMS) satellite data were used to examine surface UV-irradiance in a large (n = 649) Australian cross-sectional study population. Genetic analysis was used to score vitamin D- and folate-related gene polymorphisms (n = 22), along with two pigmentation gene variants (IRF4-rs12203592/HERC2-rs12913832). Red cell folate and vitamin D₃ were measured by immunoassay and HPLC, respectively.

RESULTS

Ultraviolet radiation (UVR) and pigmentation genes interact to modify blood vitamin levels; Light skin IRF4-TT genotype has greatest folate loss while light skin HERC2-GG genotype has greatest vitamin D₃ synthesis (reflected in both TOMS and seasonal data). UV-wavelength exhibits a dose-response relationship in folate loss within light skin IRF4-TT genotype (305 > 310 > 324 > 380 nm). Significant vitamin D₃ photosynthesis only occurs within light skin HERC2-GG genotype, and is maximal at 305 nm. Three dietary antioxidants (vitamins C, E, and β-carotene) interact with UVR and pigmentation genes preventing oxidative loss of labile reduced folate vitamers, with greatest benefit in light skin IRF4-TT subjects. The putative photosensitiser, riboflavin, did not sensitize red cell folate to UVR and actually afforded protection. Four genes (5xSNPs) influenced blood vitamin levels when stratified by pigmentation genotype; MTHFR-rs1801133/rs1801131, TS-rs34489327, CYP24A-rs17216707, and VDR-ApaI-rs7975232. Lightest IRF4-TT/darkest HERC2-AA genotype combination (greatest folate loss/lowest vitamin D₃ synthesis) has 0% occurrence. The opposing, commonest (39%) compound genotype (darkest IRF4-CC/lightest HERC2-GG) permits least folate loss and greatest synthesis of vitamin D₃ .

CONCLUSION

New biophysical evidence supports the vitamin D-folate hypothesis for evolution of skin pigmentation.

Search for genetic loci involved in the constitution and skin type of a Japanese women using a genome-wide association study

The constitution and skin type of individuals are influenced by various factors. Recently, the influence of genetic predispositions on these has been emphasized. To date, genome-wide association studies (GWAS) have shown several single nucleotide polymorphisms (SNPs) that affect individual's constitution and skin type. However, these studies have mainly focused on the Caucasian population, and only a few association analyses with the constitution and skin type of individuals involving a Japanese population have been conducted. In this study, we conducted a GWAS analysis of 9 phenotypes regarding the constitution or skin type of 1108 Japanese women based on a questionnaire. As a result, in addition to SNPs known to be involved in phenotypes in the past, we discovered new SNPs and genetic regions related to darkness of pigmented spots, skin flushing, frequency of rough skin and responsiveness to cosmetics.

Introgression contributes to distribution of structural variations in cattle

Structural variations (SVs) are an important source of phenotypic diversity in cattle. Here, 72 whole genome sequences representing taurine and zebu cattle were used to identify SVs. Applying multiple approaches, 16,738 SVs were identified. A comparison against the Database of Genomic Variants archives revealed that 1575 SVs were novel in our data. A novel duplication covering the entire GALNT15 gene, was observed only in N'Dama. A duplication, which was previously reported only in zebu and associated with navel length, was also observed in N'Dama. Investigation of a novel deletion located upstream of CAST13 gene and identified only in Italian cattle and zebu, revealed its introgressed origin in the former. Overall, our data highlights how the SVs distribution in cattle is also shaped by forces such as demographical differences and gene flow. The cattle SVs of this study and its meta-data can be visualized on an interactive genome browser at https://tinyurl.com/svCowArs.

Prediction of Eye Colour in Scandinavians Using the EyeColour 11 (EC11) SNP Set

Description of a perpetrator's eye colour can be an important investigative lead in a forensic case with no apparent suspects. Herein, we present 11 SNPs (Eye Colour 11-EC11) that are important for eye colour prediction and eye colour prediction models for a two-category reporting system (blue and brown) and a three-category system (blue, intermediate, and brown). The EC11 SNPs were carefully selected from 44 pigmentary variants in seven genes previously found to be associated with eye colours in 757 Europeans (Danes, Swedes, and Italians). Mathematical models using three different reporting systems: a quantitative system (PIE-score), a two-category system (blue and brown), and a three-category system (blue, intermediate, brown) were used to rank the variants. SNPs with a sufficient mean variable importance (above 0.3%) were selected for EC11. Eye colour prediction models using the EC11 SNPs were developed using leave-one-out cross-validation (LOOCV) in an independent data set of 523 Norwegian individuals. Performance of the EC11 models for the two- and three-category system was compared with models based on the IrisPlex SNPs and the most important eye colour locus, rs12913832. We also compared model performances with the IrisPlex online tool (IrisPlex Web). The EC11 eye colour prediction models performed slightly better than the IrisPlex and rs12913832 models in all reporting systems and better than the IrisPlex Web in the three-category system. Three important points to consider prior to the implementation of eye colour prediction in a forensic genetic setting are discussed: (1) the reference population, (2) the SNP set, and (3) the reporting strategy.