The interplay of sun damage and genetic risk in Australian multiple and single primary melanoma cases and controls

BACKGROUND

Skin phenotype, host genotype and ultraviolet (UV) damage play a role in the development of melanoma.

OBJECTIVES

To ascertain whether the level of UV damage at the site of melanomas was associated with genetic polymorphisms.

METHODS

Deep phenotyping was performed on 1244 individuals; 281 with multiple primary melanomas (MPMs), 304 with single primary melanoma (SPM) and 659 convenience controls. Genotype data was generated using the Illumina CoreExome microarray platform, assaying over 500 000 single-nucleotide polymorphisms. A subset of variants were combined to assess a polygenic risk score (PRS) for melanoma.

RESULTS

Most MPM cases were diagnosed in patients aged > 40 years, in sites with visible chronic UV damage. Women and those diagnosed at age ≤ 40 years were less likely to have perilesional UV damage. Patients with MPM had higher frequencies of MITF E318K, MC1R R-alleles and the ASIP risk haplotype. Individuals who had melanoma in a visibly UV-damaged site were more likely to carry MC1R rs75570604 [odds ratio (OR) 2·5], 9q31.2 rs10816595 (OR 1·4) and MTAP rs869329 (OR 1·4). These same alleles were more common in patients with MPM who were diagnosed at age ≤ 40 years. The mean PRS was significantly higher in MPM than in SPM and controls. Naevus count was comparable in early-onset MPM cases and those diagnosed at age > 40 years.

CONCLUSIONS

Our cohort demonstrated higher frequencies of previously reported alleles associated with melanoma. MPM melanomas more commonly occur in UV-damaged areas, and these individuals are more likely to carry MC1R red hair colour alleles. Awareness of the interplay of genetic vulnerability with UV damage can stratify risk and guide recommendations for melanoma screening. What's already known about this topic? Skin phenotype, host genotype and ultraviolet (UV) damage all play a role in melanoma development. One of the main risk factors is a personal history of melanoma; second and subsequent primary melanomas account for over 20% of all melanomas registered in Queensland. Multiple loci are associated with melanoma risk, including many low-penetrance loci, which may have a cumulatively significant risk. Population-wide screening programmes for melanoma are not yet economically viable. What does this study add? Patients diagnosed with melanoma at age ≤ 40 years were more likely than older patients to have melanomas in non-UV-damaged sites. Patients with multiple melanomas had higher frequencies of MITF E318K, MC1R R-alleles, and the ASIP extended risk haplotype than patients with single melanoma. CDKN2A, MC1R and MTAP variants were more frequent in patients who developed melanomas at a younger age, but also in those whose melanomas were all on visibly UV-damaged sites. What is the translational message? Incorporating these genetic findings into the known risk factors of skin phenotype and visible UV damage may allow for a more customized and economically feasible approach to early detection of melanoma, particularly in younger patients. Plain language summary available online.

Phenotypic and genotypic analysis of amelanotic and hypomelanotic melanoma patients

BACKGROUND

Amelanotic/hypomelanotic melanoma is associated with poorer outcomes due to a more advanced disease stage at diagnosis.

OBJECTIVE

To determine phenotypic risks and genotypic associations with amelanotic/hypomelanotic melanoma to develop a clinical and genetic profile that could assist in identifying high-risk individuals.

METHODS

The Brisbane Naevus Morphology Study conducted from 2009 to 2016 has recruited a core of 1254 participants. Participants were drawn from a combination of volunteers from dermatology outpatient clinics, private dermatology clinics, the Brisbane Longitudinal Twin Study and QSkin study. Case participants had a personal history of melanoma and control participants no personal history of melanoma. We specifically examined seven known candidate pigmentation and melanoma genes and pigmentary phenotypic characteristics in participants with amelanotic/hypomelanotic melanoma compared to pigmented melanomas. This assayed single nucleotide polymorphisms in MC1R, TYR, HERC/OCA2, IRF4, MTAP, PLA2G6 and MITF.

RESULTS

Forty-seven participants had at least one amelanotic/hypomelanotic melanoma, and 389 had pigmented melanomas, with amelanotic/hypomelanotic melanoma patients significantly older than pigmented melanoma participants (63.3 ± 13.0 vs. 54.6 ± 15.3 years; P < 0.001). Amelanotic/hypomelanotic melanoma patients were more likely than pigmented melanoma patients to have red hair (34% vs. 15%; P = 0.01), severe hand freckling (13% vs. 5%; P = 0.01) and propensity to sunburn (63% vs. 44%; P = 0.01). MC1R R/R genotype was much more frequent in our amelanotic/hypomelanotic melanoma population (31.1% vs. 11%; P < 0.001; OR 26.4 vs. 5.9; control 1.0). Amelanotic/hypomelanotic melanoma was associated with TYR rs1126809*A/A [OR (CI 95%) 2.7 (1.1-6.8) vs. 1.2 (0.8-1.9)] and PLA2G6 rs11570734*A/A [OR (CI 95%) 3.7 (1.0-13.6) vs. 1.3 (0.9-2.0)]. The MTAP melanoma risk SNP genotype, associated with darker pigmentation, (rs4636294*A/A) was less common in amelanotic/hypomelanotic melanoma patients [OR (CI 95%) 0.8 (0.3-2.1) vs. 2.0 (1.3-3.1)].

CONCLUSIONS

Knowledge of phenotypic and genotypic associations of amelanotic/hypomelanotic melanoma can help predict risks and associations of this difficult to diagnose melanoma, which may ultimately assist clinical management and patient skin self-examination.

Iris pigmented lesions as a marker of cutaneous melanoma risk: an Australian case-control study

BACKGROUND

Iris naevi and iris freckles have a frequency of 4% and 50% in the European population, respectively. They are associated with dysplastic naevi, but few studies have examined their link to cutaneous melanoma.

OBJECTIVES

To assess whether iris pigmented lesions are a predictive indicator for cutaneous melanoma.

METHODS

This is a melanoma case-control study of 1254 European-background Australians. Sun exposure and melanoma history, a saliva sample for DNA analysis and eye photographs taken with a digital camera were collected from 1117 participants. Iris images were assessed by up to four trained observers for the number of iris pigmented lesions. The data were analysed for correlations between iris pigmented lesions and melanoma history.

RESULTS

Case participants over the age of 40 had similar numbers of iris pigmented lesions to age matched controls (mean 5·7 vs. 5·2, P = 0·02), but in younger case and control participants there was a greater difference (mean 3·96 vs. 2·19, P = 0·004). A logistic regression adjusted for age, sex, skin, hair and eye colour, skin freckling and naevus count found that the presence of three or more iris pigmented lesions increases the melanoma risk 1·45-fold [95% confidence interval (CI) 1·07-1·95]. HERC2/OCA2 rs12913832 and IRF4 rs12203592 influenced both eye colour and the number of iris pigmented lesions. On the HERC2/OCA2 A/A and A/G genotype background there was an increasing proportion of blue eye colour when carrying the IRF4 T allele (P = 3 × 10^-4 ) and a higher number of iris pigmented lesions with the IRF4 T/T homozygote (P = 3 × 10^-9 ).

CONCLUSIONS

Iris pigmented lesion count provides additional predictive information for melanoma risk above that from conventional risk factors.

Heritability of naevus patterns in an adult twin cohort from the Brisbane Twin Registry: a cross-sectional study

BACKGROUND

Heritability of naevi counts is widely acknowledged as a potential surveillance parameter for prevention purposes. The contribution of heritability to the changes seen in naevus number and morphology over time and their corresponding dermoscopic characteristics is unknown, but is important to understand in order to account for adequate prevention measures.

OBJECTIVES

To identify naevus characteristics that are strongly influenced by heritability.

METHODS

This cross-sectional study included 220 individuals [76 monozygotic (MZ), 144 dizygotic (DZ)], recruited from the Brisbane Twin Naevus Study. Participants received full body imaging and dermoscopy of naevi ≥ 5 mm in diameter. Dermoscopic type, total naevus count (TNC), change in TNC with age, and naevus distribution, size, colour and profile were compared between MZ and DZ twins. Heritability of these traits was assessed via Falconer's estimate.

RESULTS

Significant differences were found in comparing MZ and DZ twins for TNC, numbers of naevi 5·0-7·9 mm in diameter, counts of light-brown naevi, naevi on the back and sun-protected sites, and naevi with the 'nonspecific' dermoscopic pattern.

CONCLUSIONS

This study strongly supports a heritable component to TNC, as well as changes in TNC, and the number of medium-sized naevi, light-brown naevi, specific sites and certain dermoscopic features in adults. These characteristics should be taken into account by naevus surveillance programmes and further studied to identify candidate gene associations for clinical and dermoscopic patterns in conjunction with melanoma risk stratification.

Genetic Factors Explain Variation in the Age at Onset of Psoriasis: A Population-based Twin Study

The aim of this study was to determine the age at onset of psoriasis in a population-based twin sample. Questionnaire-data in 10,725 twin pairs, 20-71 years of age, from the Danish Twin Registry, was collected, and analysed using survival regression analysis. Median age at onset was 25 and 28 years among women and men, respectively. The correlation between the ages was 0.84 (bootstrap standard error?=?0.044) in monozygotic twin pairs and 0.60 (0.051) in dizygotic twin pairs, permutation p?=?0.001. Age at onset of psoriasis in the index twin did not predict risk of psoriasis in the co-twin, hazard ratio (per year of later onset =?1.01 (0.99-1.03), p?=?0.434. In conclusion, these data support that the age at onset of psoriasis is, in part, an inherited property. Our results do not support that early-onset psoriasis is more genetically determined.

The inheritance of extra-hepatic portosystemic shunts and elevated bile acid concentrations in Maltese dogs

OBJECTIVES

To determine the heritability of extra-hepatic portosystemic shunts and elevated post-prandial serum bile acid concentrations in Maltese dogs.

MATERIALS AND METHODS

Maltese dogs were recruited and investigated by a variable combination of procedures including dynamic bile acid testing, rectal ammonia tolerance testing, ultrasonography, portal venography, surgical inspection or necropsy. In addition, nine test matings were carried out between affected and affected dogs, and affected and unaffected dogs.

RESULTS

In 135 variably related Maltese, shunt status could be confirmed in 113, including 19 with an extra-hepatic portosystemic shunt (17 confirmed at surgery, 2 at necropsy). Rectal ammonia tolerance testing results and post-prandial serum bile acid concentrations were retrievable for 50 and 88 dogs, respectively. Pedigree information was available for these 135 and an additional 164 related dogs. Two consecutive test matings were carried out between two affected animals (whose shunts had been attenuated), with 2 of 8 (25%) of offspring having an extra-hepatic portosystemic shunt. Six test matings were carried out between an affected and an unaffected animal, with 2 of 22 (9%) offspring affected. Heritability of extra-hepatic portosystemic shunt was 0·61 calculated using variance components analysis [95% confidence interval (CI) 0·14 to 1·0, P=0·001]. The best fitting model from segregation analysis was a common, partially penetrant, recessive model (allele frequency 0·34, penetrance 0·99, CI 0·09 to 1·0). The heritability of elevated post-prandial serum bile acid (and thus likely portal vein hypoplasia) was 0·81 (CI 0·43 to 1·0, P=0·2) after logarithmic transformation of post-prandial serum bile acid concentrations.

CLINICAL SIGNIFICANCE

There is strong support for extra-hepatic portosystemic shunts and elevated post-prandial serum bile acid concentrations both being inherited conditions in Maltese.

IgE responsiveness to Dermatophagoides farinae in West Highland white terrier dogs is associated with region on CFA35

Immunoglobulin E (IgE)-mediated hypersensitivity against environmental allergens, commonly including Dermatophagoides farinae, is associated with atopic diseases in both humans and dogs. We have recently identified a family of clinically healthy West Highland white terriers (WHWTs) with high-serum D. farinae-IgE levels. In this study, we investigated the genetic mechanism controlling IgE responsiveness in dogs by performing a genome-wide association study (GWAS) using the Affymetrix V2 Dog SNP array in 31 high-IgE and 24 low-IgE responder WHWTs. A gene-dropping simulation method, using SIB-PAIR software, showed significant allelic association between serum D. farinae-specific IgE levels and a 2.3-Mb area on CFA35 (best empirical P = 1 × 10(-5)). A nearby candidate gene, CD83, encodes a protein which has important immunological functions in antigen presentation and regulation of humoral immune responses. We sequenced this gene in 2 high-IgE responders and 2 low-IgE responders and identified an intronic polymorphic repeat sequence with a predicted functional effect, but the association was insufficient to explain the GWAS association signal in this population (P = 1 × 10(-3)). Further studies are necessary to investigate the significance of these findings for IgE responsiveness and atopic disease in the dog.

Relationship between type 1 diabetes and atopic diseases in a twin population

AIM

To study the association between type 1 diabetes and atopic diseases in a twin population.

METHODS

We performed record linkage between questionnaire-defined atopic dermatitis, asthma and hay fever, and hospital discharge diagnoses of type 1 diabetes in 54,530 Danish twins, 3-71 years of age.

RESULTS

The age- and sex-adjusted risk of atopic dermatitis was decreased in subjects with type 1 diabetes compared with nondiabetic subjects, (2.1%vs 9.9%), odds ratio (OR)= 0.23 (0.07-0.71), P = 0.011, whereas asthma and hay fever were not significantly associated with type 1 diabetes. Within twin pairs discordant for type 1 diabetes, the diabetic twin had a lower risk of atopic dermatitis relative to the nondiabetic co-twin. Genetic factors for atopic dermatitis and type 1 diabetes were negatively correlated (r = -0.30), P = 0.0009.

CONCLUSIONS

These findings substantiate the Th1 vs Th2 cell dichotomy for type 1 diabetes and atopic dermatitis, and indicate an inverse association between genetic factors for these disorders.

Risk of asthma in adult twins with type 2 diabetes and increased body mass index

AIM

To examine the relationship between asthma, type 2 diabetes and increased body mass index (BMI) in adult twins.

METHODS

We performed record linkage between questionnaire-defined asthma and BMI, and hospital discharge diagnoses of type 2 diabetes in 34,782 Danish twins, 20-71 years of age.

RESULTS

The risk of asthma was increased in subjects with type 2 diabetes relative to nondiabetic subjects both in men (13.5%vs 7.5%), P = 0.001 and in women (16.6%vs 9.6%), P = 0.001. The result remained significant after adjustment for age, BMI, smoking, symptoms of chronic bronchitis, marital status and zygosity, men: OR = 1.70 (1.07-2.70), P = 0.026; women: OR = 1.88 (1.24-2.85), P = 0.003. In this analysis, BMI remained a highly significant predictor for asthma independently of diabetes status in women, P < 0.000 but not in men, P = 0.336. Significant positive genetic correlations were found between asthma and type 2 diabetes, 0.20 (0.01-0.40), P = 0.047; between asthma and BMI in women, 0.15 (0.07-0.22), P < 0.000; and between BMI and type 2 diabetes, 0.40 (0.29-0.43), P < 0.000.

CONCLUSIONS

Asthma, type 2 diabetes and increased BMI are strongly associated in adults, particularly in women. These results suggest a common aetiology for asthma and metabolic syndrome.

Characterization of the methylation patterns of MS4A2 in atopic cases and controls

BACKGROUND

It is largely unknown whether epigenetic modifications of key genes may contribute to the reported maternal effects in atopy. The aim of this study was to characterize the methylation patterns of the membrane-spanning 4-domains, subfamily A, member 2 gene (MS4A2) (beta-chain of the IgE high-affinity receptor), a key gene in the allergic cascade.

METHODS

Mass spectrometry and bisulphite sequencing were used to measure the methylation of two potential substrates for epigenetic regulation of MS4A2, namely a predicted promoter and a CpG-rich AluSp repeat. Methylation was measured in DNA extracted from peripheral blood lymphocytes of 38 atopic cases and 37 controls. Cases were positive for atopy, asthma, bronchial hyper-responsiveness and had high IgE levels. Both parents of eight atopic cases were also tested.

RESULTS

The AluSp element was highly methylated across all individuals (mean 0.92, range 0.87-0.94), a pattern inconsistent with classical imprinting. Variation in methylation at this locus was not associated with age, sex, daily steroid use or atopic status, and there were no differences in methylation between mothers and fathers of atopic cases. Bisulphite sequencing analysis of the promoter region showed that it was also not imprinted, and there was no evidence for allele-specific methylation, but we were unable to test for association with atopy status.

CONCLUSIONS

Methylation levels at the AluSp repeat analysed in MS4A2 were inconsistent with classical imprinting mechanisms and did not associate with atopy status. The promoter region was less methylated but further analysis of this region in larger cohorts is warranted to investigate its role in allergic disease.

Association and interaction analyses of eight genes under asthma linkage peaks

BACKGROUND

Linkage studies have implicated the 2q33, 9p21, 11q13 and 20q13 regions in the regulation of allergic disease. The aim of this study was to test genetic variants in candidate genes from these regions for association with specific asthma traits.

METHODS

Ninety-five single nucleotide polymorphisms (SNP) located in eight genes (CD28, CTLA4, ICOS, ADAM23, ADAMTSL1, MS4A2, CDH26 and HRH3) were genotyped in >5000 individuals from Australian (n = 1162), Dutch (n = 99) and Danish (n = 303) families. Traits tested included doctor-diagnosed asthma, atopy, airway obstruction, total serum immunoglobulin (Ig) E levels and eosinophilia. Association was tested using both multivariate and univariate methods, with gene-wide thresholds for significance determined through simulation. Gene-by-gene and gene-by-environment analyses were also performed.

RESULTS

There was no overall evidence for association with seven of the eight genes tested when considering all genetic variation assayed in each gene. The exception was MS4A2 on chromosome 11q13, which showed weak evidence for association with IgE (gene-wide P < 0.05, rs502581). There were no significant gene-by-gene or gene-by-environment interaction effects after accounting for the number of tests performed.

CONCLUSIONS

The individual variants genotyped in the 2q33, 9p21 and 20q13 regions do not explain a large fraction of the variation in the quantitative traits tested or have a major impact on asthma or atopy risk. Our results are consistent with a weak effect of MS4A2 polymorphisms on the variation of total IgE levels.

Family-based mitochondrial association study of traits related to type 2 diabetes and the metabolic syndrome in adolescents

AIMS/HYPOTHESIS

There has been much focus on the potential role of mitochondria in the aetiology of type 2 diabetes and the metabolic syndrome, and many case-control mitochondrial association studies have been undertaken for these conditions. We tested for a potential association between common mitochondrial variants and a number of quantitative traits related to type 2 diabetes in a large sample of >2,000 healthy Australian adolescent twins and their siblings, many of whom were measured on more than one occasion.

METHODS

To the best of our knowledge, this is the first mitochondrial association study of quantitative traits undertaken using family data. The maternal inheritance pattern of mitochondria means established association methodologies are unsuitable for analysis of mitochondrial data in families. We present a methodology, implemented in the freely available program Sib-Pair for performing such an analysis.

RESULTS

Despite our study having the power to detect variants with modest effects on these phenotypes, only one significant association was found after correction for multiple testing in any of four age groups. This was for mt14365 with triacylglycerol levels (unadjusted p = 0.0006). This association was not replicated in other age groups.

CONCLUSIONS/INTERPRETATION

We find little evidence in our sample to suggest that common European mitochondrial variants contribute to variation in quantitative phenotypes related to diabetes. Only one variant showed a significant association in our sample, and this association will need to be replicated in a larger cohort. Such replication studies or future meta-analyses may reveal more subtle effects that could not be detected here because of limitations of sample size.

Cyclooxygenase-2 gene polymorphisms in an Australian population: association of the -1195G > A promoter polymorphism with mild asthma

BACKGROUND

Cyclooxygenase (COX)-2 is an inducible enzyme responsible for catalysing the formation of prostaglandins (PGs) in settings of inflammation. Single nucleotide polymorphisms (SNPs) of the COX-2 gene may influence gene transcription and PG production in the asthmatic airway.

OBJECTIVE

To evaluate the frequencies of COX-2 SNPs in an Australian Caucasian population, and determine potential associations between common COX-2 promoter SNPs and asthma, asthma severity and aspirin-intolerant asthma (AIA).

METHODS

The frequencies of 25 COX-2 SNPs were determined in a random population (n=176). The SNPs with a minor allele frequency of >10% were then studied in asthmatic (n=663), non-asthmatic controls (n=513) and AIA subjects (n=58). Genotype, allele and haplotype associations were assessed. Functional assessment of SNPs was performed by transfection into HeLa cells measured using the luciferase dual-reporter assay system.

RESULTS

Eighteen COX-2 SNPs were not detected, five were rare and two promoter SNPs, -1195G>A (rs689465), and -1290A>G (rs689466), were further studied. The A allele of the -1195 SNP was present at a significantly higher frequency among all asthmatic subjects (P=0.012). Over 60% of the asthmatic individuals were -1195A homozygotes compared with 54.6% of the control subjects (odds ratio, 1.35; 95% CI, 1.06-1.72, P=0.03). After classifying for severity, the mild asthmatics represented 64.6% of -1195AA individuals, the highest of all the asthma groups compared with 54.6% of the control subjects (odds ratio, 1.5; 95% CI, 1.12-2.02, P=0.02). The -1290A/-1195G/-765G haplotype was associated with a reduced incidence of asthma (odds ratio, 0.76; 95% CI, 0.61-0.95, P=0.017).

CONCLUSION

The -1195G>A polymorphism appears to be associated with asthma, and in particular with mild asthma.

Effect of the BDNF V166M polymorphism on working memory in healthy adolescents

Brain-derived neurotrophic factor (BDNF) may play a role in modulating memory function and there is growing evidence that the BDNF V166M polymorphism may influence episodic memory in humans. However, previous association studies examining this polymorphism and working memory are inconsistent. The current study examined this association in a large sample of adolescent twin-pairs and siblings (785 individuals from 439 families). A range of measures (event-related potential, general performance and reaction time) was obtained from a delayed-response working-memory task and total association was examined using the quantitative transmission disequilibrium tests (QTDT) program. Analyses had approximately 93-97% power (alpha= 0.05) to detect an association accounting for as little as 2% of the variance in the phenotypes examined. Results indicated that the BDNF V166M polymorphism is not associated with variation in working memory in healthy adolescents.

Effects of SCA1, MJD, and DPRLA triplet repeat polymorphisms on cognitive phenotypes in a normal population of adolescent twins

The expansion of unstable trinucleotide CAG repeat polymorphisms of a number of genes causes several neurodegenerative disorders with decreased cognitive function, the severity of the disorder being related to allele length at the triplet repeat locus. While the effects of repeat length have been well studied in clinical samples, there has been little investigation of the effects of triplet repeat variation in the normal range for these genes. We have, therefore, examined linkage and association for three CAG triplet repeat markers (Spinocerebellar Ataxia Type 1, SCA1; Machado-Joseph Disease, MJD; Dentatorubro-pallidoluysian Atrophy, DRPLA) to assess their contribution to variation in cognitive ability (IQ, reading ability, processing speed) in a normal, unselected sample of adolescent twins (248 dizygotic (DZ) sibling pairs, aged 16 years). Association tests, performed in Mx and QTDT, showed a consistent positive association of SCA1 with Arithmetic (P = 0.04). While association was supported between SCA1 and Cambridge reading scores and between DRPLA and inspection time, results were inconsistent across software packages. Given the number of statistical tests performed, it is unlikely that trinucleotide repeat variation in the normal range for these genes influences variation in normal cognition.

Genomewide scans of red cell indices suggest linkage on chromosome 6q23

BACKGROUND

The red cell indices quantify the size, number and oxygen-carrying ability of erythrocytes. Although the genetic basis of many monogenic forms of anaemia is well understood, comparatively little is known about the genes responsible for variation in the red cell indices among healthy participants.

OBJECTIVE

To identify quantitative trait loci (QTLs) responsible for normal variation in the red cell indices of 391 pairs of dizygotic twins who were measured longitudinally at 12, 14 and 16 years of age.

RESULTS

Evidence suggesting linkage of red cell indices to haemoglobin concentration (LOD = 3.03) and haematocrit (LOD = 2.95) on chromosome 6q23, a region previously identified as possibly harbouring a QTL for haematocrit, was found. Evidence for linkage to several other regions of the genome, including chromosome 4q32 for red cell count and 7q for mean cell volume, was also found. In contrast, there was little evidence of linkage to the chromosomal regions containing the genes for erythropoietin (7q21) and its receptor (19p13.2), nor to the regions containing the genes for the haemoglobin alpha (16p13.3) and beta chains (11p15.5).

CONCLUSION

Findings provide additional evidence for a QTL affecting haemoglobin and haematocrit on chromosome 6q23. In contrast, polymorphisms in the genes coding for erythropoietin, its receptor and the haemoglobin alpha and beta chains do not appear to contribute substantially to variation in the red cell indices between healthy persons.

Cyclooxygenase-1 gene polymorphisms in patients with different asthma phenotypes and atopy

Cyclooxygenase-1 (COX-1) regulates the biosynthesis of prostaglandins, which are important mediators in asthma. The possible association of COX-1 gene polymorphisms with asthma has not been investigated. The allele frequencies of 20 COX-1 polymorphisms were determined in a random Australian Caucasian population using MassARRAY technology. Informative and potentially functional promoter (c.8592C > T, c.1676C > T) and coding region (c.22C > T, c.50C > T) polymorphisms were investigated in carefully phenotyped patients with mild (n = 316), moderate (n = 241), severe (n = 86) or aspirin-intolerant asthma (AIA) (n = 58), and in nonasthmatic subjects (n = 477). There were no allelic, genotypic or haplotypic associations between these four polymorphisms and asthma or asthma severity. Over-representation of the c.50TT genotype among AIA patients (3.4%) compared with aspirin-tolerant patients (0.8%), and a global haplotype association with AIA did not reach statistical significance. The c.22TT genotype was less frequent among atopic (0.1%) rather than nonatopic individuals (1.2%; odds ratio = 9.05, 95% confidence interval 1.01-81.29). In conclusion, the present investigation of cyclooxygenase-1 polymorphisms in asthma indicates that they do not appear to play a substantial role in genetic pre-disposition for asthma or asthma severity. However, the c.22TT genotype confers a small protective effect against atopy. Potential associations with aspirin-intolerant asthma were identified and warrant further investigation in a larger population of aspirin-intolerant asthma patients.

Increased DNA methylation at the AXIN1 gene in a monozygotic twin from a pair discordant for a caudal duplication anomaly

The AXIN1 gene has been implicated in caudal duplication anomalies. Its coding region was sequenced in both members of a monozygotic (MZ) twin pair discordant for a caudal duplication anomaly, but no mutation was found. Using bisulfite sequencing, we examined methylation at the promoter region of the AXIN1 gene in these twins and in twin and age-matched singleton controls. Methylation of the promoter region in peripheral blood mononucleated cells was variable among individuals, including MZ pairs. In the MZ pair discordant for the caudal duplication, this region of the affected twin was significantly more methylated than that of the unaffected twin (P < .0001), which was significantly more methylated than those of the controls (P = .02). We have confirmed that this CpG island does function as a promoter in vitro and that its activity is inversely proportional to the extent of methylation. This finding raises the possibility that hypermethylation of the AXIN1 promoter, by mechanisms as yet undetermined, is associated with the malformation. This case may be paradigmatic for some cases of MZ discordance.

Risk factors for asthma in young adults: a co-twin control study

BACKGROUND

The liability to asthma is influenced both by genetic and environmental factors. The objective of this study was to identify risk factors for asthma in young adult twin pairs during an 8-year period.

METHODS

From the birth cohorts 1953-1982 of the Danish Twin Registry, 6,090 twin pairs who were initially unaffected with respect to asthma at a nationwide questionnaire-based study in 1994 participated in a similar follow-up study in 2002. Subjects were regarded incident asthma cases when responding affirmatively to the question 'Do you have, or have you ever had asthma'? in 2002. Pairs in which only one twin developed asthma -- discordant pairs -- were identified and conditional logistic regression was applied to detect effects of risk factors.

RESULTS

A total of 126 monozygotic (MZ) and 273 dizygotic (DZ) discordant twin pairs were identified. In MZ twins hay fever (OR = 3.16, 95% CI: 1.29-7.73, P = 0.007) and exercise (OR for inactivity = 0.35, 95% CI: 0.13-0.91, P = 0.023) were significantly associated with asthma, whereas in DZ twins, hay fever (OR = 2.44, 95% CI: 1.44-4.13, P = 0.001), eczema (OR = 1.96, 95% CI: 1.02-3.78, P = 0.040), female sex (OR between males and females = 0.54, 95% CI: 0.36-0.80, P = 0.002), and increasing levels of body mass index (BMI; OR per unit = 1.11, 95% CI: 1.02-1.20, P = 0.009) were significant predictors of asthma.

CONCLUSIONS

Hay fever, eczema, female sex, exercise and increasing levels of BMI were risk factors for asthma in young adults. The different risk profile observed in MZ twins compared with DZ twins may reflect an underlying genetic vulnerability shared between those risk factors and asthma.

Variance components analyses of multiple asthma traits in a large sample of Australian families ascertained through a twin proband

BACKGROUND

Intermediate phenotypes are often measured as a proxy for asthma. It is largely unclear to what extent the same set of environmental or genetic factors regulate these traits.

OBJECTIVE

Estimate the environmental and genetic correlations between self-reported and clinical asthma traits.

METHODS

A total of 3,073 subjects from 802 families were ascertained through a twin proband. Traits measured included self-reported asthma, airway histamine responsiveness (AHR), skin prick response to common allergens including house dust mite (Dermatophagoides pteronyssinus [D. pter]), baseline lung function, total serum immunoglobulin E (IgE) and eosinophilia. Bivariate and multivariate analyses of eight traits were performed with adjustment for ascertainment and significant covariates.

RESULTS

Overall 2,716 participants completed an asthma questionnaire and 2,087 were clinically tested, including 1,289 self-reported asthmatics (92% previously diagnosed by a doctor). Asthma, AHR, markers of allergic sensitization and eosinophilia had significant environmental correlations with each other (range: 0.23-0.89). Baseline forced expiratory volume in 1 s (FEV(1)) showed low environmental correlations with most traits. Fewer genetic correlations were significantly different from zero. Phenotypes with greatest genetic similarity were asthma and atopy (0.46), IgE and eosinophilia (0.44), AHR and D. pter (0.43) and AHR and airway obstruction (-0.43). Traits with greatest genetic dissimilarity were FEV(1) and atopy (0.05), airway obstruction and IgE (0.07) and FEV(1) and D. pter (0.11).

CONCLUSION

These results suggest that the same set of environmental factors regulates the variation of many asthma traits. In addition, although most traits are regulated to great extent by specific genetic factors, there is still some degree of genetic overlap that could be exploited by multivariate linkage approaches.

Genetic time-series analysis identifies a major QTL for in vivo alcohol metabolism not predicted by in vitro studies of structural protein polymorphism at the ADH1B or ADH1C loci

After ingestion of a standardized dose of ethanol, alcohol concentrations were assessed, over 3.5 hours from blood (six readings) and breath (10 readings) in a sample of 412 MZ and DZ twins who took part in an Alcohol Challenge Twin Study (ACTS). Nearly all participants were subsequently genotyped on two polymorphic SNPs in the ADH1B and ADH1C loci known to affect in vitro ADH activity. In the DZ pairs, 14 microsatellite markers covering a 20.5 cM region on chromosome 4 that includes the ADH gene family were assessed, Variation in the timed series of autocorrelated blood and breath alcohol readings was studied using a bivariate simplex design. The contribution of a quantitative trait locus (QTL) or QTL's linked to the ADH region was estimated via a mixture of likelihoods weighted by identity-by-descent probabilities. The effects of allelic substitution at the ADH1B and ADH1C loci were estimated in the means part of the model simultaneously with the effects sex and age. There was a major contribution to variance in alcohol metabolism due to a QTL which accounted for about 64% of the additive genetic covariation common to both blood and breath alcohol readings at the first time point. No effects of the ADH1B*47His or ADH1C*349Ile alleles on in vivo metabolism were observed, although these have been shown to have major effects in vitro. This implies that there is a major determinant of variation for in vivo alcohol metabolism in the ADH region that is not accounted for by these polymorphisms. Earlier analyses of these data suggested that alcohol metabolism is related to drinking behavior and imply that this QTL may be protective against alcohol dependence.

Genome-wide scan of IQ finds significant linkage to a quantitative trait locus on 2q

A genome-wide linkage scan of 795 microsatellite markers (761 autosomal, 34 X chromosome) was performed on Multidimensional Aptitude Battery subtests and verbal, performance and full scale scores, the WAIS-R Digit Symbol subtest, and two word-recognition tests (Schonell Graded Word Reading Test, Cambridge Contextual Reading Test) highly predictive of IQ. The sample included 361 families comprising 2-5 siblings who ranged in age from 15.7 to 22.2 years; genotype, but not phenotype, data were available for 81% of parents. A variance components analysis which controlled for age and sex effects showed significant linkage for the Cambridge reading test and performance IQ to the same region on chromosome 2, with respective LOD scores of 4.15 and 3.68. Suggestive linkage (LOD score>2.2) for various measures was further supported on chromosomes 6, 7, 11, 14, 21 and 22. Where location of linkage peaks converged for IQ subtests within the same scale, the overall scale score provided increased evidence for linkage to that region over any individual subtest. Association studies of candidate genes, particularly those involved in neural transmission and development, will be directed to genes located under the linkage peaks identified in this study.

Linkage Analyses of Event-Related Potential Slow Wave Phenotypes Recorded in a Working Memory Task

Working memory is an essential component of wide-ranging cognitive functions. It is a complex genetic trait probably influenced by numerous genes that individually have only a small influence. These genes may have an amplified influence on phenotypes closer to the gene action. In this study, event-related potential (ERP) phenotypes recorded during a working-memory task were collected from 656 adolescents from 299 families for whom genotypes were available. Univariate linkage analyses using the MERLIN variance-components method were conducted on slow wave phenotypes recorded at multiple sites while participants were required to remember the location of a target. Suggestive linkage (LOD > 2.2) was found on chromosomes 4, 5, 6, 10, 17, and 20. After correcting for multiple testing, suggestive linkage remained on chromosome 10. Empirical thresholds were computed for the most promising phenotypes. Those on chromosome 10 remained suggestive. A number of genes reported to regulate neural differentiation and function (i.e. NRP1, ANK3, and CHAT) were found under these linkage peaks and may influence the levels of neural activity occurring in individuals participating in a spatial working-memory task.

A polymorphism in the promoter region of the human interleukin-16 gene is not associated with asthma or atopy in an Australian population

BACKGROUND

IL-16 is an immunomodulatory cytokine whose expression is increased in the bronchial mucosa, bronchoalveolar lavage fluid and induced sputum of asthmatic patients. It has been suggested that IL-16 has a regulatory role in the pathophysiology of asthma. A single-nucleotide polymorphism (T(-295)C) has been described in the promoter region of the gene and it has been hypothesized that this polymorphism may be associated with altered levels of IL-16 expression, and account for the increased levels of IL-16 seen in the asthmatic airway.

OBJECTIVE

To determine the association between the T(-295)C promoter polymorphism and asthma, disease severity and atopy in a large Australian Caucasian population.

METHODS

We used PCR and restriction fragment length polymorphism analysis to establish the allele frequency of the T(-295)C promoter polymorphism in a random Australian Caucasian population (n=176) and to characterize the polymorphism in a large Australian Caucasian population of mild (n=273), moderate (n=230) and severe (n=77) asthmatic patients, and non-asthmatic controls (n=455). Genotype association analyses were performed using chi(2) tests.

RESULTS

The polymorphic C allele was present in 19% of the asthmatic population and 21% of the non-asthmatic population. There was no association between the polymorphism and asthma (P=0.153) nor with asthma severity (P=0.417) or atopy (P=0.157) in this population.

CONCLUSION

Although it has been hypothesized that the T(-295)C promoter polymorphism may be associated with increased IL-16 gene expression, it is not associated with asthma, disease severity or atopy in this Australian population.

A functional polymorphism in the promoter region of the cyclooxygenase-2 gene is not associated with asthma and atopy in an Australian population

BACKGROUND

Cyclooxygenase (COX)-2 is a key inducible enzyme that regulates the production of anti-inflammatory prostaglandin E(2). A single-nucleotide polymorphism, -765G>C, located within a stimulatory protein-1 binding site in the COX-2 promoter region, has been shown to have significantly lower promoter activity in vitro compared with the wild-type and was associated with decreased plasma levels of C-reactive protein after coronary artery bypass surgery. We hypothesized that this polymorphism, which may result in decreased COX-2 transcription, could be associated with more severe asthma, and/or aspirin-intolerant asthma (AIA).

OBJECTIVE

To determine the association between the -765G>C COX-2 polymorphism and asthma, disease severity and AIA in a large, well-phenotyped Australian population.

METHODS

PCR and restriction fragment length polymorphism analysis was used to characterize the polymorphism in an Australian Caucasian population of patients with mild (n=322), moderate (n=254) or severe (n=88) asthma and in non-asthmatic control subjects (n=512), as well as in patients with AIA (n=58). Genotype and allele association analyses were performed using chi(2) tests.

RESULTS

The polymorphic -765C allele was present in approximately 30% of asthmatic patients and non-asthmatic controls. There was no association between the -765G>C polymorphism and asthma (P=0.920), disease severity (P=0.840), atopy (P=0.655) or AIA (P=0.841) in this population.

CONCLUSION

Although the -765G>C polymorphism may have lower promoter activity and result in decreased COX-2 expression, it is not associated with asthma, disease severity, AIA or atopy in this Australian population.

A major quantitative trait locus for CD4-CD8 ratio is located on chromosome 11

CD4-CD8 ratio is an important diagnostic measure of immune system functioning. In particular, CD4-CD8 ratio predicts the time taken for progression of HIV infection to acquired immune deficiency syndrome (AIDS) and the long-term survival of AIDS patients. To map genes that regulate differences between healthy individuals in CD4-CD8 ratio, we typed 757 highly polymorphic microsatellite markers at an average spacing of approximately 5 cM across the genome in 405 pairs of dizygotic twins at ages 12, 14 and 16. We used multipoint variance components linkage analysis to test for linkage between marker loci and CD4-CD8 ratio at each age. We found suggestive evidence of linkage on chromosome 11p in 12-year-old twins (LOD=2.55, P=0.00031) and even stronger evidence of linkage in the same region at age 14 (LOD=3.51, P=0.00003). Possible candidate genes include CD5 and CD6, which encode cell membrane proteins involved in the positive selection of thymocytes. We also found suggestive evidence of linkage at other areas of the genome including regions on chromosomes 1, 3, 4, 5, 6, 12, 13, 15, 17 and 22.

Ocular melanoma is not associated with CDKN2A or MC1R variants--a population-based study

Germline variants in the melanocortin 1 receptor gene (MC1R) and the p16 gene (CDKN2A) are associated with an increased risk of cutaneous melanoma. The frequency of these germline variants was examined in a population-based, incident series of 62 ocular melanoma cases and ethnicity-matched population controls. In both cases and controls, 59% of individuals carried at least one MC1R variant and there were no significant differences in the frequency of any of the five most common variants of MC1R. We also found no significant differences between cases and controls in the frequency of any of the four most common variants of CDKN2A, and no melanoma case carried a deleterious germline CDKN2A mutation. Our findings argue against an important predisposing effect of the MC1R and CDKN2A genes for ocular melanoma.

Genetic association and cellular function of MC1R variant alleles in human pigmentation

We have examined MC1R variant allele frequencies in the general population of South East Queensland and in a collection of adolescent dizygotic and monozygotic twins and family members to define statistical associations with hair and skin color, freckling, and mole count. Results of these studies are consistent with a linear recessive allelic model with multiplicative penetrance in the inheritance of red hair. Four alleles, D84E, R151C, R160W, and D294H, are strongly associated with red hair and fair skin with multinomial regression analysis showing odds ratios of 63, 118, 50, and 94, respectively. An additional three low-penetrance alleles V60L, V92M, and R163Q have odds ratios 6, 5, and 2 relative to the wild-type allele. To address the cellular effects of MC1R variant alleles in signal transduction, we expressed these receptors in permanently transfected HEK293 cells. Measurement of receptor activity via induction of a cAMP-responsive luciferase reporter gene found that the R151C and R160W receptors were active in the presence of NDP-MSH ligand, but at much reduced levels compared with that seen with the wild-type receptor. The ability to stimulate phosphorylation of the cAMP response element binding protein (CREB) transcription factor was also apparent in all stimulated MC1R variant allele-expressing HEK293 cell extracts as assessed by immunoblotting. In contrast, human melanoma cell lines showed wide variation in the their ability to undergo cAMP-mediated CREB phosphorylation. Culture of human melanocytes of known MC1R genotype may provide the best experimental approach to examine the functional consequences for each MC1R variant allele. With this objective, we have established more than 300 melanocyte cell strains of defined MC1R genotype.

Evidence for the genetic control of immunoglobulin E reactivity to the allergens of Alternaria alternata

BACKGROUND

The fungus Alternaria alternata contains potent allergens, and sensitization to these allergens is associated with a high risk of respiratory disease. The influence of genetic regulation on sensitization to Alternaria is unknown.

OBJECTIVE

To determine the influence of genetic factors on IgE responses to specific allergens of Alternaria.

METHODS

The concordance of skin prick test (SPT), radioallergosorbent test (RAST) and IgE-binding profiles of sera were examined from a large cohort of monozygotic and dizygotic twins.

RESULTS

Casewise concordance for a positive SPT response was monozygous (MZ) 66%: dizygous (DZ) 40% (P = 0.002). Logistic regression confirmed that casewise concordance was significantly stronger between MZ than DZ pairs. Immunoblotting against an Alternaria extract revealed 19 allergenic bands. The differences in concordance between the different bands were not significant for either the MZ (P = 0.97) or DZ (P = 0.84) groups. The pooled MZ : DZ difference in concordance was just significant (P = 0.049), suggesting an overall genetic effect on the response to Alternaria. This was reinforced by the comparison of the MZ and DZ correlations for total number of bands recognized (MZ r = 0.65; DZ r = 0.37, P = 0.015). Overall, there was a moderate correlation between the individual SPT weal size and RAST score (r(2) = 0.41) and a substantial correlation between the number of immunoblotted bands and RAST scores (r(2) = 0.79).

CONCLUSION

There is a strong genetic influence on IgE response to the mixture of Alternaria allergens and a lesser effect on IgE response to individual allergens.

Applying statistical approaches in the dissection of genes versus environment for asthma and allergic disease

Now that some of the genes involved in asthma and allergy have been identified, interest is turning to how genetic predisposition interacts with exposure to environmental risk factors. These questions are best answered by studies in which both genotypes and other risk factors are measured, but even simpler studies, in which family history is used as a proxy for genotype, have made suggestive findings. For example, early breast feeding may increase the risk of allergic disease in genetically susceptible children, and decrease the risk of 'sporadic' allergy. This review also addresses the overall importance of genetic causes of allergic disease in the general population.

Variation in alcohol pharmacokinetics as a risk factor for alcohol dependence

BACKGROUND

The significant association between alcohol dehydrogenase (ADH)-2 genotype and alcohol-dependence risk, demonstrated in both Asian and non-Asian populations, suggests a link between the metabolism of alcohol (ethanol) and individual differences in susceptibility to dependence.

METHODS

We tested this hypothesis by following up on subjects who took part in the Alcohol Challenge Twin Study conducted in 1979-1981 and comparing the blood and breath alcohol results in that study between subjects who subsequently did or did not meet diagnostic criteria for lifetime alcohol dependence in 1992-1993.

RESULTS

Subjects who met DSM-III-R criteria for lifetime alcohol dependence at follow-up had higher blood and breath alcohol values after alcohol challenge than never-dependent subjects. Multivariate analysis showed independent effects of susceptibility to alcohol dependence and smoking status on blood alcohol concentrations, whereas habitual alcohol intake at the time of the initial study had marginally significant effects. The risk of alcohol dependence was 2-fold higher in men and 3-fold higher in women with blood or breath alcohol concentrations in the highest quartile than in the lowest quartile.

CONCLUSIONS

In view of this association and the known genetic influences on both alcohol pharmacokinetics and alcohol dependence, it is probable that part of the heritability of dependence is mediated by genes (other than the known ADH2 and ADH3 polymorphisms) affecting alcohol metabolism.

Human twinning is not linked to the region of chromosome 4 syntenic with the sheep twinning gene FecB

The tendency to dizygotic (DZ) twinning is inherited in both humans and sheep, and a fecundity gene in sheep (FecB) maps to sheep chromosome 6, syntenic with human 4q21-25. Our aim was to see whether a gene predisposing to human DZ twinning mapped to this region. DNA was collected from 169 pairs and 17 sets of 3 sisters (trios) from Australia and New Zealand who had each had spontaneous DZ twins, mostly before the age of 35, and from a replication sample of 111 families (92 affected sister pairs) from The Netherlands. Exclusion mapping was carried out after typing 26 markers on chromosome 4, of which 8 spanned the region likely to contain the human homologue of the sheep FecB gene. We used nonparametric affected sib pair methods for linkage analysis [ASPEX 2.2, Hinds and Risch, 1999]. Complete exclusion of linkage (lod < -2) of a gene conferring a relative risk for sibs as low as 1.5 (lambda(s) > 1.5) was obtained for all but the p terminus region on chromosome 4. Exclusion in the syntenic region was stronger, down to lambda(s) = 1.3. We concluded that if there is a gene influencing DZ twinning on chromosome 4, its effect must be minor.

Increasing the response rate to a mailed questionnaire by including more stamps on the return envelope: a cotwin control study

Twins taking part in two unrelated studies were sent a questionnaire together with a self-addressed envelope that either carried one or multiple (up to 5) stamps to the same value. The unprompted proportion of questionnaires returned (before commencement of telephone reminder calls) was increased from 62% to 71% in one study, and from 43% to 52% in the other study (test for common odds ratio in studies, p = 0.04).

Mutations in the follicle-stimulating hormone receptor and familial dizygotic twinning

Concentrations of follicle-stimulating hormone (FSH) have an important role in multiple ovulation. An association has been reported between mutations in the FSH receptor (FSHR) in a family with increased twinning frequency. We sequenced the transmembrane region of FSHR (located on chromosome 2) in 21 unrelated mothers of dizygotic twins and found no differences to the published sequence. A linkage study of 183 sister pairs and trios, in which all sisters had given birth to spontaneous dizygotic twins, excluded linkage to this region of chromosome 2. We conclude that mutations in FSHR are not a common cause of familial dizygotic twinning.

Melanocortin-1 receptor genotype is a risk factor for basal and squamous cell carcinoma

MC1R gene variants have previously been associated with red hair and fair skin color, moreover skin ultraviolet sensitivity and a strong association with melanoma has been demonstrated for three variant alleles that are active in influencing pigmentation: Arg151Cys, Arg160Trp, and Asp294His. This study has confirmed these pigmentary associations with MC1R genotype in a collection of 220 individuals drawn from the Nambour community in Queensland, Australia, 111 of whom were at high risk and 109 at low risk of basal cell carcinoma and squamous cell carcinoma. Comparative allele frequencies for nine MC1R variants that have been reported in the Caucasian population were determined for these two groups, and an association between prevalence of basal cell carcinoma, squamous cell carcinoma, solar keratosis and the same three active MC1R variant alleles was demonstrated [odds ratio = 3.15 95% CI (1.7, 5.82)]. Three other commonly occurring variant alleles: Val60Leu, Val92Met, and Arg163Gln were identified as having a minimal impact on pigmentation phenotype as well as basal cell carcinoma and squamous cell carcinoma risk. A significant heterozygote effect was demonstrated where individuals carrying a single MC1R variant allele were more likely to have fair and sun sensitive skin as well as carriage of a solar lesion when compared with those individuals with a consensus MC1R genotype. After adjusting for the effects of pigmentation on the association between MC1R variant alleles and basal cell carcinoma and squamous cell carcinoma risk, the association persisted, confirming that presence of at least one variant allele remains informative in terms of predicting risk for developing a solar-induced skin lesion beyond that information wained through observation of pigmentation phenotype.

Natural selection and quantitative genetics of life-history traits in Western women: a twin study

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection will cause a change among women in a contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the "baby boom" phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.

Dizygotic twinning is not linked to variation at the alpha-inhibin locus on human chromosome 2

Natural multiple pregnancy in women leading to dizygotic (DZ) twins is familial and varies across racial groups, suggesting a genetic predisposition. Mothers of DZ twins have a higher incidence of spontaneous multiple ovulation and elevated FSH concentrations. FSH release is controlled by feedback of inhibin peptides from the ovary, and immunization against inhibin alpha-subunit results in an increased ovulation rate in animals. The inhibin alpha-subunit is therefore a candidate gene for mutations that may increase the frequency of DZ twinning. Restriction digests of a PCR product from exon 1 with the enzyme SpeI detects a C/T polymorphism at bp 128 with two alleles of 447 and 323/124 bp. The polymorphism was typed in 1,125 individuals from 326 pedigrees with 717 mothers of spontaneous DZ twins. The alpha-inhibin locus mapped within 3 centimorgans of D2S164, and linkage with DZ twinning was excluded [decimal log odds ratio (LOD) score, -2.81 at theta = 0]. There was complete exclusion of linkage (LOD, less than -2) of a gene conferring relative risk 1.8 (lambdas, >1.8) across the chromosome, except at the p-terminus region and a small peak (maximum LOD score, 0.6) in the region of D2S151-D2S326. Analysis using either recessive or dominant models excluded linkage with DZ twinning in this population (LOD score, less than -2.5) across chromosome 2. We conclude that dizygotic twinning is not linked to variation in the alpha-inhibin locus. The results also suggest that mutations in other candidates on chromosome 2, including the receptor for FSH and the betaB-inhibin subunit (INHBB) cannot be major contributors to risk for DZ twinning.

A comprehensive analysis of complex traits in problem 2A

We used descriptive analysis to investigate the relationship between affection status and five quantitative traits (Q1-Q5) in Problem 2A and results suggested the five quantitative traits fall into two groups. The first group comprised three strongly correlated traits, Q1-Q3, which underlie affection status, and the second group comprised Q4 and Q5, which are not directly related to affection status. Segregation and linkage analyses of traits Q1-Q3 and affection status from the first replicate detected one of the major loci for Q1 (MG1) linked to marker 14 on chromosome 5 (D5G14). Because our segregation analysis failed to show evidence of a major locus effect on Q2, and we overlooked the interaction between MG3 and sex, we did not detect either MG2 or MG3. Using Haseman-Elston sib-pair analysis [Haseman and Elston, 1972], we also examined the statistical power of Q1 and type I error rate (using the environmental factor as an index), for the remaining 199 replicates in the context of a genome screen.

No common major gene for apolipoprotein A-I and HDL3-C levels: evidence from bivariate segregation analysis

Apolipoprotein A-I (apo A-I) is the most abundant protein in high-density lipoprotein (HDL) particles, and it plays an important role in HDL metabolism. Both apo A-I and HDL cholesterol (HDL-C) levels are inversely associated with risk of cardiovascular disease. Segregation analyses suggest apo A-I levels are under the control of one or more major loci. Since HDL particles are heterogeneous in their composition and size, genetic influence on its subfractions (i.e., HDL2 and HDL3) could vary. A previous report showed evidence of a major locus controlling HDL3-C levels in a subset of the current study population. Because quantitative trait loci involved in complex diseases are likely to have pleiotropic effects on several related traits, it is possible to have a common major gene involved in regulating apo A-I and HDL3-C levels. We performed a bivariate segregation analysis of apo A-I and HDL3-C levels in 1,006 individuals from 137 families ascertained through probands undergoing elective, diagnostic coronary angiography at the Johns Hopkins Hospital. The results showed significant genetic correlation between these two traits, but the hypothesis of a common major gene was rejected. Bivariate segregation analysis favored a model with two genes controlling apo A-I and a third gene independently controlling HDL3-C, and the genetic correlation between these two traits is due to residual additive polygenes. Overall, results from this study suggest that there are distinct genetic mechanisms for apo A-I and HDL3-C levels. Future studies, especially linkage analysis, should consider distinct genetic mechanisms and multiple major gene loci.

Genetic analysis of the age at menopause by using estimating equations and Bayesian random effects models

Multi-wave self-report data on age at menopause in 2182 female twin pairs (1355 monozygotic and 827 dizygotic pairs), were analysed to estimate the genetic, common and unique environmental contribution to variation in age at menopause. Two complementary approaches for analysing correlated time-to-onset twin data are considered: the generalized estimating equations (GEE) method in which one can estimate zygosity-specific dependence simultaneously with regression coefficients that describe the average population response to changing covariates; and a subject-specific Bayesian mixed model in which heterogeneity in regression parameters is explicitly modelled and the different components of variation may be estimated directly. The proportional hazards and Weibull models were utilized, as both produce natural frameworks for estimating relative risks while adjusting for simultaneous effects of other covariates. A simple Markov chain Monte Carlo method for covariate imputation of missing data was used and the actual implementation of the Bayesian model was based on Gibbs sampling using the freeware package BUGS.

Effects of HFE C282Y and H63D polymorphisms and polygenic background on iron stores in a large community sample of twins

The aim of this study was to assess and to compare the role of HFE polymorphisms and other genetic factors in variation in iron stores. Blood samples were obtained from 3,375 adult male and female twins (age range 29-82 years) recruited from the Australian Twin Registry. There were 1,233 complete pairs (562 monozygotic and 571 dizygotic twins). Serum iron, transferrin, transferrin saturation with iron, and ferritin were measured, and the HFE C282Y and H63D genotypes were determined. The frequency of the C282Y allele was.072, and that of the H63D allele was.141. Significant sources of variation in the indices of iron status included age, sex, age-sex interaction, body-mass index, and both the C282Y and H63D genotypes. The iron, transferrin, and saturation values of CC and CY subjects differed significantly, but the ferritin values did not. After correction for age and body-mass index, 23% and 31% of the variance in iron, 66% and 49% of the variance in transferrin, 33% and 47% of the variance in transferrin saturation, and 47% and 47% of the variance in ferritin could be explained by additive genetic factors, for men and women, respectively. HFE C282Y and H63D variation accounted for <5% of the corrected phenotypic variance, except for saturation (12% in women and 5% in men). We conclude that HFE CY and HD heterozygotes differ in iron status from the CC and HH homozygotes and that serum transferrin saturation is more affected than is serum ferritin. There are highly significant effects of other as-yet-unidentified genes on iron stores, in addition to HFE genotype.

Does sex or photoperiodic condition influence ZENK induction in response to song in European starlings?

Variables such as the photoperiod a bird experiences, or its sex, affect behavioral responses to song. The present experiment investigated whether song-induced expression of the immediate-early gene ZENK is also influenced by sex or photoperiod. We examined the expression of the protein product of ZENK in wild-caught male and female European starlings (Sturnus vulgaris) in different photoperiodic conditions. In the first experiment, adult reproductively active male and female starlings were presented with either conspecific male song or no song in experimental chambers. In the second experiment, conspecific male song was presented to reproductively active and reproductively inactive adult female starlings. Localization of the ZENK protein product revealed that song stimulation resulted in a significant increase in the number of ZENK immunoreactive (-ir) cells in the caudomedial neostriatum (NCM) and the caudomedial hyperstriatum ventrale (cmHV) compared with unstimulated birds. No differences in the number of ZENK-ir neurons were observed between males and females or between reproductively active and inactive females. Thus, the present data indicate that the number of cells expressing ZENK in NCM and cmHV following song playback does not vary with sex or photoperiod in starlings.

Validation of a new antiserum directed towards the synthetic c-terminus of the FOS protein in avian species: immunological, physiological and behavioral evidence

In the past 10 years, the study of the expression of immediate early genes, such as c-fos, in the brain has become a common method for the identification of brain areas involved in the regulation of specific physiological and behavioral functions. The use of this method in avian species has been limited by the paucity of suitable antibodies that cross-react with the FOS protein in birds. We describe in this paper the preparation of an antibody directed against a synthetic fragment of the protein product of the c-fos gene in chickens (Gallus domesticus). We demonstrate that this new antibody can be used in several avian species to study FOS expression induced by a variety of pharmacological, physiological and behavioral stimuli. Western blot studies indicated that this antibody recognizes a protein of the expected size (47 kDa) but also cross reacts to some extent with proteins of lower molecular weight that share sequence homology with FOS (Fos-related antigens). FOS immunocytochemistry was performed with this antibody in four species of birds in three different laboratories utilizing diverse variants of the immunocytochemical procedure. In all cases the antibody provided a reliable identification of the FOS antigen. The new antibody described here appears to be suitable for the study of FOS expression in several different avian species and situations. It is available in substantial amounts and will therefore make it possible to use FOS expression as a tool to map brain activity in birds as has now been done for several years in mammalian species.

A major quantitative-trait locus for mole density is linked to the familial melanoma gene CDKN2A: a maximum-likelihood combined linkage and association analysis in twins and their sibs

Important risk factors for melanoma are densely clustered melanocytic nevi (common moles) and mutations in the p16 (CDKN2A) gene. Nevi may be subclassified as raised or flat. In our sample, raised nevi were 27% of the total, and the two kinds had a correlation of.33. Correlations for total-nevus count (TNC) in 153 MZ and 199 DZ twin pairs were.94 and.60, respectively, which are compatible with a very-high degree of genetic determination. We hypothesized that some of the genetic variance might be due to variation in the p16 gene. Analysis of linkage to a highly polymorphic marker (D9S942), located close to p16, detected quantitative-trait-loci (QTL) effects accounting for 27% of variance in TNC, rising to 33% if flat but not raised moles were considered. Total heritability was higher for raised (.69) than for flat (.42) moles, but QTL linkage was 0 for raised moles, whereas it accounted for 80% of the heritability of flat moles; additionally, family environment accounted for only 15% of variance in raised versus 46% in flat moles. These findings suggest that raised and flat nevi have very different etiologies. Longer alleles at D9S942 were associated with higher flat-mole counts, and a novel modification to a within-sibship association test showed that this association is genuine and not due to population stratification, although it accounts for only 1% of total variance. Since germline mutations in the exons of CDKN2A are rare, it is likely that variants in the noncoding regions of this gene, or in another gene nearby, are responsible for this major determinant of moliness and, hence, of melanoma risk.