Leonie C. Jacobs

Comprehensive candidate gene study highlights UGT1A and BNC2 as new genes determining continuous skin color variation in Europeans

Natural variation in human skin pigmentation is primarily due to genetic causes rooted in recent evolutionary history. Genetic variants associated with human skin pigmentation confer risk of skin cancer and may provide useful information in forensic investigations. Almost all previous gene-mapping studies of human skin pigmentation were based on categorical skin color information known to oversimplify the continuous nature of human skin coloration. We digitally quantified skin color into hue and saturation dimensions for 5,860 Dutch Europeans based on high-resolution skin photographs. We then tested an extensive list of 14,185 single nucleotide polymorphisms in 281 candidate genes potentially involved in human skin pigmentation for association with quantitative skin color phenotypes. Confirmatory association was revealed for several known skin color genes including HERC2, MC1R, IRF4, TYR, OCA2, and ASIP. We identified two new skin color genes: genetic variants in UGT1A were significantly associated with hue and variants in BNC2 were significantly associated with saturation. Overall, digital quantification of human skin color allowed detecting new skin color genes. The variants identified in this study may also contribute to the risk of skin cancer. Our findings are also important for predicting skin color in forensic investigations.

Genetics of skin color variation in Europeans: genome‑wide association studies with functional follow‑up

AbstractIn the International Visible Trait Genetics (VisiGen) Consortium, we investigated the genetics of human skin color by combining a series of genome-wide association studies (GWAS) in a total of 17,262 Europeans with functional follow-up of discovered loci. Our GWAS provide the first genome-wide significant evidence for chromosome 20q11.22 harboring the ASIP gene being explicitly associated with skin color in Europeans. In addition, genomic loci at 5p13.2 (SLC45A2), 6p25.3 (IRF4), 15q13.1 (HERC2/OCA2), and 16q24.3 (MC1R) were confirmed to be involved in skin coloration in Europeans. In follow-up gene expression and regulation studies of 22 genes in 20q11.22, we highlighted two novel genes EIF2S2 and GSS, serving as competing functional candidates in this region and providing future research lines. A genetically inferred skin color score obtained from the 9 top-associated SNPs from 9 genes in 940 worldwide samples (HGDP-CEPH) showed a clear gradual pattern in Western Eurasians similar to the distribution of physical skin color, suggesting the used 9 SNPs as suitable markers for DNA prediction of skin color in Europeans and neighboring populations, relevant in future forensic and anthropological investigations.

A Genome-Wide Association Study Identifies the Skin Color Genes IRF4, MC1R, ASIP, and BNC2 Influencing Facial Pigmented Spots

Facial pigmented spots are a common skin aging feature, but genetic predisposition has yet to be thoroughly investigated. We conducted a genome-wide association study for pigmented spots in 2,844 Dutch Europeans from the Rotterdam Study (mean age: 66.9±8.0 years; 47% male). Using semi-automated image analysis of high-resolution digital facial photographs, facial pigmented spots were quantified as the percentage of affected skin area (mean women: 2.0% ±0.9, men: 0.9% ±0.6). We identified genome-wide significant association with pigmented spots at three genetic loci: IRF4 (rs12203592, P=1.8 × 10(-27)), MC1R (compound heterozygosity score, P=2.3 × 10(-24)), and RALY/ASIP (rs6059655, P=1.9 × 10(-9)). In addition, after adjustment for the other three top-associated loci the BNC2 locus demonstrated significant association (rs62543565, P=2.3 × 10(-8)). The association signals observed at all four loci were successfully replicated (P<0.05) in an independent Dutch cohort (Leiden Longevity Study n=599). Although the four genes have previously been associated with skin color variation and skin cancer risk, all association signals remained highly significant (P<2 × 10(-8)) when conditioning the association analyses on skin color. We conclude that genetic variations in IRF4, MC1R, RALY/ASIP, and BNC2 contribute to the acquired amount of facial pigmented spots during aging, through pathways independent of the basal melanin production.

IRF4, MC1R, and TYR genes are risk factors for actinic keratosis independent of skin color

Actinic keratosis (AK) is a pre-malignant skin disease, highly prevalent in elderly Europeans. This study investigates genetic susceptibility to AK with a genome-wide association study (GWAS). A full body skin examination was performed in 3194 elderly individuals from the Rotterdam Study (RS) of exclusive north-western European origin (aged 51-99 years, 45% male). Physicians graded the number of AK into four severity levels: none (76%), 1-3 (14%), 4-9 (6%) and ≥10 (5%), and skin color was quantified using a spectrophotometer on sun-unexposed skin. A GWAS for AK severity was conducted, where promising signals at IRF4 and MC1R (P < 4.2 × 10(-7)) were successfully replicated in an additional cohort of 623 RS individuals (IRF4, rs12203592, Pcombined = 6.5 × 10(-13) and MC1R, rs139810560, Pcombined = 4.1 × 10(-9)). Further, in an analysis of ten additional well-known human pigmentation genes, TYR also showed significant association with AK (rs1393350, P = 5.3 × 10(-4)) after correction for multiple testing. Interestingly, the strength and significance of above-mentioned associations retained largely the same level after skin color adjustment. Overall, our data strongly suggest that IRF4, MC1R and TYR genes likely have pleiotropic effects, a combination of pigmentation and oncogenic functions, resulting in an increased risk of AK.

Intrinsic and Extrinsic Risk Factors for Sagging Eyelids

IMPORTANCE Sagging eyelids, or dermatochalasis, are a frequent concern in older adults. It is considered a feature of skin aging, but risk factors other than aging are largely unknown. OBJECTIVE To study nongenetic and genetic risk factors for sagging eyelids. DESIGN Upper eyelid sagging was graded in 4 categories of severity using digital photographs. Dermatochalasis was defined as the eyelid hanging over the eyelashes. Age, sex, skin color, tanning ability, hormonal status in women, current smoking, body mass index, and sun protection behavior were analyzed in a multivariable multinomial logistic regression model. Genetic predisposition was assessed using heritability analysis and a genome-wide association study. SETTING AND PARTICIPANTS The study was performed in 2 independent population-based cohorts. The Rotterdam Study included older adults from one district in Rotterdam, the Netherlands, and the UK Adult Twin Registry (TwinsUK) included twins from all over the United Kingdom. Participants were 5578 unrelated Dutch Europeans (mean age, 67.1 years; 44.0% male) from the Rotterdam Study and 2186 twins (mean age, 53.1 years; 10.4% male) from the TwinsUK. MAIN OUTCOMES AND MEASURES Sagging eyelid severity levels, ranging from 1 (normal control) to 4 (severe sagging). RESULTS Among 5578 individuals from the Rotterdam Study, 17.8% showed dermatochalasis (moderate and severe sagging eyelids). Significant and independent risk factors for sagging eyelids included age, male sex, lighter skin color, and higher body mass index. In addition, current smoking was borderline significantly associated. Heritability of sagging eyelids was estimated to be 61% among 1052 twin pairs from the TwinsUK (15.6% showed dermatochalasis). A meta-analysis of genome-wide association study results from 5578 Rotterdam Study and 1053 TwinsUK participants showed a genome-wide significant recessive protective effect of the C allele of rs11876749 (P = 1.7 × 10(-8)). This variant is located close to TGIF1 (an inducer of transforming growth factor β), which is a known gene associated with skin aging. CONCLUSIONS AND RELEVANCE This is the first observational study to date demonstrating that other risk factors (male sex, genetic variants, lighter skin color, high body mass index, and possibly current smoking) in addition to aging are involved in the origin of sagging eyelids.

Validation of image analysis techniques to measure skin aging features from facial photographs

Accurate measurement of the extent skin has aged is crucial for skin aging research. Image analysis offers a quick and consistent approach for quantifying skin aging features from photographs, but is prone to technical bias and requires proper validation.

Determinants for Quantitative Sensory Testing and the Association with Chronic Musculoskeletal Pain in the General Elderly Population

Chronic musculoskeletal pain is accompanied by central sensitization, which can be determined with quantitative sensory testing (QST). In this study, we aim to investigate whether central sensitization, as measured by thermal QST, is detectable in community‐dwelling elderly individuals suffering from self‐reported chronic pain and identify determinants influencing thermal QST measurement analyses and interpretation.

Perceived skin colour seems a swift, valid and reliable measurement

DEAR EDITOR, Skin colour is an important trait in dermatological research because it modifies the risk of many skin diseases. In clinical practice dermatologists evaluate skin colour by a quick visual assessment of the sun-unexposed skin. Because visual assessment might be subjective, Fitzpatrick proposed a sun-sensitivity skin-type (Fitzpatrick skin type, FST) classification as a better alternative to quantify skin colour. However, this self-reported skin type might change in time and could be biased because light-skinned individuals tend to overestimate their skin colour. Alternatively, a spectrophotometer measures skin colour objectively, but might be influenced by the seasonal variations and colour inequalities. Visual assessment of perceived skin colour (PSC) allows physicians to combine different clues besides the colour (such as freckles), and to exclude tanning influences, into one skin-colour category. PSC has been used in several studies, but it has not yet been validated. We investigated the reliability of physicians’ perception of skin colour, and how PSC relates to the widely used FST and to unexposed skin colour quantified by a spectrophotometer. This study included adult volunteers visiting the dermatology department of Erasmus MC Rotterdam, the Netherlands, in December 2014 (exclusion criteria: albinism and erythroderma). A sample-size calculation showed 80% power to detect an inter-rater correlation of 0 8 with a maximum deviation of 0 1 when 80 participants were included. The local medical ethics committee approved this study and all participants signed informed consent. Skin colour was assessed using a six-point scale: 1 very white, 2 white, 3 white to olive, 4 light brown, 5 brown and 6 dark brown to black. Three physicians (L.C.J., M.A.H. and J.A.C.V.) independently graded the colour of sun-unexposed skin of the upper body (abdomen and inner upper arm) of each participant, without discussing their assessments. The agreement in grading was tested using the intraclass correlation coefficient (ICC; two-way-mixed, single measures). Subsequently, skin colour was measured as colour saturation at the inner upper arm using a spectrophotometer (CM-600d; Konica-Minolta, Osaka, Japan), and the FST was assessed by combining the answers to the questions: ‘What is your skin colour?’ (type I–IV white, type V brown, type VI black) and, ‘If white, how does your unprotected skin react to sunlight?’ (type I always burns and never tans, type II usually burns and afterwards lightly tans, type III sometimes burns and always tans, type IV never burns and tans deeply). Spearman’s q was used to test the correlation of the spectrophotometer skin colour with PSC and FST. We studied 117 individuals (mean age 45 7 18 6 years, 31% men) of different ancestry. The mean PSC of the three graders included 28 individuals (24%) as very white, 58 (50%) white, 14 (12%) white to olive, six (5%) light brown, 11 (9%) brown and none dark brown to black. The three physicians showed an excellent agreement in grading (ICCabsolute agreement = 0 90). In 114 individuals (three answered ‘unknown’) the self-reported FST included 14 individuals (12%) of type I, 46 (40%) type II, 28 (25%) type III, four (4%) type IV, 22 (19%) type V and none type VI. Colour saturation of unexposed skin ranged from 0 17 (very white) to 0 45 (dark) and was highly correlated with mean PSC (q = 0 82, Fig. 1a, and less so with FST (q = 0 63, Fig. 1b). The FST was generally higher than the mean PSC (mean difference = 0 5, P < 0 001; Fig. 2), but consistency between PSC and FST was still high (ICCconsistency = 0 82). Five individuals were white or white to olive according to the physicians but judged themselves as brown. However, none of the individuals with light brown or brown PSC judged their own skin as white (Fig. 2). After excluding these five individuals, the consistency between PSC and FST increased to an ICC of 0 86. Comparing PSC in younger (≤ 45 years, n = 60) vs. older (> 45 years, n = 57) individuals, a similar agreement between the three physicians was seen (ICCabsolute agreement young = 0 89, ICC old = 0 90). However, the correlation between the mean PSC and the FST was higher in the younger individuals (ICCconsistency young = 0 89, ICC old = 0 76). To assess differences in sun reaction between the present and the teenage years, we asked the volunteers whether their answers to the FST questions would have been different for their teens. Seven individuals reported a higher FST in the past and 11 a lower FST. Most individuals with a higher FST in the past were aged < 45 years (six of seven), and most individuals with a lower FST in the past would have had an FST of I in their teens (seven of 11). Our results show that physician assessment of skin colour is reliable, because minimal interobserver variability was observed. The self-reported FST is higher than the PSC, but largely consistent with it. However, the spectrophotometer colour saturation correlated less with the FST than with the PSC. This suggests that PSC is a mix between true colour (spectrophotometer) and sun sensitivity (FST). Moreover, our data confirm that light-skinned individuals tend to overestimate

Novel pleiotropic risk loci for melanoma and nevus density implicate multiple biological pathways

The total number of acquired melanocytic nevi on the skin is strongly correlated with melanoma risk. Here we report a meta-analysis of 11 nevus GWAS from Australia, Netherlands, United Kingdom, and United States, comprising a total of 52,506 phenotyped individuals. We confirm known loci including MTAP, PLA2G6, and IRF4, and detect novel SNPs at a genome-wide level of significance in KITLG, DOCK8, and a broad region of 9q32. In a bivariate analysis combining the nevus results with those from a recent melanoma GWAS meta-analysis (12,874 cases, 23,203 controls), SNPs near GPRC5A, CYP1B1, PPARGC1B, HDAC4, FAM208B and SYNE2 reached global significance, and other loci, including MIR146A and OBFC1, reached a suggestive level of significance. Overall, we conclude that most nevus genes affect melanoma risk (KITLG an exception), while many melanoma risk loci do not alter nevus count. For example, variants in TERC and OBFC1 affect both traits, but other telomere length maintenance genes seem to affect melanoma risk only. Our findings implicate multiple pathways in nevogenesis via genes we can show to be expressed under control of the MITF melanocytic cell lineage regulator.

A healthy diet in women is associated with less facial wrinkles in a large Dutch population-based cohort

Background: Little is known about the effects of different dietary patterns on facial wrinkling. Objective: We aimed to investigate the association between diet and facial wrinkles in a population‐based cohort of 2753 elderly participants of the Rotterdam study. Methods: Wrinkles were measured in facial photographs by digitally quantifying the area wrinkles occupied as a percentage of total skin area. Diet was assessed by the Food Frequency Questionnaire. Adherence to the Dutch Healthy Diet Index (DHDI) was calculated. In addition, we used principal component analysis (PCA) to extract relevant food patterns in men and women separately. All food patterns and the DHDI were analyzed for an association with wrinkle severity using multivariable linear regression. Results: Better adherence to the Dutch guidelines was significantly associated with less wrinkles among women but not in men. In women, a red meat and snack–dominant PCA pattern was associated with more facial wrinkles, whereas a fruit‐dominant PCA pattern was associated with fewer wrinkles. Limitations: Due to the cross‐sectional design of our study, causation could not be proven. Other health‐conscious behaviors of study participants could have influenced the results. Conclusion: Dietary habits are associated with facial wrinkling in women. Global disease prevention strategies might benefit from emphasizing that a healthy diet is also linked to less facial wrinkling.