The urgent need for a harmonized severity scoring system for acute allergic reactions.

The accurate assessment and communication of the severity of acute allergic reactions are important to patients, clinicians, researchers, the food industry, and public health and regulatory authorities. Severity has different meanings to different stakeholders with patients and clinicians rating the significance of particular symptoms very differently. Many severity scoring systems have been generated, most focusing on the severity of reactions following exposure to a limited group of allergens. They are heterogeneous in format, none has used an accepted developmental approach, and none has been validated. Their wide range of outcome formats has led to difficulties with interpretation and application. Therefore, there is a persisting need for an appropriately developed and validated severity scoring system for allergic reactions that work across the range of allergenic triggers and address the needs of different stakeholder groups. We propose a novel approach to develop and then validate a harmonized scoring system for acute allergic reactions, based on a data-driven method that is informed by clinical and patient experience and other stakeholders' perspectives. We envisage two formats: (i) a numerical score giving a continuum from mild to severe reactions that are clinically meaningful and are useful for allergy healthcare professionals and researchers, and (ii) a three-grade-based ordinal format that is simple enough to be used and understood by other professionals and patients. Testing of reliability and validity of the new approach in a range of settings and populations will allow eventual implementation of a standardized scoring system in clinical studies and routine practice.

The Allergic Rhinitis and its Impact on Asthma (ARIA) score of allergic rhinitis using mobile technology correlates with quality of life: The MASK study.

Mobile technology has been used to appraise allergic rhinitis control, but more data are needed. To better assess the importance of mobile technologies in rhinitis control, the ARIA (Allergic Rhinitis and its Impact on Asthma) score ranging from 0 to 4 of the Allergy Diary was compared with EQ-5D (EuroQuol) and WPAI-AS (Work Productivity and Activity Impairment in allergy) in 1288 users in 18 countries. This study showed that quality-of-life data (EQ-5D visual analogue scale and WPA-IS Question 9) are similar in users without rhinitis and in those with mild rhinitis (scores 0-2). Users with a score of 3 or 4 had a significant impairment in quality-of-life questionnaires.

The sex-shift in single disease and multimorbid asthma and rhinitis during puberty - a study by MeDALL.

BACKGROUND: Cross-sectional studies suggested that allergy prevalence in childhood is higher in boys compared to girls, but it remains unclear whether this inequality changes after puberty. We examined the sex-specific prevalence of asthma and rhinitis as single and as multimorbid diseases before and after puberty onset in longitudinal cohort data. METHODS: In six European population-based birth cohorts of MeDALL, we assessed the outcomes: current rhinitis, current asthma, current allergic multimorbidity (ie, concurrent asthma and rhinitis), puberty status and allergic sensitization by specific serum antibodies (immunoglobulin E) against aero-allergens. With generalized estimating equations, we analysed the effects of sex, age, puberty (yes/no) and possible confounders on the prevalence of asthma and rhinitis, and allergic multimorbidity in each cohort separately and performed individual participant data meta-analysis. FINDINGS: We included data from 19 013 participants from birth to age 14-20 years. Current rhinitis only affected girls less often than boys before and after puberty onset: adjusted odds ratio for females vs males 0.79 (95%-confidence interval 0.73-0.86) and 0.86 (0.79-0.94), respectively (sex-puberty interaction P = .089). Similarly, for current asthma only, females were less often affected than boys both before and after puberty onset: 0.71, 0.63-0.81 and 0.81, 0.64-1.02, respectively (sex-puberty interaction P = .327). The prevalence of allergic multimorbidity showed the strongest sex effect before puberty onset (female-male-OR 0.55, 0.46-0.64) and a considerable shift towards a sex-balanced prevalence after puberty onset (0.89, 0.74-1.04); sex-puberty interaction: P < .001. INTERPRETATION: The male predominance in prevalence before puberty and the "sex-shift" towards females after puberty onset were strongest in multimorbid patients who had asthma and rhinitis concurrently.

Google Trends terms reporting rhinitis and related topics differ in European countries.

Google Trends (GT) searches trends of specific queries in Google and reflects the real-life epidemiology of allergic rhinitis. We compared Google Trends terms related to allergy and rhinitis in all European Union countries, Norway and Switzerland from 1 January 2011 to 20 December 2016. The aim was to assess whether the same terms could be used to report the seasonal variations of allergic diseases. Using the Google Trend 5-year graph, an annual and clear seasonality of queries was found in all countries apart from Cyprus, Estonia, Latvia, Lithuania and Malta. Different terms were found to demonstrate seasonality depending on the country - namely 'hay fever', 'allergy' and 'pollen' - showing cultural differences. A single set of terms cannot be used across all European countries, but allergy seasonality can be compared across Europe providing the above three terms are used. Using longitudinal data in different countries and multiple terms, we identified an awareness-related spike of searches (December 2016).

The independent role of prenatal and postnatal exposure to active and passive smoking on the development of early wheeze in children.

Maternal smoking during pregnancy increases childhood asthma risk, but health effects in children of nonsmoking mothers passively exposed to tobacco smoke during pregnancy are unclear. We examined the association of maternal passive smoking during pregnancy and wheeze in children aged ≤2 years.Individual data of 27 993 mother-child pairs from 15 European birth cohorts were combined in pooled analyses taking into consideration potential confounders.Children with maternal exposure to passive smoking during pregnancy and no other smoking exposure were more likely to develop wheeze up to the age of 2 years (OR 1.11, 95% CI 1.03-1.20) compared with unexposed children. Risk of wheeze was further increased by children's postnatal passive smoke exposure in addition to their mothers' passive exposure during pregnancy (OR 1.29, 95% CI 1.19-1.40) and highest in children with both sources of passive exposure and mothers who smoked actively during pregnancy (OR 1.73, 95% CI 1.59-1.88). Risk of wheeze associated with tobacco smoke exposure was higher in children with an allergic versus nonallergic family history.Maternal passive smoking exposure during pregnancy is an independent risk factor for wheeze in children up to the age of 2 years. Pregnant females should avoid active and passive exposure to tobacco smoke for the benefit of their children's health.

Cor a 14 is the superior serological marker for hazelnut allergy in children, independent of concomitant peanut allergy.

BACKGROUND: Hazelnut is the most frequent cause of tree nut allergy, but up to half of all children with hazelnut allergy additionally suffer from peanut allergy. Our aim was to identify diagnostic values of the most promising serological markers (Cor a 9 and Cor a 14) and to address the influence of concomitant peanut allergy and PR10 sensitization. METHOD: We included 155 children suspected of hazelnut allergy and challenged according to the guidelines. Concomitant allergy to peanuts was verified or ruled out by challenge. Skin prick test, s-IgE and CRD to hazelnut, peanut, PR10 and LPT protein families were measured using ImmunoCAP. RESULTS: Sixty-five children had a positive hazelnut challenge, and 60% of these also had a concomitant peanut allergy. Children allergic to hazelnut were sensitized to Cor a 9 and Cor a 14; peanut-allergic children were sensitized to Ara h 2. Sensitization to PR10 protein components was seen in 45% of all included children, irrelevant to allergy to peanut or hazelnut. A cut-off >0.72 kU/L of IgE towards Cor a 14 diagnosed 87% correctly, making Cor a 14 the superior serology marker. However, nine hazelnut-allergic children were primarily sensitized to Cor a 9. CONCLUSION: Concomitant peanut allergy is common in hazelnut-allergic children, but decision points as well as diagnostic values for Cor a 14 are not affected. We found three independent and well-characterized serotypes; hazelnut-allergic children were sensitized to Cor a 14, peanut-allergic children were sensitized to Ara h 2, and independently of this were children sensitized to birch pollen (Bet v 1).

Phenotyping asthma, rhinitis and eczema in MeDALL population-based birth cohorts: an allergic comorbidity cluster.

BACKGROUND: Asthma, rhinitis and eczema often co-occur in children, but their interrelationships at the population level have been poorly addressed. We assessed co-occurrence of childhood asthma, rhinitis and eczema using unsupervised statistical techniques. METHODS: We included 17 209 children at 4 years and 14 585 at 8 years from seven European population-based birth cohorts (MeDALL project). At each age period, children were grouped, using partitioning cluster analysis, according to the distribution of 23 variables covering symptoms 'ever' and 'in the last 12 months', doctor diagnosis, age of onset and treatments of asthma, rhinitis and eczema; immunoglobulin E sensitization; weight; and height. We tested the sensitivity of our estimates to subject and variable selections, and to different statistical approaches, including latent class analysis and self-organizing maps. RESULTS: Two groups were identified as the optimal way to cluster the data at both age periods and in all sensitivity analyses. The first (reference) group at 4 and 8 years (including 70% and 79% of children, respectively) was characterized by a low prevalence of symptoms and sensitization, whereas the second (symptomatic) group exhibited more frequent symptoms and sensitization. Ninety-nine percentage of children with comorbidities (co-occurrence of asthma, rhinitis and/or eczema) were included in the symptomatic group at both ages. The children's characteristics in both groups were consistent in all sensitivity analyses. CONCLUSION: At 4 and 8 years, at the population level, asthma, rhinitis and eczema can be classified together as an allergic comorbidity cluster. Future research including time-repeated assessments and biological data will help understanding the interrelationships between these diseases.

Clinical value of component-resolved diagnostics in peanut-allergic patients.

INTRODUCTION: As replacement for the oral food challenge, decision-points for sensitization test have been established, but suboptimal sensitivity and/or specificity, as well as regional differences, have reduced the clinical usability. IgE toward specific peanut protein components has been reported to be of value, but data on correlation with clinical data are sparse. Our aim was to correlate IgE values with the outcome of peanut challenges. METHOD: Data from 175 positive and 30 negative peanut challenges in patients aged 1-26 years were retrospectively correlated with the levels of specific IgE to peanut and peanut components (Ara h 1-3, h 8, and h 9). RESULT: The best correlation between IgE and clinical thresholds was found for Ara h 2 (ρ(s) = -0.30, P < 0.01). A cutoff of Ara h 2 > 1.63 kU/l yielded a specificity = 1.00, with a corresponding sensitivity of 0.70. Symptom severity elicited during challenge correlated significantly with the levels of Ara h 2 (ρ(s) = 0.60, P < 0.0001), but large individual variation was found. CONCLUSION: The level of IgE toward Ara h 2 can improve diagnostic accuracy by introducing a more clear-cut decision-point with an optimal specificity maintaining a high sensitivity. In our study, this would have reduced the necessary number of challenges to be performed from 205 to 92. Extrapolation between centers is difficult and decision-points need to be addressed in relation to settings and population. Further component-resolved diagnostic cannot replace oral challenge neither in determining thresholds nor in the assessment of severity of symptoms elicited during challenge.

Meta-analysis of mould and dampness exposure on asthma and allergy in eight European birth cohorts: an ENRIECO initiative.

BACKGROUND: Several cross-sectional studies during the past 10 years have observed an increased risk of allergic outcomes for children living in damp or mouldy environments. OBJECTIVE: The objective of this study was to investigate whether reported mould or dampness exposure in early life is associated with the development of allergic disorders in children from eight European birth cohorts. METHODS: We analysed data from 31 742 children from eight ongoing European birth cohorts. Exposure to mould and allergic health outcomes were assessed by parental questionnaires at different time points. Meta-analyses with fixed- and random-effect models were applied. The number of the studies included in each analysis varied based on the outcome data available for each cohort. RESULTS: Exposure to visible mould and/or dampness during first 2 years of life was associated with an increased risk of developing asthma: there was a significant association with early asthma symptoms in meta-analyses of four cohorts [0-2 years: adjusted odds ratios (aOR), 1.39 (95% CI, 1.05-1.84)] and with asthma later in childhood in six cohorts [6-8 years: aOR, 1.09 (95% CI, 0.90-1.32) and 3-10 years: aOR, 1.10 (95% CI, 0.90-1.34)]. A statistically significant association was observed in six cohorts with symptoms of allergic rhinitis at school age [6-8 years: aOR, 1.12 (1.02-1.23)] and at any time point between 3 and 10 years [aOR, 1.18 (1.09-1.28)]. CONCLUSION: These findings suggest that a mouldy home environment in early life is associated with an increased risk of asthma particularly in young children and allergic rhinitis symptoms in school-age children.

Viruses and bacteria in acute asthma exacerbations--a GA² LEN-DARE systematic review.

A major part of the burden of asthma is caused by acute exacerbations. Exacerbations have been strongly and consistently associated with respiratory infections. Respiratory viruses and bacteria are therefore possible treatment targets. To have a reasonable estimate of the burden of disease induced by such infectious agents on asthmatic patients, it is necessary to understand their nature and be able to identify them in clinical samples by employing accurate and sensitive methodologies. This systematic review summarizes current knowledge and developments in infection epidemiology of acute asthma in children and adults, describing the known impact for each individual agent and highlighting knowledge gaps. Among infectious agents, human rhinoviruses are the most prevalent in regard to asthma exacerbations. The newly identified type-C rhinoviruses may prove to be particularly relevant. Respiratory syncytial virus and metapneumovirus are important in infants, while influenza viruses seem to induce severe exacerbations mostly in adults. Other agents are relatively less or not clearly associated. Mycoplasma and Chlamydophila pneumoniae seem to be involved more with asthma persistence rather than with disease exacerbations. Recent data suggest that common bacteria may also be involved, but this should be confirmed. Although current information is considerable, improvements in detection methodologies, as well as the wide variation in respect to location, time and populations, underline the need for additional studies that should also take into account interacting factors.

Copper and zinc balance in exercising horses fed 2 forms of mineral supplements.

Studies comparing the absorption and retention of various forms of trace minerals in horses have yielded mixed results. The objective of this study was to compare Cu and Zn absorption and retention in exercising horses where the mineral was supplemented in the sulfate or organic chelate form. Nine mature horses were used in a modified switchback design experiment consisting of seven 28-d periods. Horses were fed a diet consisting of 50% concentrate and 50% hay that was balanced to meet the energy, protein, Ca, and P requirements for horses performing moderate-intensity exercise. Horses were subjected to a controlled mineral repletion-depletion diet sequence before feeding the experimental diet to standardize mineral status across horses. The experimental diet was designed to provide 90% of the 1989 NRC for Cu and Zn, with supplemental mineral provided in the inorganic sulfate form (CuSO(4) and ZnSO(4)) or the organic chelate form (Cu-Lys and Zn-Met). Feed, fecal, urine, and water samples collected during a total collection during the last 4 d of the experimental diet periods were analyzed to determine apparent absorption and retention of Cu and Zn from the 2 mineral forms. A formulation error caused horses receiving the organic chelate diet to consume about 3 times the amount of Cu and Zn compared with those fed the sulfate-supplemented diet. Copper and Zn intake and fecal excretion were greater (P < 0.05) for horses consuming the organic chelate-supplemented diet. Apparent absorption values for all horses were negative. Apparent Cu absorption and retention as a percentage of intake were greater for horses fed the organic chelate diet (P < 0.05). It is unknown why excretion of Cu and Zn by the horses during the total collection exceeded the mineral intake. Although Cu-Lys seemed to be better absorbed than CuSO(4) and absorption of Zn-Met and ZnSO(4) were not different, these results are tempered by the observation of abnormally high fecal and urinary excretion values for Cu and Zn in the present study.

Food allergy and food sensitization in early childhood: results from the DARC cohort.

BACKGROUND: The prevalence of food hypersensitivity (FHS) and the relationship with atopic dermatitis (AD) is controversial. The aim of this study was to determine the development of FHS and to correlate this with AD in relation to sensitization and symptoms. METHODS: This study combines new data from birth to 18 months of age with previous published results from 3 and 6 years. The Danish Allergy Research Centre cohort, including 562 children, is a unique, population-based, prospective birth cohort, with clinical examinations at all follow-ups. All children were examined for the development of AD using Hanifin-Rajka criteria and for FHS using interviews, skin prick test (SPT), specific immunoglobulin E (IgE), and food challenge according to EAACI guidelines. RESULTS: Twenty children were confirmed with FHS to milk, egg, and peanut. FHS peaked at 18 months (3.6%) and then decreased to 1.2% at 72 months of age. No new cases were found after 3 years. Self-reporting could only be confirmed in 31% of cases. Among the 122 children with AD, 18 had FHS (14.8%). FHS was IgE-mediated in 95% of the cases but 16 of 20 children were additionally sensitized to other foods which they tolerated. Children with AD were neither more IgE-sensitized nor had higher levels of IgE when compared with healthy children but they were more persistently sensitized. CONCLUSIONS: Sensitization to foods in young children without food allergy seems to be a normal phenomenon. The discrepancy between sensitization, self-reported food-related symptoms and confirmed FHS illustrates the need to perform standardized oral challenges in order to confirm the diagnosis of FHS.

Meta-analysis of determinants for pet ownership in 12 European birth cohorts on asthma and allergies: a GA2LEN initiative.

BACKGROUND: Studies on pet ownership as a risk or protective factor for asthma and allergy show inconsistent results. This may be on account of insufficient adjustment of confounding factors. AIM: The objective of this study was to describe determinants of cat and dog ownership in European families with and without allergies. METHODS: Within the EU-funded network of excellence GA(2)LEN, we performed meta-analyses with data from 12 ongoing European birth cohort studies on asthma and allergy. Each of the birth cohort studies enrolled between 485 and 4089 children. Pet ownership, allergic status (asthma, allergic rhinitis, eczema) of parents and siblings, parental education, access to ground floor, and number of people living at home were assessed by questionnaires. RESULTS: Among the 25 056 families from seven European countries cats (14.9%) were more common than dogs (12.0%). Allergic family history significantly reduced the odds to own a cat (adjusted combined random-effect OR 0.91; 95% CI 0.85-0.99), or dog (0.90; 0.86-0.94). A higher parental educational level had even more pronounced effects on cat (0.84; 0.71-0.98), and dog ownership (0.61; 0.54-0.70). Elder siblings reduced the odds to own cats, but not dogs. Convenient ground access significantly increased the odds, whereas crowding at home was not associated with cat or dog ownership. CONCLUSIONS: The chances to own a cat or dog were significantly reduced in allergic families, in parents with a higher educational level, and in homes without convenient ground access. In addition to parental allergies, social and housing factors should be considered as potential confounders in studies on pet exposure and allergic diseases.

Differential effects of DRB1*0301 and DQA1*0501-DQB1*0201 on the activation and progression of islet cell autoimmunity.

Autoimmune diabetes shows extreme variation in age of onset and clinical presentation, although most studies have been done in children with the most severe subtype. Disease risk is strongly associated with HLA-DRB1*0301-DQA1*0501-DQB1*0201 (DR3-DQ2), but it has not been possible to separate the effects of the DR and DQ alleles. We have identified a large Bedouin kindred in which a high prevalence of islet autoimmunity is associated with two different DR3 haplotypes, one carrying the usual DQ2 and the other carrying DQA1*0102-DQB1*0502 (DQ5). Results of prospective follow-up studies indicate that DR3 is associated with the initial activation of islet autoimmunity whereas DQ2 is associated with early-onset and severe clinical disease. The association signals map to a 350-kb interval, thus implicating primary effects for DR3 and DQ2. Overall, our results emphasize the importance of prospective genetic studies that examine the full range of variation in the initiation, progression and expression of autoimmune disease.

Meal size and feeding frequency influence serum leptin concentration in yearling horses.

Energy is an essential nutrient for all horses, and it is especially important in performance horses, pregnant and lactating mares, and young growing horses. A negative energy balance in horses such as these may result in unsatisfactory performance, decreased fertility, or slow growth. Therefore, ensuring adequate energy intake is an important aspect of the nutritional management of the equine. This study was undertaken to investigate the effects of feeding large, carbohydrate-rich, concentrate meals on the satiety-inducing hormone, leptin. Three groups of yearling horses were rotated through 3 feeding schedules in a replicated 3x3 Latin square design. Horses were fed 2, 3, or 4 times per day (2x, 3x, and 4xfeeding schedules, respectively), each for a period of 11 d, with the total amount of daily feed held constant. Horses were weighed and BCS was determined on the first day of each period. Blood samples were collected before the morning meal on d 1, 4, and 7 of each period. Additionally, blood was sampled for the last 24 h of the 2xand 4xdietary periods. Neither weight nor BCS changed during the study (P = 0.99 and P = 0.28, respectively). Both mean and peak plasma glucose were greatest in 2xhorses (P < 0.05), as were mean areas under the curve. Serum leptin concentration increased in 2xhorses (P < 0.05), but not in horses fed 3 or 4 times daily. Leptin was elevated in horses with greater BCS (P < 0.05) and increased steadily throughout the study (P < 0.05). Data from the 24-h collection indicated that 2xhorses had fluctuations in leptin production throughout the day (P < 0.05), whereas horses fed 4 times daily did not. Overall, this study indicates that feeding horses 2 large concentrate meals daily can increase mean serum leptin concentrations and may cause fluctuations in leptin production over a 24-h period. This departure from baseline leptin concentration has the potential to affect appetite, along with numerous other physiological processes.

European birth cohort studies on asthma and atopic diseases: II. Comparison of outcomes and exposures--a GA2LEN initiative.

BACKGROUND: The Global Allergy and Asthma European Network (GA2LEN) is a consortium of 26 leading European research centres committed to establish a European research area of excellence in the field of allergy and asthma. AIM: One of the GA2LEN work packages was designed to identify and compare the existing European birth cohort studies on asthma and atopic diseases. The present review compares their subjective and objective outcomes as well as exposure variables. METHODS: A common database was established to assess study characteristics of observational birth cohort studies designed to examine asthma and atopic diseases. Data were collected by visiting most of the participating research teams and interviewing all relevant study personnel. For each study, the type of objective/subjective outcome parameters and potentially influential factors were recorded precisely for every time point during follow-up. RESULTS: Eighteen birth cohort studies on asthma and atopic diseases were identified in eight European countries. Thirteen studies collected data on specific immunoglobulin E (IgE) to various inhalant and food allergens, whereas 12 performed skin prick tests (many at several time points during follow up). Several studies measured lung function, but across the cohorts no comparable standard procedures were used. For subjective evaluation of asthma and allergic rhinitis most studies applied the ISAAC questionnaire (sometimes modified), whereas the assessment of eczema was rather heterogeneous across the studies. CONCLUSION: This GA2LEN initiative established a unique common database of 18 European birth cohorts on asthma and atopic diseases. For selected cohorts, it seems that pooling data and performing common analyses may be possible to examine associations between certain exposure variables (e.g. pet ownership, tobacco smoke exposure and day-care) and selected outcome measures for atopy, asthma or allergic rhinitis (e.g. sensitization assessed by IgE or skin prick tests, doctor's diagnosis of asthma, parental perception regarding asthma/wheezing or hay fever symptoms).

European birth cohort studies on asthma and atopic diseases: I. Comparison of study designs -- a GALEN initiative.

BACKGROUND: The reasons for the rise in asthma and allergies remain unclear. To identify risk or protective factors, it is essential to carry out longitudinal epidemiological studies, preferably birth cohort studies. In Europe, several birth cohort studies on asthma and atopic diseases have been initiated over the last two decades. AIM: One of the work packages within the Global Allergy and Asthma European Network (GA(2)LEN) project was designed to identify and compare European birth cohorts on asthma and atopic diseases. The present review (part I) describes their objectives, study settings, recruitment process and follow-up rates. A subsequent review (part II) will compare outcome and exposure parameters. METHODS: For each birth cohort, we collected detailed information regarding recruitment process, study setting, baseline data (pregnancy, birth, parents/siblings) as well as follow-up rates, outcome and exposure parameters at each time point. RESULTS: We identified and assessed 18 European birth cohorts on asthma, allergic rhinitis and eczema. Six of these studies also focused on food allergies. The birth cohorts were mostly initiated in the 1990s with predominantly urban/metropolitan settings. Many studies were able to maintain high follow-up rates, even after five or more years. CONCLUSIONS: Due to the unique cooperation within the GA(2)LEN project a common database was established containing study characteristics of European birth cohorts on asthma and atopic diseases. This can be used as a basis for evaluating the possibility to pool data and perform meta-analyses, as well as to recommend criteria for conducting future birth cohorts.

Estimating relative population sizes from simulated data sets and the question of greater African effective size.

Previous genetic and craniometric studies have suggested greater genetic diversity and a larger effective size in Africa. Several demographic scenarios can explain a larger African effective size, and anthropological geneticists have attempted to obtain better estimates of relative population sizes among continental regions in the Old World. A least-squares approach of estimating relative population weights was developed by Relethford and Harpending ([1994] Am. J. Phys. Anthropol. 95:249-270), who applied it to craniometric and genetic data sets and concluded that the ratio of African, Asian, and European effective sizes was 3:1:1, respectively; another data set of short tandem repeat (STR) markers yielded a similar estimate of 7:1:2. However, an estimate from restriction site polymorphism (RSP, also known as restriction fragment length polymorphism, or RFLP) data yielded a very different estimate of 1:1:8. Thus, the European and not the African effective size was largest. Simulations showed that this was the result of ascertainment bias in which polymorphic markers were originally identified in a small panel of Caucasians, leading to inflated heterozygosity in the European sample and thus an inflated population weight. This paper extends those computer simulations to incorporate not only ascertainment bias but also interpopulation gene flow and demographic expansion in two types of genetic data, single nucleotide polymorphisms (SNPs, which are similar but not precisely identical to RSPs) and STRs. The effects of these three parameters on SNP and STR relative weight estimates are described. Simulations show that the ascertainment scheme affects SNP data but not STR data. Gene flow has a noticeable effect on the bias and efficiency of the estimates in both types of genetic data. Population expansions have a large effect only in one ascertainment scheme in the simulated SNP data and no effect in STR data. Relative population weight estimates from four published STR data sets are also reported. These estimates are similar to each other: all show a larger African weight and a European weight somewhat larger than the Asian weight. Because the STR simulations show that when gene flow is greater than 0.01 migrants per generation the African population weight is biased upward, it is likely that the African weights in the four STR data sets are inflated. However, the simulations suggest that the African effective size is still largest of the three regions and is probably at least as great as the sum of the Asian and European effective sizes.

Effects of ascertainment bias on recovering human demographic history.

In recent years multilocus data sets have been used to study the demographic history of human populations. In this paper (1) analyses previously done on 60 short tandem repeat (STR) loci are repeated on 30 restriction site polymorphism (RSP) markers; (2) relative population weights are estimated from the RSP data set and compared to previously published estimates from STR and craniometric data sets; and (3) computer simulations are performed to show the effects of ascertainment bias on relative population weight estimates. Not surprisingly, given that the RSP markers were originally identified in a small panel of Caucasians, estimates of relative population weights are biased and the European population weight is artificially inflated. However, the effects of ascertainment bias are not apparent in a principal components plot or estimates of FST. Ascertainment bias can have a large effect in other genetic systems with inherently low heterozygosity such as Alus or single nucleotide polymorphisms (SNPs), and care must be taken to have prior knowledge of how polymorphic markers in a given data set were originally identified. Otherwise, results can be skewed and interpretations faulty.